150-543: See text . Ectoprocta (Nitsche, 1869) (formerly subphylum of Bryozoa) Bryozoa (also known as the Polyzoa , Ectoprocta or commonly as moss animals ) are a phylum of simple, aquatic invertebrate animals, nearly all living in sedentary colonies . Typically about 0.5 millimetres ( 1 ⁄ 64 in) long, they have a special feeding structure called a lophophore , a "crown" of tentacles used for filter feeding . Most marine bryozoans live in tropical waters, but
300-614: A coelom , an internal cavity lined by mesothelium . Some encrusting bryozoan colonies with mineralized exoskeletons look very like small corals. However, bryozoan colonies are founded by an ancestrula, which is round rather than shaped like a normal zooid of that species. On the other hand, the founding polyp of a coral has a shape like that of its daughter polyps, and coral zooids have no coelom or lophophore . Entoprocts , another phylum of filter-feeders, look rather like bryozoans but their lophophore -like feeding structure has solid tentacles, their anus lies inside rather than outside
450-491: A coelom , while entoprocts have solid tentacles and no coelom. Hence the two groups are now widely regarded as separate phyla, and the name "Bryozoa" is now synonymous with "Ectoprocta". This has remained the majority view ever since, although most publications have preferred the name "Bryozoa" rather than "Ectoprocta". Nevertheless, some notable scientists have continued to regard the "Ectoprocta" and Entoprocta as close relatives and group them under "Bryozoa". The ambiguity about
600-746: A dasyclad alga. Early fossils are mainly of erect forms, but encrusting forms gradually became dominant. It is uncertain whether the phylum is monophyletic . Bryozoans' evolutionary relationships to other phyla are also unclear, partly because scientists' view of the family tree of animals is mainly influenced by better-known phyla. Both morphological and molecular phylogeny analyses disagree over bryozoans' relationships with entoprocts, about whether bryozoans should be grouped with brachiopods and phoronids in Lophophorata , and whether bryozoans should be considered protostomes or deuterostomes . Bryozoans, phoronids and brachiopods strain food out of
750-409: A "cystid", which provides the body wall and produces the exoskeleton , and a " polypide ", which holds the organs. Zooids have no special excretory organs, and autozooids' polypides are scrapped when they become overloaded with waste products; usually the body wall then grows a replacement polypide. Their gut is U-shaped, with the mouth inside the crown of tentacles and the anus outside it. Zooids of all
900-436: A bryozoan. The analysis also concluded that the classes Phylactolaemata, Stenolaemata and Gymnolaemata are also monophyletic, but could not determine whether Stenolaemata are more closely related to Phylactolaemata or Gymnolaemata . The Gymnolaemata are traditionally divided into the soft-bodied Ctenostomatida and mineralized Cheilostomata, but the 2009 analysis considered it more likely that neither of these orders
1050-458: A certain degree of evolutionary relatedness (the phylogenetic definition). Attempting to define a level of the Linnean hierarchy without referring to (evolutionary) relatedness is unsatisfactory, but a phenetic definition is useful when addressing questions of a morphological nature—such as how successful different body plans were. The most important objective measure in the above definitions
1200-407: A character unique to a sub-set of the crown group. Furthermore, organisms in the stem group of a phylum can possess the "body plan" of the phylum without all the characteristics necessary to fall within it. This weakens the idea that each of the phyla represents a distinct body plan. A classification using this definition may be strongly affected by the chance survival of rare groups, which can make
1350-499: A colony because there are so few gonozooids in one colony. The aperture in gonozooids, which is called an ooeciopore, acts as a point for larvae to exit. Some gonozooids have very complex shapes with autozooidal tubes passing through chambers within them. All larvae released from a gonozooid are clones created by division of a single egg; this is called monozygotic polyembryony , and is a reproductive strategy also used by armadillos . Cheilostome bryozoans also brood their embryos; one of
1500-431: A colony's lineage to survive even if severe conditions kill the mother colony. Predators of marine bryozoans include sea slugs (nudibranchs), fish, sea urchins , pycnogonids , crustaceans , mites and starfish . Freshwater bryozoans are preyed on by snails, insects, and fish. In Thailand , many populations of one freshwater species have been wiped out by an introduced species of snail. Membranipora membranacea ,
1650-518: A fast-growing invasive bryozoan off the northeast and northwest coasts of the US, has reduced kelp forests so much that it has affected local fish and invertebrate populations. Bryozoans have spread diseases to fish farms and fishermen. Chemicals extracted from a marine bryozoan species have been investigated for treatment of cancer and Alzheimer's disease , but analyses have not been encouraging. Mineralized skeletons of bryozoans first appear in rocks from
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#17327809642881800-648: A few are found in oceanic trenches and polar waters. The bryozoans are classified as the marine bryozoans (Stenolaemata), freshwater bryozoans (Phylactolaemata), and mostly-marine bryozoans (Gymnolaemata), a few members of which prefer brackish water . 5,869 living species are known. Originally all of the crown group Bryozoa were colonial, but as an adaptation to a mesopsammal (interstitial spaces in marine sand) life or to deep-sea habitats, secondarily solitary forms have since evolved. Solitary species has been described in four genera ; Aethozooides , Aethozoon , Franzenella and Monobryozoon ). The latter having
1950-402: A flexible membrane that replaces part of the exoskeleton, and transverse muscles anchored on the far side of the exoskeleton increase the fluid pressure by pulling the membrane inwards. In others there is no gap in the protective skeleton, and the transverse muscles pull on a flexible sac which is connected to the water outside by a small pore; the expansion of the sac increases the pressure inside
2100-401: A flexible tube called the "invert", which can be turned inside-out and withdrawn into the polypide, rather like the finger of a rubber glove; in this position the lophophore lies inside the invert and is folded like the spokes of an umbrella. The invert is withdrawn, sometimes within 60 milliseconds , by a pair of retractor muscles that are anchored at the far end of the cystid. Sensors at
2250-447: A free-swimming blastula embryo in as few as 12 hours. Initially a simple ball of cells, the blastula soon transforms into a cone-shaped echinopluteus larva. In most species, this larva has 12 elongated arms lined with bands of cilia that capture food particles and transport them to the mouth. In a few species, the blastula contains supplies of nutrient yolk and lacks arms, since it has no need to feed. Several months are needed for
2400-602: A group containing Viridiplantae and the algal Rhodophyta and Glaucophyta divisions. The definition and classification of plants at the division level also varies from source to source, and has changed progressively in recent years. Thus some sources place horsetails in division Arthrophyta and ferns in division Monilophyta, while others place them both in Monilophyta, as shown below. The division Pinophyta may be used for all gymnosperms (i.e. including cycads, ginkgos and gnetophytes), or for conifers alone as below. Since
2550-504: A hemal system with a complex network of vessels in the mesenteries around the gut, but little is known of the functioning of this system. However, the main circulatory fluid fills the general body cavity, or coelom . This coelomic fluid contains phagocytic coelomocytes, which move through the vascular and hemal systems and are involved in internal transport and gas exchange. The coelomocytes are an essential part of blood clotting , but also collect waste products and actively remove them from
2700-459: A major source of the carbonate minerals that make up limestones, and their fossils are incredibly common in marine sediments worldwide from the Ordovician onward. However, unlike corals and other colonial animals found in the fossil record, Bryozoan colonies did not reach large sizes. Fossil bryozoan colonies are typically found highly fragmented and scattered; the preservation of complete zoaria
2850-416: A mistranslation. Aristotle's lantern is actually referring to the whole shape of sea urchins, which look like the ancient lamps of Aristotle's time. Heart urchins are unusual in not having a lantern. Instead, the mouth is surrounded by cilia that pull strings of mucus containing food particles towards a series of grooves around the mouth. The lantern, where present, surrounds both the mouth cavity and
3000-434: A multipart process which dramatically rearranges its structure by invagination to produce the three germ layers , involving an epithelial-mesenchymal transition ; primary mesenchyme cells move into the blastocoel and become mesoderm . It has been suggested that epithelial polarity together with planar cell polarity might be sufficient to drive gastrulation in sea urchins. An unusual feature of sea urchin development
3150-456: A new dent becomes the point from which the gut grows. The ectoproct coelom is formed by neither of the processes used by other bilaterians, enterocoely , in which pouches that form on the wall of the gut become separate cavities, nor schizocoely , in which the tissue between the gut and the body wall splits, forming paired cavities. When entoprocts were discovered in the 19th century, they and bryozoans (ectoprocts) were regarded as classes within
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#17327809642883300-400: A phylum based on body plan has been proposed by paleontologists Graham Budd and Sören Jensen (as Haeckel had done a century earlier). The definition was posited because extinct organisms are hardest to classify: they can be offshoots that diverged from a phylum's line before the characters that define the modern phylum were all acquired. By Budd and Jensen's definition, a phylum is defined by
3450-471: A phylum much more diverse than it would be otherwise. Total numbers are estimates; figures from different authors vary wildly, not least because some are based on described species, some on extrapolations to numbers of undescribed species. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of the total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million. The kingdom Plantae
3600-706: A phylum, other phylum-level ranks appear, such as the case of Bacillariophyta (diatoms) within Ochrophyta . These differences became irrelevant after the adoption of a cladistic approach by the ISP, where taxonomic ranks are excluded from the classifications after being considered superfluous and unstable. Many authors prefer this usage, which lead to the Chromista-Protozoa scheme becoming obsolete. Currently there are 40 bacterial phyla (not including " Cyanobacteria ") that have been validly published according to
3750-401: A set of characters shared by all its living representatives. This approach brings some small problems—for instance, ancestral characters common to most members of a phylum may have been lost by some members. Also, this definition is based on an arbitrary point of time: the present. However, as it is character based, it is easy to apply to the fossil record. A greater problem is that it relies on
3900-559: A species that is symbiotic with hermit crabs and lives on their shells. These zooids are smaller than the others and have four short tentacles and four long tentacles, unlike the autozooids which have 15–16 tentacles. Androzooids are also found in species with mobile colonies that can crawl around. It is possible that androzooids are used to exchange sperm between colonies when two mobile colonies or bryozoan-encrusted hermit crabs happen to encounter one another. Spinozooids are hollow, movable spines, like very slender, small tubes, present on
4050-461: A statocyst-like organ with a supposed excretory function. The terms Polyzoa and Bryozoa were introduced in 1830 and 1831, respectively. Soon after it was named, another group of animals was discovered whose filtering mechanism looked similar, so it was included in Bryozoa until 1869, when the two groups were noted to be very different internally. The new group was given the name " Entoprocta ", while
4200-437: A strength that allow them to overcome the excellent protective features of sea urchins. Left unchecked by predators, urchins devastate their environments, creating what biologists call an urchin barren , devoid of macroalgae and associated fauna . Sea urchins graze on the lower stems of kelp, causing the kelp to drift away and die. Loss of the habitat and nutrients provided by kelp forests leads to profound cascade effects on
4350-401: A subjective decision about which groups of organisms should be considered as phyla. The approach is useful because it makes it easy to classify extinct organisms as " stem groups " to the phyla with which they bear the most resemblance, based only on the taxonomically important similarities. However, proving that a fossil belongs to the crown group of a phylum is difficult, as it must display
4500-411: A toothband with a hard tooth pointing towards the centre of the mouth. Specialised muscles control the protrusion of the apparatus and the action of the teeth, and the animal can grasp, scrape, pull and tear. The structure of the mouth and teeth have been found to be so efficient at grasping and grinding that similar structures have been tested for use in real-world applications. On the upper surface of
4650-456: A type of avicularia, the operculum is modified to form a long bristle that has a wide range of motion. They may function as defenses against predators and invaders, or as cleaners. In some species that form mobile colonies, vibracula around the edges are used as legs for burrowing and walking. Kenozooids (from the Greek kenós 'empty') consist only of the body wall and funicular strands crossing
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4800-435: A variety of functions other than feeding; colony members are genetically identical and co-operate, rather like the organs of larger animals. What type of zooid grows where in a colony is determined by chemical signals from the colony as a whole or sometimes in response to the scent of predators or rival colonies. The bodies of all types have two main parts. The cystid consists of the body wall and whatever type of exoskeleton
4950-406: A way similar to that of starfish; regular sea urchins do not have any favourite walking direction. The tube feet protrude through pairs of pores in the test, and are operated by a water vascular system ; this works through hydraulic pressure , allowing the sea urchin to pump water into and out of the tube feet. During locomotion, the tube feet are assisted by the spines which can be used for pushing
5100-548: A wide range of invertebrates, such as mussels , polychaetes , sponges , brittle stars, and crinoids, making them omnivores, consumers at a range of trophic levels . Mass mortality of sea urchins was first reported in the 1970s, but diseases in sea urchins had been little studied before the advent of aquaculture. In 1981, bacterial "spotting disease" caused almost complete mortality in juvenile Pseudocentrotus depressus and Hemicentrotus pulcherrimus , both cultivated in Japan;
5250-415: Is secreted by the epidermis . The exoskeleton may be organic ( chitin , polysaccharide or protein ) or made of the mineral calcium carbonate . The latter is always absent in freshwater species. The body wall consists of the epidermis, basal lamina (a mat of non-cellular material), connective tissue , muscles, and the mesothelium which lines the coelom (main body cavity) – except that in one class,
5400-474: Is a paraphyletic taxon, which is less acceptable to present-day biologists than in the past. Proposals have been made to divide it among several new kingdoms, such as Protozoa and Chromista in the Cavalier-Smith system . Protist taxonomy has long been unstable, with different approaches and definitions resulting in many competing classification schemes. Many of the phyla listed below are used by
5550-442: Is a large nerve ring encircling the mouth just inside the lantern. From the nerve ring, five nerves radiate underneath the radial canals of the water vascular system, and branch into numerous finer nerves to innervate the tube feet, spines, and pedicellariae . Sea urchins are sensitive to touch, light, and chemicals. There are numerous sensitive cells in the epithelium, especially in the spines, pedicellaria and tube feet, and around
5700-504: Is already exhausted. They are formed by patches of non-feeding heterozooids. New chimneys appear near the edges of expanding colonies, at points where the speed of the outflow is already high, and do not change position if the water flow changes. Some freshwater species secrete a mass of gelatinous material, up to 1 m (3 ft 3 in) in diameter, to which the zooids stick. Other freshwater species have plant-like shapes with "trunks" and "branches", which may stand erect or spread over
5850-516: Is complex and not completely consistent. Works since 2000 have used various names to resolve the ambiguity, including: "Bryozoa", "Ectoprocta", "Bryozoa (Ectoprocta)", and "Ectoprocta (Bryozoa)". Some have used more than one approach in the same work. The common name "moss animals" is the literal meaning of "Bryozoa", from Greek βρυόν ('moss') and ζῷα ('animals'), based on the mossy appearance of encrusting species. Until 2008 there were "inadequately known and misunderstood type species belonging to
6000-405: Is defined in various ways by different biologists (see Current definitions of Plantae ). All definitions include the living embryophytes (land plants), to which may be added the two green algae divisions, Chlorophyta and Charophyta , to form the clade Viridiplantae . The table below follows the influential (though contentious) Cavalier-Smith system in equating "Plantae" with Archaeplastida ,
6150-458: Is derived from the Old French herichun , from Latin ericius ('hedgehog'). Like other echinoderms, sea urchin early larvae have bilateral symmetry, but they develop five-fold symmetry as they mature. This is most apparent in the "regular" sea urchins, which have roughly spherical bodies with five equally sized parts radiating out from their central axes. The mouth is at the base of
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6300-409: Is established before the egg is fertilized. The oral-aboral axis is specified early in cleavage, and the left-right axis appears at the late gastrula stage. In most cases, the female's eggs float freely in the sea, but some species hold onto them with their spines, affording them a greater degree of protection. The unfertilized egg meets with the free-floating sperm released by males, and develops into
6450-399: Is feasible because the loss of zooids to a single attack is unlikely to be significant. Colonies of some encrusting species also produce special heterozooids to limit the expansion of other encrusting organisms, especially other bryozoans. In some cases this response is more belligerent if the opposition is smaller, which suggests that zooids on the edge of a colony can somehow sense the size of
6600-481: Is generally included in kingdom Fungi, though its exact relations remain uncertain, and it is considered a protozoan by the International Society of Protistologists (see Protista , below). Molecular analysis of Zygomycota has found it to be polyphyletic (its members do not share an immediate ancestor), which is considered undesirable by many biologists. Accordingly, there is a proposal to abolish
6750-409: Is known as Aristotle's lantern from Aristotle 's description in his History of Animals (translated by D'Arcy Thompson ): ... the urchin has what we mainly call its head and mouth down below, and a place for the issue of the residuum up above. The urchin has, also, five hollow teeth inside, and in the middle of these teeth a fleshy substance serving the office of a tongue . Next to this comes
6900-629: Is monophyletic and that mineralized skeletons probably evolved more than once within the early Gymnolaemata. Bryozoans' relationships with other phyla are uncertain and controversial. Traditional phylogeny, based on anatomy and on the development of the adult forms from embryos , has produced no enduring consensus about the position of ectoprocts. Attempts to reconstruct the family tree of animals have largely ignored ectoprocts and other "minor phyla", which have received little scientific study because they are generally tiny, have relatively simple body plans, and have little impact on human economies – despite
7050-499: Is not obvious in the living animal, but is easily visible in the dried test . Specifically, the term "sea urchin" refers to the "regular echinoids", which are symmetrical and globular, and includes several different taxonomic groups, with two subclasses: Euechinoidea ("modern" sea urchins, including irregular ones) and Cidaroidea , or "slate-pencil urchins", which have very thick, blunt spines, with algae and sponges growing on them. The "irregular" sea urchins are an infra-class inside
7200-428: Is present. Densities decrease in winter when storms cause them to seek protection in cracks and around larger underwater structures. The shingle urchin ( Colobocentrotus atratus ), which lives on exposed shorelines, is particularly resistant to wave action. It is one of the few sea urchin that can survive many hours out of water. Sea urchins can be found in all climates, from warm seas to polar oceans. The larvae of
7350-436: Is the "certain degree" that defines how different organisms need to be members of different phyla. The minimal requirement is that all organisms in a phylum should be clearly more closely related to one another than to any other group. Even this is problematic because the requirement depends on knowledge of organisms' relationships: as more data become available, particularly from molecular studies, we are better able to determine
7500-454: Is the aggregate of all species which have gradually evolved from one and the same common original form, as, for example, all vertebrates. We name this aggregate [a] Stamm [i.e., stock] ( Phylon )." In plant taxonomy , August W. Eichler (1883) classified plants into five groups named divisions, a term that remains in use today for groups of plants, algae and fungi. The definitions of zoological phyla have changed from their origins in
7650-400: Is the replacement of the larva's bilateral symmetry by the adult's broadly fivefold symmetry. During cleavage, mesoderm and small micromeres are specified. At the end of gastrulation, cells of these two types form coelomic pouches. In the larval stages, the adult rudiment grows from the left coelomic pouch; after metamorphosis, that rudiment grows to become the adult. The animal-vegetal axis
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#17327809642887800-571: Is uncommon in the fossil record, and relatively little study has been devoted to reassembling fragmented zoaria. The largest known fossil colonies are branching trepostome bryozoans from Ordovician rocks in the United States, reaching 66 centimeters in height. The oldest species with a mineralized skeleton occurs in the Lower Ordovician . It is likely that the first bryozoans appeared much earlier and were entirely soft-bodied, and
7950-655: The Bacteriological Code Currently there are 2 phyla that have been validly published according to the Bacteriological Code Other phyla that have been proposed, but not validly named, include: Sea urchin Sea urchins or urchins ( / ˈ ɜːr tʃ ɪ n z / ) are typically spiny , globular animals , echinoderms in the class Echinoidea. About 950 species live on the seabed, inhabiting all oceans and depth zones from
8100-580: The Bilateria , along with chordates , arthropods , annelids and molluscs . Sea urchins are found in every ocean and in every climate, from the tropics to the polar regions , and inhabit marine benthic (sea bed) habitats, from rocky shores to hadal zone depths. The fossil record of the Echinoids dates from the Ordovician period, some 450 million years ago. The closest echinoderm relatives of
8250-565: The Catalogue of Life , and correspond to the Protozoa-Chromista scheme, with updates from the latest (2022) publication by Cavalier-Smith . Other phyla are used commonly by other authors, and are adapted from the system used by the International Society of Protistologists (ISP). Some of the descriptions are based on the 2019 revision of eukaryotes by the ISP. The number of protist phyla varies greatly from one classification to
8400-519: The International Code of Nomenclature for algae, fungi, and plants accepts the terms as equivalent. Depending on definitions, the animal kingdom Animalia contains about 31 phyla, the plant kingdom Plantae contains about 14 phyla, and the fungus kingdom Fungi contains about 8 phyla. Current research in phylogenetics is uncovering the relationships among phyla within larger clades like Ecdysozoa and Embryophyta . The term phylum
8550-550: The Mesozoic are fairly equally divided by erect and encrusting forms, and more recent ones are predominantly encrusting. Fossils of the soft, freshwater phylactolaemates are very rare, appear in and after the Late Permian (which began about 260 million years ago ) and consist entirely of their durable statoblasts. There are no known fossils of freshwater members of other classes. Scientists are divided about whether
8700-482: The Middle Ordovician period ( circa 465 Mya ). There is a rich fossil record, their hard tests made of calcite plates surviving in rocks from every period since then. Spines are present in some well-preserved specimens, but usually only the test remains. Isolated spines are common as fossils. Some Jurassic and Cretaceous Cidaroida had very heavy, club-shaped spines. Most fossil echinoids from
8850-538: The Paleozoic era are incomplete, consisting of isolated spines and small clusters of scattered plates from crushed individuals, mostly in Devonian and Carboniferous rocks. The shallow-water limestones from the Ordovician and Silurian periods of Estonia are famous for echinoids. Paleozoic echinoids probably inhabited relatively quiet waters. Because of their thin tests, they would certainly not have survived in
9000-504: The anus , which is located on the invert, outside and usually below the lophophore. A network of strands of mesothelium called "funiculi" ("little ropes") connects the mesothelium covering the gut with that lining the body wall. The wall of each strand is made of mesothelium, and surrounds a space filled with fluid, thought to be blood. A colony's zooids are connected, enabling autozooids to share food with each other and with any non-feeding heterozooids. The method of connection varies between
9150-409: The appendages of others. In some species the snapping zooids are mounted on a peduncle (stalk), their bird-like appearance responsible for the term – Charles Darwin described these as like "the head and beak of a vulture in miniature, seated on a neck and capable of movement". Stalked avicularia are placed upside-down on their stalks. The "lower jaws" are modified versions of the opercula that protect
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#17327809642889300-429: The esophagus , and then the stomach , divided into five parts, and filled with excretion, all the five parts uniting at the anal vent, where the shell is perforated for an outlet ... In reality the mouth-apparatus of the urchin is continuous from one end to the other, but to outward appearance it is not so, but looks like a horn lantern with the panes of horn left out. However, this has recently been proven to be
9450-412: The genus Thalamoporella , structures that resemble an open head of lettuce. The most common marine form, however, is encrusting, in which a one-layer sheet of zooids spreads over a hard surface or over seaweed. Some encrusting colonies may grow to over 50 cm (1 ft 8 in) and contain about 2,000,000 zooids. These species generally have exoskeletons reinforced with calcium carbonate , and
9600-700: The hadal zone and have been collected as deep as 6850 metres beneath the surface in the Sunda Trench . Nevertheless, this makes sea urchin the class of echinoderms living the least deep, compared to brittle stars , starfish and crinoids that remain abundant below 8,000 m (26,250 ft) and sea cucumbers which have been recorded from 10,687 m (35,100 ft). Population densities vary by habitat, with more dense populations in barren areas as compared to kelp stands. Even in these barren areas, greatest densities are found in shallow water. Populations are generally found in deeper water if wave action
9750-401: The larvae have large yolks , go to feed, and quickly settle on a surface. Others produce larvae that have little yolk but swim and feed for a few days before settling. After settling, all larvae undergo a radical metamorphosis that destroys and rebuilds almost all the internal tissues. Freshwater species also produce statoblasts that lie dormant until conditions are favorable, which enables
9900-402: The pharynx . At the top of the lantern, the pharynx opens into the esophagus, which runs back down the outside of the lantern, to join the small intestine and a single caecum . The small intestine runs in a full circle around the inside of the test, before joining the large intestine, which completes another circuit in the opposite direction. From the large intestine, a rectum ascends towards
10050-471: The slate pencil urchin are popular in aquaria, where they are useful for controlling algae. Fossil urchins have been used as protective amulets . Sea urchins are members of the phylum Echinodermata , which also includes starfish , sea cucumbers , sand dollars , brittle stars , and crinoids . Like other echinoderms, they have five-fold symmetry (called pentamerism ) and move by means of hundreds of tiny, transparent, adhesive " tube feet ". The symmetry
10200-418: The "crown" is a full circle. Among the freshwater bryozoans ( Phylactolaemata ) the crown appears U-shaped, but this impression is created by a deep dent in the rim of the crown, which has no gap in the fringe of tentacles. The sides of the tentacles bear fine hairs called cilia , whose beating drives a water current from the tips of the tentacles to their bases, where it exits. Food particles that collide with
10350-434: The Bryozoa (Ectoprocta) are a monophyletic group (whether they include all and only a single ancestor species and all its descendants), about what are the phylum's closest relatives in the family tree of animals, and even about whether they should be regarded as members of the protostomes or deuterostomes , the two major groups that account for all moderately complex animals. Molecular phylogeny, which attempts to work out
10500-537: The Cyclostome Bryozoan family Oncousoeciidae." Modern research and experiments have been done using low-vacuum scanning electron microscopy of uncoated type material to critically examine and perhaps revise the taxonomy of three genera belonging to this family, including Oncousoecia , Microeciella , and Eurystrotos . This method permits data to be obtained that would be difficult to recognize with an optical microscope. The valid type species of Oncousoecia
10650-588: The Early Ordovician period, making it the last major phylum to appear in the fossil record. This has led researchers to suspect that bryozoans arose earlier but were initially unmineralized, and may have differed significantly from fossilized and modern forms. In 2021, some research suggested Protomelission , a genus known from the Cambrian period , could be an example of an early bryozoan, but later research suggested that this taxon may instead represent
10800-516: The Entoprocta are not monophyletic, as the Phoronida are a sub-group of ectoprocts but the standard definition of Entoprocta excludes the Phoronida. In 2009 another molecular phylogeny study, using a combination of genes from mitochondria and the cell nucleus , concluded that Bryozoa is a monophyletic phylum, in other words includes all the descendants of a common ancestor that is itself
10950-649: The Euechinoidea, called Irregularia , and include Atelostomata and Neognathostomata . Irregular echinoids include flattened sand dollars , sea biscuits , and heart urchins . Together with sea cucumbers ( Holothuroidea ), they make up the subphylum Echinozoa , which is characterized by a globoid shape without arms or projecting rays. Sea cucumbers and the irregular echinoids have secondarily evolved diverse shapes. Although many sea cucumbers have branched tentacles surrounding their oral openings, these have originated from modified tube feet and are not homologous to
11100-660: The Ordovician fossils record the appearance of mineralized skeletons in this phylum. By the Arenigian stage of the Early Ordovician period , about 480 million years ago , all the modern orders of stenolaemates were present, and the ctenostome order of gymnolaemates had appeared by the Middle Ordovician, about 465 million years ago . The Early Ordovician fossils may also represent forms that had already become significantly different from
11250-656: The Ordovician period. Bryozoans take responsibility for many of the colony forms, which have evolved in different taxonomic groups and vary in sediment producing ability. The nine basic bryozoan colony-forms include: encrusting, dome-shaped, palmate, foliose, fenestrate, robust branching, delicate branching, articulated and free-living. Most of these sediments come from two distinct groups of colonies: domal, delicate branching, robust branching and palmate; and fenestrate. Fenestrate colonies generate rough particles both as sediment and components of stromatoporoids coral reefs. The delicate colonies however, create both coarse sediment and form
11400-497: The Zygomycota phylum. Its members would be divided between phylum Glomeromycota and four new subphyla incertae sedis (of uncertain placement): Entomophthoromycotina , Kickxellomycotina , Mucoromycotina , and Zoopagomycotina . Kingdom Protista (or Protoctista) is included in the traditional five- or six-kingdom model, where it can be defined as containing all eukaryotes that are not plants, animals, or fungi. Protista
11550-460: The ambulacral areas; their function is to help in gravitational orientation. Sea urchins are dioecious , having separate male and female sexes, although no distinguishing features are visible externally. In addition to their role in reproduction, the gonads are also nutrient storing organs, and are made up of two main type of cells: germ cells , and somatic cells called nutritive phagocytes. Regular sea urchins have five gonads, lying underneath
11700-454: The animal and the anus at the top; the lower surface is described as "oral" and the upper surface as "aboral". Several sea urchins, however, including the sand dollars, are oval in shape, with distinct front and rear ends, giving them a degree of bilateral symmetry. In these urchins, the upper surface of the body is slightly domed, but the underside is flat, while the sides are devoid of tube feet. This "irregular" body form has evolved to allow
11850-412: The animal is low in oxygen. Tube feet can also act as respiratory organs, and are the primary sites of gas exchange in heart urchins and sand dollars, both of which lack gills. The inside of each tube foot is divided by a septum which reduces diffusion between the incoming and outgoing streams of fluid. The nervous system of sea urchins has a relatively simple layout. With no true brain, the neural center
12000-415: The animals anchor themselves to sand or gravel and pull themselves through the sediments. Some authorities use the term avicularia (plural of avicularium ) to refer to any type of zooid in which the lophophore is replaced by an extension that serves some protective function, while others restrict the term to those that defend the colony by snapping at invaders and small predators, killing some and biting
12150-436: The animals to burrow through sand or other soft materials. The internal organs are enclosed in a hard shell or test composed of fused plates of calcium carbonate covered by a thin dermis and epidermis . The test is referred to as an endoskeleton rather than exoskeleton even though it encloses almost all of the urchin. This is because it is covered with a thin layer of muscle and skin; sea urchins also do not need to molt
12300-445: The anus is outside the feeding organ. A series of molecular phylogeny studies from 1996 to 2006 have also concluded that bryozoans (ectoprocts) and entoprocts are not sister groups. Phylum In biology , a phylum ( / ˈ f aɪ l əm / ; pl. : phyla ) is a level of classification or taxonomic rank below kingdom and above class . Traditionally, in botany the term division has been used instead of phylum, although
12450-451: The anus. Despite the names, the small and large intestines of sea urchins are in no way homologous to the similarly named structures in vertebrates. Digestion occurs in the intestine, with the caecum producing further digestive enzymes . An additional tube, called the siphon, runs beside much of the intestine, opening into it at both ends. It may be involved in resorption of water from food. The water vascular system leads downwards from
12600-497: The arms of the crinoids, sea stars, and brittle stars. Urchins typically range in size from 3 to 10 cm (1 to 4 in), but the largest species can reach up to 36 cm (14 in). They have a rigid, usually spherical body bearing moveable spines, which give the class the name Echinoidea (from the Greek ἐχῖνος ekhinos 'spine'). The name urchin is an old word for hedgehog , which sea urchins resemble; they have archaically been called sea hedgehogs . The name
12750-454: The base of the "crown" and they have no coelom . All bryozoans are colonial except for one genus , Monobryozoon . Individual members of a bryozoan colony are about 0.5 mm ( 1 ⁄ 64 in) long and are known as zooids , since they are not fully independent animals. All colonies contain feeding zooids, known as autozooids. Those of some groups also contain non-feeding heterozooids, also known as polymorphic zooids, which serve
12900-591: The body along or to lift the test off the substrate. Movement is generally related to feeding, with the red sea urchin ( Mesocentrotus franciscanus ) managing about 7.5 cm (3 in) a day when there is ample food, and up to 50 cm (20 in) a day where there is not. An inverted sea urchin can right itself by progressively attaching and detaching its tube feet and manipulating its spines to roll its body upright. Some species bury themselves in soft sediment using their spines, and Paracentrotus lividus uses its jaws to burrow into soft rocks. The mouth lies in
13050-400: The body and pushes the invert and lophophore out. In some species the retracted invert and lophophore are protected by an operculum ("lid"), which is closed by muscles and opened by fluid pressure. In one class , a hollow lobe called the "epistome" overhangs the mouth. The gut is U-shaped, running from the mouth, in the center of the lophophore, down into the animal's interior and then back to
13200-431: The body through the gills and tube feet. Most sea urchins possess five pairs of external gills attached to the peristomial membrane around their mouths. These thin-walled projections of the body cavity are the main organs of respiration in those urchins that possess them. Fluid can be pumped through the gills' interiors by muscles associated with the lantern, but this does not provide a continuous flow, and occurs only when
13350-423: The centre of the oral surface in regular urchins, or towards one end in irregular urchins. It is surrounded by lips of softer tissue, with numerous small, embedded bony pieces. This area, called the peristome, also includes five pairs of modified tube feet and, in many species, five pairs of gills. The jaw apparatus consists of five strong arrow-shaped plates known as pyramids, the ventral surface of each of which has
13500-633: The chalk of the Cretaceous period, serve as zone or index fossils. Because they are abundant and evolved rapidly, they enable geologists to date the surrounding rocks. In the Paleogene and Neogene periods ( circa 66 to 2.6 Mya), sand dollars (Clypeasteroida) arose. Their distinctive, flattened tests and tiny spines were adapted to life on or under loose sand in shallow water, and they are abundant as fossils in southern European limestones and sandstones. Echinoids are deuterostome animals, like
13650-427: The class Phylactolaemata is most closely related to Stenolaemata and Ctenostomatida , the classes that appear earliest in the fossil record. However, in 2005 a molecular phylogeny study that focused on phylactolaemates concluded that these are more closely related to the phylum Phoronida , and especially to the only phoronid species that is colonial, than they are to the other ectoproct classes. That implies that
13800-510: The colony through diverse channels. Some classes have specialist zooids like hatcheries for fertilized eggs, colonial defence structures, and root-like attachment structures. Cheilostomata is the most diverse order of bryozoan, possibly because its members have the widest range of specialist zooids. They have mineralized exoskeletons and form single-layered sheets which encrust over surfaces, and some colonies can creep very slowly by using spiny defensive zooids as legs. Each zooid consists of
13950-686: The colony. Because kenozooids' function is generally structural, they are called "structural polymorphs." Some heterozooids found in extinct trepostome bryozoans, called mesozooids, are thought to have functioned to space the feeding autozooids an appropriate distance apart. In thin sections of trepostome fossils, mesozooids can be seen in between the tubes that held autozooids; they are smaller tubes that are divided along their length by diaphragms, making them look like rows of box-like chambers sandwiched between autozooidal tubes. Gonozooids act as brood chambers for fertilized eggs. Almost all modern cyclostome bryozoans have them, but they can be hard to locate on
14100-401: The common methods is through ovicells, capsules attached to autozooids. The autozooids possessing ovicells are normally still able to feed, however, so these are not considered heterozooids. "Female" polymorphs are more common than "male" polymorphs, but specialized zooids that produce sperm are also known. These are called androzooids, and some are found in colonies of Odontoporella bishopi ,
14250-468: The cores of deep-water, subphotic biogenic mounds. Nearly all post- bryozoan sediments are made up of growth forms, with the addition to free-living colonies which include significant numbers of various colonies. "In contrast to the Palaeozoic, post-Palaeozoic bryozoans generated sediment varying more widely with the size of their grains; they grow as they moved from mud, to sand, to gravel." The phylum
14400-401: The different classes of bryozoans, ranging from quite large gaps in the body walls to small pores through which nutrients are passed by funiculi. There is a nerve ring round the pharynx (throat) and a ganglion that serves as a brain to one side of this. Nerves run from the ring and ganglion to the tentacles and to the rest of the body. Bryozoans have no specialized sense organs, but cilia on
14550-438: The disease recurred in succeeding years. It was divided into a cool-water "spring" disease and a hot-water "summer" form. Another condition, bald sea urchin disease , causes loss of spines and skin lesions and is believed to be bacterial in origin. Adult sea urchins are usually well protected against most predators by their strong and sharp spines, which can be venomous in some species. The small urchin clingfish lives among
14700-420: The evolutionary family tree of organisms by comparing their biochemistry and especially their genes , has done much to clarify the relationships between the better-known invertebrate phyla. However, the shortage of genetic data about "minor phyla" such as bryozoans and entoprocts has left their relationships to other groups unclear. The traditional view is that the Bryozoa are a monophyletic group, in which
14850-442: The fact that the "minor phyla" include most of the variety in the evolutionary history of animals. In the opinion of Ruth Dewel, Judith Winston, and Frank McKinney, "Our standard interpretation of bryozoan morphology and embryology is a construct resulting from over 100 years of attempts to synthesize a single framework for all invertebrates," and takes little account of some peculiar features of ectoprocts. In ectoprocts, all of
15000-446: The feeding apparatus or other specialized organs that take the place of the feeding apparatus. The most common type of zooid is the feeding autozooid, in which the polypide bears a "crown" of hollow tentacles called a lophophore , which captures food particles from the water. In all colonies a large percentage of zooids are autozooids, and some consist entirely of autozooids, some of which also engage in reproduction. The basic shape of
15150-507: The first publication of the APG system in 1998, which proposed a classification of angiosperms up to the level of orders , many sources have preferred to treat ranks higher than orders as informal clades. Where formal ranks have been provided, the traditional divisions listed below have been reduced to a very much lower level, e.g. subclasses . Wolf plants Hepatophyta Liver plants Coniferophyta Cone-bearing plant Phylum Microsporidia
15300-440: The fluid pressure by pulling on a flexible membrane. The actions of these snapping zooids are controlled by small, highly modified polypides that are located inside the "mouth" and bear tufts of short sensory cilia . These zooids appear in various positions: some take the place of autozooids, some fit into small gaps between autozooids, and small avicularia may occur on the surfaces of other zooids. In vibracula, regarded by some as
15450-415: The freshwater species are simultaneous hermaphrodites . Although those of many marine species function first as males and then as females, their colonies always contain a combination of zooids that are in their male and female stages. All species emit sperm into the water. Some also release ova into the water, while others capture sperm via their tentacles to fertilize their ova internally. In some species
15600-487: The greatest numbers of species, possibly because of their wide range of specialist zooids. Under the Linnaean system of classification , which is still used as a convenient way to label groups of organisms, living members of the phylum Bryozoa are divided into: Fossils of about 15,000 bryozoan species have been found. Bryozoans are among the three dominant groups of Paleozoic fossils. Bryozoans with calcitic skeletons were
15750-406: The interambulacral regions of the test, while the irregular forms mostly have four, with the hindmost gonad being absent; heart urchins have three or two. Each gonad has a single duct rising from the upper pole to open at a gonopore lying in one of the genital plates surrounding the anus. Some burrowing sand dollars have an elongated papilla that enables the liberation of gametes above the surface of
15900-401: The interior, and no polypide. The functions of these zooids include forming the stems of branching structures, acting as spacers that enable colonies to grow quickly in a new direction, strengthening the colony's branches, and elevating the colony slightly above its substrate for competitive advantages against other organisms. Some kenozooids are hypothesized to be capable of storing nutrients for
16050-574: The intertidal downwards, at an extremely wide range of depths. Some species, such as Cidaris abyssicola , can live at depths of several kilometres. Many genera are found in only the abyssal zone , including many cidaroids , most of the genera in the Echinothuriidae family, and the "cactus urchins" Dermechinus . One of the deepest-living families is the Pourtalesiidae , strange bottle-shaped irregular sea urchins that live in only
16200-626: The intertidal to 5,000 metres (16,000 ft; 2,700 fathoms). Their tests (hard shells) are round and spiny, typically from 3 to 10 cm (1 to 4 in) across. Sea urchins move slowly, crawling with their tube feet , and sometimes pushing themselves with their spines. They feed primarily on algae but also eat slow-moving or sessile animals. Their predators include sharks , sea otters , starfish , wolf eels , and triggerfish . Like all echinoderms, adult sea urchins have fivefold symmetry with their pluteus larvae featuring bilateral (mirror) symmetry ; The latter indicates that they belong to
16350-808: The larva to complete its development, the change into the adult form beginning with the formation of test plates in a juvenile rudiment which develops on the left side of the larva, its axis being perpendicular to that of the larva. Soon, the larva sinks to the bottom and metamorphoses into a juvenile urchin in as little as one hour. In some species, adults reach their maximum size in about five years. The purple urchin becomes sexually mature in two years and may live for twenty. Red sea urchins were originally thought to live 7 to 10 years but recent studies have shown that they can live for more than 100 years. Canadian red urchins have been found to be around 200 years old. Sea urchins feed mainly on algae , so they are primarily herbivores , but can feed on sea cucumbers and
16500-400: The larva's internal organs are destroyed during the metamorphosis to the adult form and the adult's organs are built from the larva's epidermis and mesoderm , while in other bilaterians some organs including the gut are built from endoderm . In most bilaterian embryos the blastopore, a dent in the outer wall, deepens to become the larva's gut, but in ectoprocts the blastopore disappears and
16650-435: The madreporite through the slender stone canal to the ring canal, which encircles the oesophagus. Radial canals lead from here through each ambulacral area to terminate in a small tentacle that passes through the ambulacral plate near the aboral pole. Lateral canals lead from these radial canals, ending in ampullae. From here, two tubes pass through a pair of pores on the plate to terminate in the tube feet. Sea urchins possess
16800-409: The marine ecosystem. Sea otters have re-entered British Columbia , dramatically improving coastal ecosystem health. The spines , long and sharp in some species, protect the urchin from predators . Some tropical sea urchins like Diadematidae , Echinothuriidae and Toxopneustidae have venomous spines. Other creatures also make use of these defences; crabs, shrimps and other organisms shelter among
16950-421: The mesothelium is split into two separate layers, the inner one forming a membranous sac that floats freely and contains the coelom, and the outer one attached to the body wall and enclosing the membranous sac in a pseudocoelom . The other main part of the bryozoan body, known as the polypide and situated almost entirely within the cystid, contains the nervous system, digestive system, some specialized muscles and
17100-507: The most abundant and diverse bryozoans from the Cretaceous to the present. Evidence compiled from the last 100 million years show that cheilostomatids consistently grew over cyclostomatids in territorial struggles, which may help to explain how cheilostomatids replaced cyclostomatids as the dominant marine bryozoans. Marine fossils from the Paleozoic era, which ended 251 million years ago , are mainly of erect forms, those from
17250-474: The mouth. Although they do not have eyes or eye spots (except for diadematids , which can follow a threat with their spines), the entire body of most regular sea urchins might function as a compound eye. In general, sea urchins are negatively attracted to light, and seek to hide themselves in crevices or under objects. Most species, apart from pencil urchins , have statocysts in globular organs called spheridia. These are stalked structures and are located within
17400-445: The name "Bryozoa" was promoted to phylum level to include the two classes Ectoprocta and Entoprocta. However, in 1869 Hinrich Nitsche regarded the two groups as quite distinct for a variety of reasons, and coined the name "Ectoprocta" for Ehrenberg's "Bryozoa". Despite their apparently similar methods of feeding, they differed markedly anatomically; in addition to the different positions of the anus, ectoprocts have hollow tentacles and
17550-411: The next. The Catalogue of Life includes Rhodophyta and Glaucophyta in kingdom Plantae, but other systems consider these phyla part of Protista. In addition, less popular classification schemes unite Ochrophyta and Pseudofungi under one phylum, Gyrista , and all alveolates except ciliates in one phylum Myzozoa , later lowered in rank and included in a paraphyletic phylum Miozoa . Even within
17700-464: The openings through which the lophophores protrude are on the top or outer surface. The moss-like appearance of encrusting colonies is responsible for the phylum's name ( Ancient Greek words βρύον brúon meaning 'moss' and ζῷον zôion meaning 'animal'). Large colonies of encrusting species often have " chimneys ", gaps in the canopy of lophophores, through which they swiftly expel water that has been sieved, and thus avoid re-filtering water that
17850-458: The opponent. Some species consistently prevail against certain others, but most turf wars are indecisive and the combatants soon turn to growing in uncontested areas. Bryozoans competing for territory do not use the sophisticated techniques employed by sponges or corals , possibly because the shortness of bryozoan lifespans makes heavy investment in turf wars unprofitable. Bryozoans have contributed to carbonate sedimentation in marine life since
18000-492: The original Bryozoa were called "Ectoprocta". Disagreements about terminology persisted well into the 20th century, but "Bryozoa" is now the generally accepted term. Colonies take a variety of forms, including fans, bushes and sheets. Single animals, called zooids , live throughout the colony and are not fully independent. These individuals can have unique and diverse functions. All colonies have "autozooids", which are responsible for feeding, excretion , and supplying nutrients to
18150-551: The original members of the phylum. Ctenostomes with phosphatized soft tissue are known from the Devonian. Other types of filter feeders appeared around the same time, which suggests that some change made the environment more favorable for this lifestyle. Fossils of cheilostomates , an order of gymnolaemates with mineralized skeletons, first appear in the Mid Jurassic , about 172 million years ago , and these have been
18300-539: The other hand, the highly parasitic phylum Mesozoa was divided into two phyla ( Orthonectida and Rhombozoa ) when it was discovered the Orthonectida are probably deuterostomes and the Rhombozoa protostomes . This changeability of phyla has led some biologists to call for the concept of a phylum to be abandoned in favour of placing taxa in clades without any formal ranking of group size. A definition of
18450-534: The past. A new genus has also been recently discovered called Junerossia in the family Stomachetosellidae, along with 10 relatively new species of bryozoa such as Alderina flaventa , Corbulella extenuata , Puellina septemcryptica , Junerossia copiosa , Calyptotheca kapaaensis , Bryopesanser serratus , Cribellopora souleorum , Metacleidochasma verrucosa , Disporella compta , and Favosipora adunca . Counts of formally described species range between 4,000 and 4,500. The Gymnolaemata and especially Cheilostomata have
18600-559: The pattern of budding by which they grow, the variety of zooids present and the type and amount of skeletal material they secrete . Some marine species are bush-like or fan-like, supported by "trunks" and "branches" formed by kenozooids, with feeding autozooids growing from these. Colonies of these types are generally unmineralized but may have exoskeletons made of chitin . Others look like small corals , producing heavy lime skeletons. Many species form colonies which consist of sheets of autozooids. These sheets may form leaves, tufts or, in
18750-481: The phylum Bryozoa, because both groups were sessile animals that filter-fed by means of a crown of tentacles that bore cilia . From 1869 onwards increasing awareness of differences, including the position of the entoproct anus inside the feeding structure and the difference in the early pattern of division of cells in their embryos , caused scientists to regard the two groups as separate phyla, and "Bryozoa" became just an alternative name for ectoprocts, in which
18900-456: The plates are covered in rounded tubercles to which the spines are attached. The spines are used for defence and for locomotion and come in a variety of forms. The inner surface of the test is lined by peritoneum . Sea urchins convert aqueous carbon dioxide using a catalytic process involving nickel into the calcium carbonate portion of the test. Most species have two series of spines, primary (long) and secondary (short), distributed over
19050-473: The polar sea urchin Sterechinus neumayeri have been found to use energy in metabolic processes twenty-five times more efficiently than do most other organisms. Despite their presence in nearly all the marine ecosystems, most species are found on temperate and tropical coasts, between the surface and some tens of meters deep, close to photosynthetic food sources. The earliest echinoid fossils date to
19200-475: The relationships between groups. So phyla can be merged or split if it becomes apparent that they are related to one another or not. For example, the bearded worms were described as a new phylum (the Pogonophora) in the middle of the 20th century, but molecular work almost half a century later found them to be a group of annelids , so the phyla were merged (the bearded worms are now an annelid family ). On
19350-444: The retracted lophophores in autozooids of some species, and are snapped shut "like a mousetrap" by similar muscles, while the beak-shaped upper jaw is the inverted body wall. In other species the avicularia are stationary box-like zooids laid the normal way up, so that the modified operculum snaps down against the body wall. In both types the modified operculum is opened by other muscles that attach to it, or by internal muscles that raise
19500-495: The scope of the name "Bryozoa" led to proposals in the 1960s and 1970s that it should be avoided and the unambiguous term "Ectoprocta" should be used. However, the change would have made it harder to find older works in which the phylum was called "Bryozoa", and the desire to avoid ambiguity, if applied consistently to all classifications, would have necessitated renaming of several other phyla and many lower-level groups. In practice, zoological naming of split or merged groups of animals
19650-489: The sea urchin are the sea cucumbers (Holothuroidea), which like them are deuterostomes , a clade that includes the chordates . ( Sand dollars are a separate order in the sea urchin class Echinoidea.) The animals have been studied since the 19th century as model organisms in developmental biology , as their embryos were easy to observe. That has continued with studies of their genomes because of their unusual fivefold symmetry and relationship to chordates. Species such as
19800-418: The sediment. The gonads are lined with muscles underneath the peritoneum, and these allow the animal to squeeze its gametes through the duct and into the surrounding sea water, where fertilization takes place. During early development, the sea urchin embryo undergoes 10 cycles of cell division , resulting in a single epithelial layer enveloping the blastocoel . The embryo then begins gastrulation ,
19950-399: The six Linnaean classes and the four embranchements of Georges Cuvier . Informally, phyla can be thought of as groupings of organisms based on general specialization of body plan . At its most basic, a phylum can be defined in two ways: as a group of organisms with a certain degree of morphological or developmental similarity (the phenetic definition), or a group of organisms with
20100-444: The spines of urchins such as Diadema ; juveniles feed on the pedicellariae and sphaeridia, adult males choose the tube feet and adult females move away to feed on shrimp eggs and molluscs. Sea urchins are one of the favourite foods of many lobsters , crabs , triggerfish , California sheephead , sea otter and wolf eels (which specialise in sea urchins). All these animals carry particular adaptations (teeth, pincers, claws) and
20250-473: The spines, and often adopt the colouring of their host. Some crabs in the Dorippidae family carry sea urchins, starfish, sharp shells or other protective objects in their claws. Pedicellariae are a good means of defense against ectoparasites, but not a panacea as some of them actually feed on it. The hemal system defends against endoparasites. Sea urchins are established in most seabed habitats from
20400-481: The surface of colonies, which probably are for defense. Some species have miniature nanozooids with small single-tentacled polypides, and these may grow on other zooids or within the body walls of autozooids that have degenerated. Although zooids are microscopic, colonies range in size from 1 cm ( 1 ⁄ 2 in) to over 1 m (3 ft 3 in). However, the majority are under 10 cm (4 in) across. The shapes of colonies vary widely, depend on
20550-541: The surface of the body, with the shortest at the poles and the longest at the equator. The spines are usually hollow and cylindrical. Contraction of the muscular sheath that covers the test causes the spines to lean in one direction or another, while an inner sheath of collagen fibres can reversibly change from soft to rigid which can lock the spine in one position. Located among the spines are several types of pedicellaria , moveable stalked structures with jaws. Sea urchins move by walking, using their many flexible tube feet in
20700-437: The surface. A few species can creep at about 2 cm ( 3 ⁄ 4 in) per day. Each colony grows by asexual budding from a single zooid known as the ancestrula, which is round rather than shaped like a normal zooid. This occurs at the tips of "trunks" or "branches" in forms that have this structure. Encrusting colonies grow round their edges. In species with calcareous exoskeletons, these do not mineralize until
20850-485: The tentacles act as sensors. Members of the genus Bugula grow towards the sun , and therefore must be able to detect light. In colonies of some species, signals are transmitted between zooids through nerves that pass through pores in the body walls, and coordinate activities such as feeding and the retraction of lophophores. The solitary individuals of Monobryozoon are autozooids with pear-shaped bodies. The wider ends have up to 15 short, muscular projections by which
21000-435: The tentacles are trapped by mucus , and further cilia on the inner surfaces of the tentacles move the particles towards the mouth in the center. The method used by ectoprocts is called "upstream collecting", as food particles are captured before they pass through the field of cilia that creates the feeding current. This method is also used by phoronids , brachiopods and pterobranchs . The lophophore and mouth are mounted on
21150-461: The test at the aboral pole is a membrane, the periproct , which surrounds the anus . The periproct contains a variable number of hard plates, five of which, the genital plates, contain the gonopores, and one is modified to contain the madreporite , which is used to balance the water vascular system. The mouth of most sea urchins is made up of five calcium carbonate teeth or plates, with a fleshy, tongue-like structure within. The entire chewing organ
21300-404: The tips of the tentacles may check for signs of danger before the invert and lophophore are fully extended. Extension is driven by an increase in internal fluid pressure, which species with flexible exoskeletons produce by contracting circular muscles that lie just inside the body wall, while species with a membranous sac use circular muscles to squeeze this. Some species with rigid exoskeletons have
21450-587: The upper Triassic, their numbers increased again. Cidaroids have changed very little since the Late Triassic , and are the only Paleozoic echinoid group to have survived. The euechinoids diversified into new lineages in the Jurassic and Cretaceous periods, and from them emerged the first irregular echinoids (the Atelostomata ) during the early Jurassic. Some echinoids, such as Micraster in
21600-548: The water by means of a lophophore , a "crown" of hollow tentacles. Bryozoans form colonies consisting of clones called zooids that are typically about 0.5 mm ( 1 ⁄ 64 in) long. Phoronids resemble bryozoan zooids but are 2 to 20 cm (1 to 8 in) long and, although they often grow in clumps, do not form colonies consisting of clones. Brachiopods, generally thought to be closely related to bryozoans and phoronids, are distinguished by having shells rather like those of bivalves . All three of these phyla have
21750-583: The wave-battered coastal waters inhabited by many modern echinoids. Echinoids declined to near extinction at the end of the Paleozoic era, with just six species known from the Permian period. Only two lineages survived this period's massive extinction and into the Triassic : the genus Miocidaris , which gave rise to modern cidaroida (pencil urchins), and the ancestor that gave rise to the euechinoids . By
21900-421: The way invertebrates with true exoskeletons do, instead the plates forming the test grow as the animal does. The test is rigid, and divides into five ambulacral grooves separated by five wider interambulacral areas. Each of these ten longitudinal columns consists of two sets of plates (thus comprising 20 columns in total). The ambulacral plates have pairs of tiny holes through which the tube feet extend. All of
22050-507: The zooids are fully grown. Colony lifespans range from one to about 12 years, and the short-lived species pass through several generations in one season. Species that produce defensive zooids do so only when threats have already appeared, and may do so within 48 hours. The theory of "induced defenses" suggests that production of defenses is expensive and that colonies which defend themselves too early or too heavily will have reduced growth rates and lifespans. This "last minute" approach to defense
22200-416: Was coined in 1866 by Ernst Haeckel from the Greek phylon ( φῦλον , "race, stock"), related to phyle ( φυλή , "tribe, clan"). Haeckel noted that species constantly evolved into new species that seemed to retain few consistent features among themselves and therefore few features that distinguished them as a group ("a self-contained unity"): "perhaps such a real and completely self-contained unity
22350-576: Was found to be Oncousoecia lobulata . This interpretation stabilizes Oncousoecia by establishing a type species that corresponds to the general usage of the genus. Fellow Oncousoeciid Eurystrotos is now believed to be not conspecific with O. lobulata , as previously suggested, but shows enough similarities to be considered a junior synonym of Oncousoecia . Microeciella suborbicularus has also been recently distinguished from O. lobulata and O. dilatans , using this modern method of low vacuum scanning, with which it has been inaccurately synonymized with in
22500-480: Was originally called "Polyzoa", but this name was eventually replaced by Ehrenberg's term "Bryozoa". The name "Bryozoa" was originally applied only to the animals also known as Ectoprocta ( lit. ' outside-anus ' ), in which the anus lies outside the "crown" of tentacles. After the discovery of the Entoprocta ( lit. ' inside-anus ' ), in which the anus lies within a "crown" of tentacles,
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