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78-444: The palate ( / ˈ p æ l ɪ t / ) is the roof of the mouth in humans and other mammals . It separates the oral cavity from the nasal cavity . A similar structure is found in crocodilians , but in most other tetrapods , the oral and nasal cavities are not truly separated. The palate is divided into two parts, the anterior, bony hard palate and the posterior, fleshy soft palate (or velum). The maxillary nerve branch of

156-420: A megadrile earthworm into one of its taxonomic families under suborders Lumbricina and Moniligastrida is based on such features as the makeup of the clitellum, the location and disposition of the sex features (pores, prostatic glands, etc.), number of gizzards, and body shape. Currently, over 6,000 species of terrestrial earthworms are named, as provided in a species name database, but the number of synonyms

234-438: A ventral nerve cord . Earthworms' brains consist of a pair of pear-shaped cerebral ganglia. These are located in the dorsal side of the alimentary canal in the third segment, in a groove between the buccal cavity and pharynx . A pair of circum-pharyngeal connectives from the brain encircle the pharynx and then connect with a pair of sub-pharyngeal ganglia located below the pharynx in the fourth segment. This arrangement means

312-466: A "pressure" response as well as (often) a response to the dehydrating quality of the salt on human skin (toxic to earthworms), stimulates the subepidermal nerve plexus which connects to the intermuscular plexus and causes the longitudinal muscles to contract. This causes the writhing movements observed when a human picks up an earthworm. This behaviour is a reflex and does not require the CNS; it occurs even if

390-436: A bisected specimen in certain species. Gates's reports included: An unidentified Tasmanian earthworm shown growing a replacement head has been reported. Within the world of taxonomy, the stable 'Classical System' of Michaelsen (1900) and Stephenson (1930) was gradually eroded by the controversy over how to classify earthworms, such that Fender and McKey-Fender (1990) went so far as to say, "The family-level classification of

468-462: A crucial role in attracting a partner and in facilitating outcrossing. Outcrossing would provide the benefit of masking the expression of deleterious recessive mutations in progeny (see Complementation ). Copulation and reproduction are separate processes in earthworms. The mating pair overlap front ends ventrally and each exchanges sperm with the other. The clitellum becomes very reddish to pinkish in colour. Sometime after copulation, long after

546-438: A double transport system made of coelomic fluid that moves within the fluid-filled coelom and a simple, closed circulatory system , and respire (breathe) via cutaneous respiration . As soft-bodied invertebrates, they lack a true skeleton , but their structure is maintained by fluid-filled coelom chambers that function as a hydrostatic skeleton . Earthworms have a central nervous system consisting of two ganglia above

624-429: A mouth and a one-way gut. Some modern invertebrates still have such a system: food being ingested through the mouth, partially broken down by enzymes secreted in the gut, and the resulting particles engulfed by the other cells in the gut lining. Indigestible waste is ejected through the mouth. In animals at least as complex as an earthworm , the embryo forms a dent on one side, the blastopore , which deepens to become

702-419: A mouth, buccal cavity (generally running through the first one or two segments of the earthworm), pharynx (running generally about four segments in length), esophagus, crop, gizzard (usually), and intestine. Food enters at the mouth. The pharynx acts as a suction pump; its muscular walls draw in food. In the pharynx, the pharyngeal glands secrete mucus . Food moves into the esophagus , where calcium (from

780-407: A nasofrontal hinge allowing the beak to open wider than would otherwise be possible. The exterior surface of beaks is composed of a thin, horny sheath of keratin . Nectar feeders such as hummingbirds have specially adapted brushy tongues for sucking up nectar from flowers. In mammals, the buccal cavity is typically roofed by the hard and soft palates , floored by the tongue and surrounded by

858-431: A pair of commissurals running along the posterior surface of the septum. The pumping action on the dorsal vessel moves the blood forward, while the other four longitudinal vessels carry the blood rearward. In segments seven through eleven, a pair of aortic arches ring the coelom and acts as hearts, pumping the blood to the ventral vessel that acts as the aorta. The blood consists of ameboid cells and haemoglobin dissolved in

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936-542: A pair of pallial blood vessels that connect the dorsal to the subneural blood vessels. Many earthworms can eject coelomic fluid through pores in the back in response to stress; the Australian Didymogaster sylvaticus (known as the "blue squirter earthworm") can squirt fluid as high as 30 cm (12 in). The CNS consists of a bilobed brain (cerebral ganglia , or supra-pharyngeal ganglion), sub-pharyngeal ganglia, circum-pharyngeal connectives and

1014-458: A range of mouthparts suited to their mode of feeding. These include mandibles, maxillae and labium and can be modified into suitable appendages for chewing, cutting, piercing, sponging and sucking. Decapods have six pairs of mouth appendages, one pair of mandibles, two pairs of maxillae and three of maxillipeds . Sea urchins have a set of five sharp calcareous plates, which are used as jaws and are known as Aristotle's lantern . In vertebrates,

1092-550: A two-opening gut tube with a mouth at one end and an anus at the other. Which end forms first in ontogeny is a criterion used to classify bilaterian animals into protostomes and deuterostomes . In the first multicellular animals , there was probably no mouth or gut and food particles were engulfed by the cells on the exterior surface by a process known as endocytosis . The particles became enclosed in vacuoles into which enzymes were secreted and digestion took place intracellularly . The digestive products were absorbed into

1170-437: Is also used to feel and chemically sense the worm's surroundings. Some species of earthworm can even use the prehensile prostomium to grab and drag items such as grasses and leaves into their burrow. An adult earthworm develops a belt-shaped glandular swelling, called the clitellum , which covers several segments toward the front part of the animal. This is part of the reproductive system and produces egg capsules. The posterior

1248-428: Is most commonly cylindrical like the rest of the body, but depending on the species, it may also be quadrangular, octagonal, trapezoidal, or flattened. The last segment is called the periproct ; the earthworm's anus, a short vertical slit, is found on this segment. The exterior of an individual segment is a thin cuticle over the skin, commonly pigmented red to brown, which has specialized cells that secrete mucus over

1326-441: Is necessary to stimulate reproduction, even though no male genetic material passes to the offspring. Earthworm mating occurs on the surface, most often at night. Earthworms are hermaphrodites ; that is, they have both male and female sexual organs. The sexual organs are located in segments 9 to 15. Earthworms have one or two pairs of testes contained within sacs. The two or four pairs of seminal vesicles produce, store and release

1404-542: Is unknown. The families, with their known distributions or origins: From a total of around 7,000 species, only about 150 species are widely distributed around the world. These are the peregrine or cosmopolitan earthworms. Of the 182 taxa of earthworms found in the United States and Canada, 60 (33%) are introduced species. Earthworms are classified into three main ecophysiological categories: (1) leaf litter - or compost-dwelling worms that are nonburrowing, live at

1482-445: The archenteron , the first phase in the formation of the gut . In deuterostomes, the blastopore becomes the anus while the gut eventually tunnels through to make another opening, which forms the mouth. In the protostomes, it used to be thought that the blastopore formed the mouth ( proto– meaning "first") while the anus formed later as an opening made by the other end of the gut. More recent research, however, shows that in protostomes

1560-466: The cheeks , salivary glands , and upper and lower teeth . The upper teeth are embedded in the upper jaw and the lower teeth in the lower jaw , which articulates with the temporal bones of the skull . The lips are soft and fleshy folds which shape the entrance into the mouth. The buccal cavity empties through the pharynx into the oesophagus . Crocodilians living in the tropics can gape with their mouths to provide cooling by evaporation from

1638-498: The megascolecid earthworms is in chaos." Over the years, many scientists have developed their own classification systems for earthworms, which led to confusion, and these systems have been and still continue to be revised and updated. The classification system used here which was developed by Blakemore (2000), is a modern reversion to the Classical System that is historically proven and widely accepted. Categorization of

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1716-528: The microdriles ("small worms") in the semiaquatic families Tubificidae , Lumbricidae and Enchytraeidae . The megadriles are characterized by a distinct clitellum (more extensive than that of microdriles) and a vascular system with true capillaries . Earthworms are commonly found in moist, compost -rich soil, eating a wide variety of organic matters , which include detritus , living protozoa , rotifers , nematodes , bacteria , fungi and other microorganisms . An earthworm's digestive system runs

1794-619: The mouth , one on either side, connected to an axial nerve running along its length to motor neurons and sensory cells in each segment. Large numbers of chemoreceptors concentrate near its mouth. Circumferential and longitudinal muscles edging each segment let the worm move. Similar sets of muscles line the gut tube , and their actions propel digested food toward the worm's anus . Earthworms are hermaphrodites : each worm carries male and female reproductive organs and genital pores . When mating, two individual earthworms will exchange sperm and fertilize each other's ova . Depending on

1872-420: The syrinx . For each burst of song, the bird opens its beak and closes it again afterwards. The beak may move slightly and may contribute to the resonance but the song originates elsewhere. Earthworm An earthworm is a soil -dwelling terrestrial invertebrate that belongs to the phylum Annelida . The term is the common name for the largest members of the class (or subclass , depending on

1950-430: The trigeminal nerve supplies sensory innervation to the palate. The hard palate forms before birth. If the fusion is incomplete, a cleft palate results. When functioning in conjunction with other parts of the mouth, the palate produces certain sounds, particularly velar , palatal , palatalized , postalveolar , alveolopalatal , and uvular consonants . The English synonyms palate and palatum, and also

2028-447: The ability to regenerate lost segments, but this ability varies between species and depends on the extent of the damage. Stephenson (1930) devoted a chapter of his monograph to this topic, while G. E. Gates spent 20 years studying regeneration in a variety of species. But "because little interest was shown", Gates (1972) published only a few of his findings. These nevertheless show it is theoretically possible to grow two whole worms from

2106-407: The airflow from the lungs in different ways and changes the mouth's resonating properties, producing a range of different sounds. In frogs, the sounds can be amplified using sacs in the throat region. The vocal sacs can be inflated and deflated and act as resonators to transfer the sound to the outside world. A bird's song is produced by the flow of air over a vocal organ at the base of the trachea ,

2184-588: The author) Oligochaeta . In classical systems, they were in the order of Opisthopora since the male pores opened posterior to the female pores, although the internal male segments are anterior to the female. Theoretical cladistic studies have placed them in the suborder Lumbricina of the order Haplotaxida , but this may change. Other slang names for earthworms include "dew-worm", "rainworm", "nightcrawler", and "angleworm" (from its use as angling hookbaits ). Larger terrestrial earthworms are also called megadriles (which translates to "big worms") as opposed to

2262-553: The average lifespan under field conditions is four to eight years, while most garden varieties live only one to two years. Several common earthworm species are mostly parthenogenetic , meaning that growth and development of embryos happens without fertilization . Among lumbricid earthworms, parthenogenesis arose from sexual relatives many times. Parthenogenesis in some Aporrectodea trapezoides lineages arose 6.4 to 1.1 million years ago from sexual ancestors. A few species exhibit pseudogamous parthogenesis, meaning that mating

2340-472: The banks of the 4,350 km (2,703 mi) Mekong River in Southeast Asia. From front to back, the basic shape of the earthworm is a cylindrical tube-in-a-tube, divided into a series of segments (called metameres ) that compartmentalize the body. Furrows are generally externally visible on the body demarking the segments; dorsal pores and nephridiopores exude a fluid that moistens and protects

2418-564: The blood and ingested from previous meals) is pumped in to maintain proper blood calcium levels in the blood and food pH . From there the food passes into the crop and gizzard. In the gizzard , strong muscular contractions grind the food with the help of mineral particles ingested along with the food. Once through the gizzard, food continues through the intestine for digestion. The intestine secretes pepsin to digest proteins, amylase to digest polysaccharides, cellulase to digest cellulose, and lipase to digest fats. Earthworms use, in addition to

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2496-411: The bodies of their mates. Generally, within a species, the number of segments found is consistent across specimens, and individuals are born with the number of segments they will have throughout their lives. The first body segment (segment number 1) features both the earthworm's mouth and, overhanging the mouth, a fleshy lobe called the prostomium , which seals the entrance when the worm is at rest, but

2574-758: The body ( peristalsis ). The shortened part is anchored to the surrounding soil by tiny clawlike bristles ( setae ) set along its segmented length. In all the body segments except the first, last and clitellum, there is a ring of S-shaped setae embedded in the epidermal pit of each segment (perichaetine). The whole burrowing process is aided by the secretion of lubricating mucus. As a result of their movement through their lubricated tunnels, worms can make gurgling noises underground when disturbed. Earthworms move through soil by expanding crevices with force; when forces are measured according to body weight, hatchlings can push 500 times their own body weight whereas large adults can push only 10 times their own body weight. Earthworms have

2652-435: The body and are therefore considered one giant axon. The sympathetic nervous system consists of nerve plexuses in the epidermis and alimentary canal. (A plexus is a web of connected nerve cells.) The nerves that run along the body wall pass between the outer circular and inner longitudinal muscle layers of the wall. They give off branches that form the intermuscular plexus and the subepidermal plexus. These nerves connect with

2730-414: The body, but in reverse order—an inner circular layer within an outer longitudinal layer. Earthworms have a dual circulatory system in which both the coelomic fluid and a closed circulatory system carry the food, waste, and respiratory gases. The closed circulatory system has five main blood vessels: the dorsal (top) vessel, which runs above the digestive tract; the ventral (bottom) vessel, which runs below

2808-401: The brain, sub-pharyngeal ganglia and the circum-pharyngeal connectives form a nerve ring around the pharynx. The ventral nerve cord (formed by nerve cells and nerve fibers) begins at the sub-pharyngeal ganglia and extends below the alimentary canal to the most posterior body segment. The ventral nerve cord has a swelling, or ganglion, in each segment, i.e. a segmental ganglion, which occurs from

2886-547: The cavity and it can gape widely enough to accommodate large prey items. Food passes first into a pharynx and digestion occurs extracellularly in the gastrovascular cavity . Annelids have simple tube-like guts, and the possession of an anus allows them to separate the digestion of their foodstuffs from the absorption of the nutrients. Many molluscs have a radula , which is used to scrape microscopic particles off surfaces. In invertebrates with hard exoskeletons, various mouthparts may be involved in feeding behaviour. Insects have

2964-444: The coelom fluid from a forward segment is drawn in by the beating of cilia of the nephrostome . From there it is carried through the septum (wall) via a tube which forms a series of loops entwined by blood capillaries that also transfer waste into the tubule of the nephrostome. The excretory wastes are then finally discharged through a pore on the worm's side. Earthworms have no special respiratory organs. Gases are exchanged through

3042-432: The coelomic fluid to pass between segments. A pair of structures called nephrostomes are located at the back of each septum; a nephric tubule leads from each nephrostome through the septum and into the following segment. This tubule then leads to the main body fluid filtering organ, the nephridium or metanephridium, which removes metabolic waste from the coelomic fluid and expels it through pores called nephridiopores on

3120-430: The cricopharyngeal connective. On the surface, crawling speed varies both within and among individuals. Earthworms crawl faster primarily by taking longer "strides" and a greater frequency of strides. Larger Lumbricus terrestris worms crawl at a greater absolute speed than smaller worms. They achieve this by taking slightly longer strides but with slightly lower stride frequencies. Touching an earthworm, which causes

3198-509: The cuticle to keep the body moist and ease movement through the soil. Under the skin is a layer of nerve tissue, and two layers of muscles—a thin outer layer of circular muscle, and a much thicker inner layer of longitudinal muscle. Interior to the muscle layer is a fluid-filled chamber called a coelom that by its pressurization provides structure to the worm's boneless body. The segments are separated from each other by septa (the plural of "septum") which are perforated transverse walls, allowing

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3276-566: The cytoplasm and diffused into other cells. This form of digestion is used nowadays by simple organisms such as Amoeba and Paramecium and also by sponges which, despite their large size, have no mouth or gut and capture their food by endocytosis. However, most animals have a mouth and a gut, the lining of which is continuous with the epithelial cells on the surface of the body. A few animals which live parasitically originally had guts but have secondarily lost these structures. The original gut of diploblastic animals probably consisted of

3354-428: The digestive proteins, a class of surface active compounds called drilodefensins , which help digest plant material. Instead of being coiled like a mammalian intestine, in the earthworm's intestine a large mid-dorsal, tongue-like fold is present, called a typhlosole , with many folds running along its length, increasing its surface area to increase nutrient absorption. The intestine has its own pair of muscle layers like

3432-438: The digestive tract; the subneural vessel, which runs below the ventral nerve cord; and two lateroneural vessels on either side of the nerve cord. The dorsal vessel is mainly a collecting structure in the intestinal region. It receives a pair commissural and dorsal intestines in each segment. The ventral vessel branches off to a pair of ventro-tegumentaries and ventro-intestinals in each segment. The subneural vessel also gives out

3510-476: The earthworm to very quickly retreat (perhaps contracting into its burrow to escape a bird). The presence of a nervous system is essential for an animal to be able to experience nociception or pain . However, other physiological capacities are also required such as opioid sensitivity and central modulation of responses by analgesics. Enkephalin and α-endorphin -like substances have been found in earthworms. Injections of naloxone (an opioid antagonist) inhibit

3588-475: The edges of the slit-like blastopore close up in the middle, leaving openings at both ends that become the mouth and anus. Apart from sponges and placozoans , almost all animals have an internal gut cavity, which is lined with gastrodermal cells. In less advanced invertebrates such as the sea anemone , the mouth also acts as an anus. Circular muscles around the mouth are able to relax or contract in order to open or close it. A fringe of tentacles thrusts food into

3666-430: The epithelium of the buccal chamber. These receptors are gustatory and olfactory (related to taste and smell). They also respond to chemical stimuli. (Chemoreceptor) The gut of the earthworm is a straight tube that extends from the worm's mouth to its anus . It is differentiated into an alimentary canal and associated glands which are embedded in the wall of the alimentary canal itself. The alimentary canal consists of

3744-403: The escape responses of earthworms. This indicates that opioid substances play a role in sensory modulation, similar to that found in many vertebrates. Although some worms have eyes , earthworms do not. However, they do have specialized photosensitive cells called "light cells of Hess". These photoreceptor cells have a central intracellular cavity ( phaosome ) filled with microvilli . As well as

3822-422: The fastest, from the rear to the front of the animal. If the rear of the worm is touched, a signal is rapidly sent forwards causing the longitudinal muscles in each segment to contract. This causes the worm to shorten very quickly as an attempt to escape from a predator or other potential threat. The two medial giant axons connect with each other and send signals from the front to the rear. Stimulation of these causes

3900-482: The fifth to the last segment of the body. There are also three giant axons , one medial giant axon (MGA) and two lateral giant axons (LGAs) on the mid-dorsal side of the ventral nerve cord. The MGA is 0.07 mm in diameter and transmits in an anterior-posterior direction at a rate of 32.2 m/s. The LGAs are slightly narrower at 0.05 mm in diameter and transmit in a posterior-anterior direction at 12.6 m/s. The two LGAs are connected at regular intervals along

3978-473: The first part of the digestive system is the buccal cavity , commonly known as the mouth. The buccal cavity of a fish is separated from the opercular cavity by the gills . Water flows in through the mouth, passes over the gills and exits via the operculum or gill slits . Nearly all fish have jaws and may seize food with them but most feed by opening their jaws, expanding their pharynx and sucking in food items. The food may be held or chewed by teeth located in

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4056-401: The first three and the last ones. The three types of nephridia are: integumentary, septal, and pharyngeal. The integumentary nephridia lie attached to the inner side of the body wall in all segments except the first two. The septal nephridia are attached to both sides of the septa behind the 15th segment. The pharyngeal nephridia are attached to the fourth, fifth and sixth segments. The waste in

4134-433: The jaws, on the roof of the mouth, on the pharynx or on the gill arches . Nearly all amphibians are carnivorous as adults. Many catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the mouth, where they hold the prey with their jaws. They then swallow their food whole without much chewing. They typically have many small hinged pedicellate teeth , the bases of which are attached to

4212-755: The jaws, while the crowns break off at intervals and are replaced. Most amphibians have one or two rows of teeth in both jaws but some frogs lack teeth in the lower jaw. In many amphibians, there are also vomerine teeth attached to the bone in the roof of the mouth. The mouths of reptiles are largely similar to those of mammals. The crocodilians are the only reptiles to have teeth anchored in sockets in their jaws. They are able to replace each of their approximately 80 teeth up to 50 times during their lives. Most reptiles are either carnivorous or insectivorous, but turtles are often herbivorous. Lacking teeth that are suitable for efficiently chewing of their food, turtles often have gastroliths in their stomach to further grind

4290-445: The length of its body. They are one of nature's most important detritivores and coprophages , and also serve as food for many low-level consumers within the ecosystems. Earthworms exhibit an externally segmented tube-within-a-tube body plan with corresponding internal segmentations, and usually have setae on all segments. They have a cosmopolitan distribution wherever soil, water and temperature conditions allow. They have

4368-405: The mechanism for producing sounds for communication. To produce sounds, air is forced from the lungs over vocal cords in the larynx. In humans, the pharynx, soft palate, hard palate, alveolar ridge , tongue, teeth and lips are termed articulators and play their part in the production of speech . Varying the position of the tongue in relation to the other articulators or moving the lips restricts

4446-449: The microvilli, there are several sensory cilia in the phaosome which are structurally independent of the microvilli. The photoreceptors are distributed in most parts of the epidermis, but are more concentrated on the back and sides of the worm. A relatively small number occur on the ventral surface of the first segment. They are most numerous in the prostomium, and reduce in density in the first three segments; they are very few in number past

4524-418: The mineral soil. Because a high level of organic matter mixing is associated with soil fertility , an abundance of earthworms is generally considered beneficial by farmers and gardeners. As long ago as 1881 Charles Darwin wrote: "It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures." Also, while, as

4602-414: The moist skin and capillaries, where the oxygen is picked up by the haemoglobin dissolved in the blood plasma and carbon dioxide is released. Water, as well as salts, can also be moved through the skin by active transport. At birth, earthworms emerge small but fully formed, lacking only their sex structures which develop in about 60 to 90 days. They attain full size in about one year. Scientists predict that

4680-419: The mouth lining. Some mammals rely on panting for thermoregulation as it increases evaporation of water across the moist surfaces of the lungs, the tongue and mouth. Birds also avoid overheating by gular fluttering, flapping the wings near the gular (throat) skin, similar to panting in mammals. Various animals use their mouths in threat displays. They may gape widely, exhibit their teeth prominently, or flash

4758-591: The name suggests, the main habitat of earthworms is in soil, they are not restricted to this habitat. The brandling worm Eisenia fetida lives in decaying plant matter and manure. Arctiostrotus vancouverensis from Vancouver Island and the Olympic Peninsula is generally found in decaying conifer logs. Aporrectodea limicola , Sparganophilus spp., and several others are found in mud in streams. Some species are arboreal, some aquatic and some euryhaline (salt-water tolerant) and littoral (living on

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4836-420: The nerve cord is removed. Each segment of the earthworm has its own nerve plexus. The plexus of one segment is not connected directly to that of adjacent segments. The nerve cord is required to connect the nervous systems of the segments. The giant axons carry the fastest signals along the nerve cord. These are emergency signals that initiate reflex escape behaviours. The larger dorsal giant axon conducts signals

4914-614: The numbers of worms that go into diapause . The more acidic the soil, the sooner worms go into diapause, and remain in diapause the longest time at a pH of 6.4. Earthworms are preyed upon by many species of birds (e.g. robins, starlings , thrushes , gulls , crows ), snakes, wood turtles, mammals (e.g. bears , boars, foxes , hedgehogs , pigs , moles ) and invertebrates (e.g. ants , flatworms , ground beetles and other beetles , snails , spiders , and slugs ). Earthworms have many internal parasites , including protozoa , platyhelminthes, mites, and nematodes ; they can be found in

4992-437: The other way round. As the roof of the mouth was once considered the seat of the sense of taste , palate can also refer to this sense itself, as in the phrase "a discriminating palate". By further extension, the flavor of a food (particularly beer or wine) may be called its palate, as when a wine is said to have an oaky palate. Mouth Most bilaterian phyla , including arthropods , molluscs and chordates , have

5070-517: The plant material. Snakes have a very flexible lower jaw, the two halves of which are not rigidly attached, and numerous other joints in their skull. These modifications allow them to open their mouths wide enough to swallow their prey whole, even if it is wider than they are. Birds do not have teeth, relying instead on other means of gripping and macerating their food. Their beaks have a range of sizes and shapes according to their diet and are composed of elongated mandibles. The upper mandible may have

5148-433: The plasma. The second circulatory system derives from the cells of the digestive system that line the coelom. As the digestive cells become full, they release non-living cells of fat into the fluid-filled coelom, where they float freely but can pass through the walls separating each segment, moving food to other parts and assist in wound healing. The excretory system contains a pair of nephridia in every segment, except for

5226-590: The related adjective palatine (as in palatine bone ), are all from the Latin palatum via Old French palat , words that like their English derivatives , refer to the "roof" of the mouth. The Latin word palatum is of unknown (possibly Etruscan ) ultimate origin and served also as a source to the Latin word meaning palace, palatium , from which other senses of palatine and the English word palace derive, and not

5304-793: The rest. As the worm slips out of the ring, the ends of the cocoon seal to form a vaguely onion-shaped incubator ( cocoon ) in which the embryonic worms develop. Hence fertilization is external. The cocoon is then deposited in the soil. After three weeks, 2 to 20 offspring hatch with an average of four. Development is direct i.e. without formation of any larva. Exposure of the earthworm Eisenia fetida to ionizing radiation induced DNA strand breaks and oxidized DNA bases . These DNA damages could then be repaired in somatic and spermatogenic cells. Earthworms testis cells are also capable of repairing hydrogen peroxide induced oxidative DNA adducts. Earthworms travel underground by means of waves of muscular contractions which alternately shorten and lengthen

5382-500: The soil, such as temperature, moisture, pH, salts, aeration , and texture, as well as available food, and the ability of the species to reproduce and disperse. One of the most important environmental factors is pH , but earthworms vary in their preferences. Most favour neutral to slightly acidic soils. Lumbricus terrestris is still present in a pH of 5.4, Dendrobaena octaedra at a pH of 4.3 and some Megascolecidae are present in extremely acidic humic soils. Soil pH may also influence

5460-549: The soil-litter interface and eat decomposing organic matter ( epigeic ) e.g. Eisenia fetida ; (2) topsoil- or subsoil-dwelling worms that feed (on soil), burrow and cast within the soil, creating horizontal burrows in upper 10–30  cm of soil ( endogeic ); and (3) worms that construct permanent deep vertical burrows which they use to visit the surface to obtain plant material for food, such as leaves ( anecic , meaning "reaching up"), e.g. Lumbricus terrestris . Earthworm populations depend on both physical and chemical properties of

5538-404: The species, an adult earthworm can be from 10 mm (0.39 in) long and 1 mm (0.039 in) wide to 3 m (9.8 ft) long and over 25 mm (0.98 in) wide, but the typical Lumbricus terrestris grows to about 360 mm (14 in) long. Probably the longest worm on confirmed records is Amynthas mekongianus that extends up to 3 m (10 ft) in the mud along

5616-838: The sperm via the male pores. Ovaries and oviducts in segment 13 release eggs via female pores on segment 14, while sperm is expelled from segment 15. One or more pairs of spermathecae are present in segments 9 and 10 (depending on the species) which are internal sacs that receive and store sperm from the other worm during copulation. As a result, segment 15 of one worm exudes sperm into segments 9 and 10 with its storage vesicles of its mate. Some species use external spermatophores for sperm transfer. In Hormogaster samnitica and Hormogaster elisae transcriptome DNA libraries were sequenced and two sex pheromones , Attractin and Temptin, were detected in all tissue samples of both species . Sex pheromones are probably important in earthworms because they live in an environment where chemical signaling may play

5694-419: The startling colours of the mouth lining. This display allows each potential combatant an opportunity to assess the weapons of their opponent and lessens the likelihood of actual combat being necessary. A number of species of bird use a gaping , open beak in their fear and threat displays. Some augment the display by hissing or breathing heavily, while others clap their beaks. Mouths are also used as part of

5772-565: The third segment. These receptors are abundant and distributed all over the epidermis . Each receptor shows a slightly elevated cuticle which covers a group of tall, slender and columnar receptor cells. These cells bear small hairlike processes at their outer ends and their inner ends are connected with nerve fibres. The epidermal receptors are tactile in function. They are also concerned with changes in temperature and respond to chemical stimuli. Earthworms are extremely sensitive to touch and mechanical vibration. These receptors are located only in

5850-406: The worm's sides; usually, two nephridia (sometimes more) are found in most segments. At the centre of a worm is the digestive tract , which runs straight through from mouth to anus without coiling, and is flanked above and below by blood vessels (the dorsal blood vessel and the ventral blood vessel as well as a subneural blood vessel) and the ventral nerve cord , and is surrounded in each segment by

5928-413: The worm's surface, allowing it to breathe. Except for the mouth and anal segments, each segment carries bristlelike hairs called lateral setae used to anchor parts of the body during movement; species may have four pairs of setae on each segment or more than eight sometimes forming a complete circle of setae per segment. Special ventral setae are used to anchor mating earthworms by their penetration into

6006-420: The worms have separated, the clitellum (behind the spermathecae) secretes material which forms a ring around the worm. The worm then backs out of the ring, and as it does so, it injects its own eggs and the other worm's sperm into it. Thus each worm becomes the genetic father of some of their offspring (due to its own sperm transferred to other earthworm) and the genetic mother (offsprings from its own egg cells) of

6084-432: The worms' blood , seminal vesicles , coelom , or intestine , or in their cocoons (e.g. the mite Histiostoma murchiei is a parasite of earthworm cocoons ). The earthworm activity aerates and mixes the soil, and is conducive to mineralization of nutrients and their uptake by vegetation. Certain species of earthworm come to the surface and graze on the higher concentrations of organic matter present there, mixing it with

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