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63-552: The Drawa flows across regions including Pojezierze Drawskie , Równina Drawska and partly near Pojezierze Wałeckie and Kotlina Gorzowska . The source of the Drawa is in nature reserve Dolina Pięciu Jezior . Then, the river flows across Drawski Landscape Park , Drawieński National Park and Drawski forest . The section from Czaplinek to Noteć is called the Karol Wojtyła Silver Route . The biggest tributaries of

126-531: A chemical that stops movement of other cells in the affected area, thus preventing the intruder from using the sponge's internal transport systems. If the intrusion persists, the grey cells concentrate in the area and release toxins that kill all cells in the area. The "immune" system can stay in this activated state for up to three weeks. Sponges have three asexual methods of reproduction: after fragmentation, by budding , and by producing gemmules . Fragments of sponges may be detached by currents or waves. They use

189-445: A few carnivorous sponges have lost these water flow systems and the choanocytes. All known living sponges can remold their bodies, as most types of their cells can move within their bodies and a few can change from one type to another. Even if a few sponges are able to produce mucus – which acts as a microbial barrier in all other animals – no sponge with the ability to secrete a functional mucus layer has been recorded. Without such

252-423: A mucus layer their living tissue is covered by a layer of microbial symbionts, which can contribute up to 40–50% of the sponge wet mass. This inability to prevent microbes from penetrating their porous tissue could be a major reason why they have never evolved a more complex anatomy. Like cnidarians (jellyfish, etc.) and ctenophores (comb jellies), and unlike all other known metazoans, sponges' bodies consist of

315-542: A non-living jelly-like mass ( mesohyl ) sandwiched between two main layers of cells. Cnidarians and ctenophores have simple nervous systems, and their cell layers are bound by internal connections and by being mounted on a basement membrane (thin fibrous mat, also known as " basal lamina "). Sponges do not have a nervous system similar to that of vertebrates but may have one that is quite different. Their middle jelly-like layers have large and varied populations of cells, and some types of cells in their outer layers may move into

378-876: A root-like base. Sponges are more abundant but less diverse in temperate waters than in tropical waters, possibly because organisms that prey on sponges are more abundant in tropical waters. Glass sponges are the most common in polar waters and in the depths of temperate and tropical seas, as their very porous construction enables them to extract food from these resource-poor waters with the minimum of effort. Demosponges and calcareous sponges are abundant and diverse in shallower non-polar waters. The different classes of sponge live in different ranges of habitat: Sponges with photosynthesizing endosymbionts produce up to three times more oxygen than they consume, as well as more organic matter than they consume. Such contributions to their habitats' resources are significant along Australia's Great Barrier Reef but relatively minor in

441-644: A study in 2007 found no evidence of this and concluded that they extract bacteria and other micro-organisms from water very efficiently (about 79%) and process suspended sediment grains to extract such prey. Collar bodies digest food and distribute it wrapped in vesicles that are transported by dynein "motor" molecules along bundles of microtubules that run throughout the syncytium . Sponges' cells absorb oxygen by diffusion from water into cells as water flows through body, into which carbon dioxide and other soluble waste products such as ammonia also diffuse. Archeocytes remove mineral particles that threaten to block

504-471: A third of the total mass of living tissue in some sponges, and some sponges gain 48% to 80% of their energy supply from these micro-organisms. In 2008, a University of Stuttgart team reported that spicules made of silica conduct light into the mesohyl , where the photosynthesizing endosymbionts live. Sponges that host photosynthesizing organisms are most common in waters with relatively poor supplies of food particles and often have leafy shapes that maximize

567-738: Is biomineralized . The mesohyl functions as an endoskeleton in most sponges, and is the only skeleton in soft sponges that encrust hard surfaces such as rocks. More commonly the mesohyl is stiffened by mineral spicules , by spongin fibers or both. Spicules, which are present in most but not all species, may be made of silica or calcium carbonate, and vary in shape from simple rods to three-dimensional "stars" with up to six rays. Spicules are produced by sclerocyte cells, and may be separate, connected by joints, or fused. Some sponges also secrete exoskeletons that lie completely outside their organic components. For example, sclerosponges ("hard sponges") have massive calcium carbonate exoskeletons over which

630-572: Is a neuter plural of the Modern Latin term porifer , which comes from the roots porus meaning "pore, opening", and -fer meaning "bearing or carrying". Sponges are similar to other animals in that they are multicellular , heterotrophic , lack cell walls and produce sperm cells . Unlike other animals, they lack true tissues and organs . Some of them are radially symmetrical, but most are asymmetrical. The shapes of their bodies are adapted for maximal efficiency of water flow through

693-438: Is also a place of living of the rare specimens – sea trout , common minnow , european bullhead and vimba vimba . The Drawa also hosts buzzards , red algae , sponges , spargania and potamogeton . From the 14th century, the river has been used as a navigational route. Since 1700, the Drawa has been used for drifting honey from Drawsko to Frankfurt . Navigation of the river continued until World War II . In 1974, on

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756-402: Is constant, specimens 1 m (3.3 ft) wide must be about 5,000 years old. Some sponges start sexual reproduction when only a few weeks old, while others wait until they are several years old. Adult sponges lack neurons or any other kind of nervous tissue . However, most species have the ability to perform movements that are coordinated all over their bodies, mainly contractions of

819-431: Is easiest. The fragile glass sponges , with " scaffolding " of silica spicules, are restricted to polar regions and the ocean depths where predators are rare. Fossils of all of these types have been found in rocks dated from 580  million years ago . In addition Archaeocyathids , whose fossils are common in rocks from 530 to 490 million years ago , are now regarded as a type of sponge. Although most of

882-504: Is known about how they actually capture prey, although some species are thought to use either sticky threads or hooked spicules . Most carnivorous sponges live in deep waters, up to 8,840 m (5.49 mi), and the development of deep-ocean exploration techniques is expected to lead to the discovery of several more. However, one species has been found in Mediterranean caves at depths of 17–23 m (56–75 ft), alongside

945-433: Is much greater than that of the canals, water flow through chambers slows to 3.6 cm per hour , making it easy for choanocytes to capture food. All the water is expelled through a single osculum at about 8.5 cm per second , fast enough to carry waste products some distance away. In zoology a skeleton is any fairly rigid structure of an animal, irrespective of whether it has joints and irrespective of whether it

1008-434: Is probably most common, where larvae with vertically transmitted symbionts also acquire others horizontally). There are four types of larvae, but all are lecithotrophic (non-feeding) balls of cells with an outer layer of cells whose flagella or cilia enable the larvae to move. After swimming for a few days the larvae sink and crawl until they find a place to settle. Most of the cells transform into archeocytes and then into

1071-601: Is the only skeleton in soft sponges that encrust such hard surfaces as rocks. More commonly, the mesohyl is stiffened by mineral spicules , by spongin fibers, or both. 90% of all known sponge species that have the widest range of habitats including all freshwater ones are demosponges that use spongin; many species have silica spicules, whereas some species have calcium carbonate exoskeletons . Calcareous sponges have calcium carbonate spicules and, in some species, calcium carbonate exoskeletons, are restricted to relatively shallow marine waters where production of calcium carbonate

1134-451: The epithelia of more complex animals, they are not bound tightly by cell-to-cell connections or a basal lamina (thin fibrous sheet underneath). The flexibility of these layers and re-modeling of the mesohyl by lophocytes allow the animals to adjust their shapes throughout their lives to take maximum advantage of local water currents. The simplest body structure in sponges is a tube or vase shape known as "asconoid", but this severely limits

1197-456: The genus Chondrocladia uses a highly modified water flow system to inflate balloon-like structures that are used for capturing prey. Freshwater sponges often host green algae as endosymbionts within archaeocytes and other cells and benefit from nutrients produced by the algae. Many marine species host other photosynthesizing organisms, most commonly cyanobacteria but in some cases dinoflagellates . Symbiotic cyanobacteria may form

1260-470: The mesohyl and form spermatic cysts while eggs are formed by transformation of archeocytes , or of choanocytes in some species. Each egg generally acquires a yolk by consuming "nurse cells". During spawning, sperm burst out of their cysts and are expelled via the osculum . If they contact another sponge of the same species, the water flow carries them to choanocytes that engulf them but, instead of digesting them, metamorphose to an ameboid form and carry

1323-728: The metazoan phylum Porifera ( / p ə ˈ r ɪ f ər ə ˌ p ɔː -/ pər- IF -ər-ə, por- ; meaning 'pore bearer'), a basal animal clade and a sister taxon of the diploblasts . They are sessile filter feeders that are bound to the seabed , and are one of the most ancient members of macrobenthos , with many historical species being important reef -building organisms. Sponges are multicellular organisms consisting of jelly-like mesohyl sandwiched between two thin layers of cells , and usually have tube-like bodies full of pores and channels that allow water to circulate through them. They have unspecialized cells that can transform into other types and that often migrate between

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1386-463: The pinacocytes , squeezing the water channels and thus expelling excess sediment and other substances that may cause blockages. Some species can contract the osculum independently of the rest of the body. Sponges may also contract in order to reduce the area that is vulnerable to attack by predators. In cases where two sponges are fused, for example if there is a large but still unseparated bud, these contraction waves slowly become coordinated in both of

1449-455: The " Siamese twins ". The coordinating mechanism is unknown, but may involve chemicals similar to neurotransmitters . However, glass sponges rapidly transmit electrical impulses through all parts of the syncytium , and use this to halt the motion of their flagella if the incoming water contains toxins or excessive sediment. Myocytes are thought to be responsible for closing the osculum and for transmitting signals between different parts of

1512-611: The 1950s, though, these had been overfished so heavily that the industry almost collapsed, and most sponge-like materials are now synthetic. Sponges and their microscopic endosymbionts are now being researched as possible sources of medicines for treating a wide range of diseases. Dolphins have been observed using sponges as tools while foraging . Sponges constitute the phylum Porifera, and have been defined as sessile metazoans (multicelled immobile animals) that have water intake and outlet openings connected by chambers lined with choanocytes , cells with whip-like flagella. However,

1575-504: The Drawa are the Kokna , Korytnica , Mierzęcka Struga , Płociczna , Pokrętna , Słopica , Wąsowa . The main streams of the river are the Bagnica , Drawsko , Drawka , Głęboka , Miedzniki , Moczel , Pełknica , Radówka , Sitna , Studzienica , Sucha , Szczuczna , Wilżnica . One canal, Prostynia , flows into the Drawa. The Drawa flows through many lakes. In the upper region of

1638-511: The West Pomeranian Voivodeship signed a contract for the preparation of a protection plan for the park. This West Pomeranian Voivodeship location article is a stub . You can help Misplaced Pages by expanding it . This Polish protected area -related article is a stub . You can help Misplaced Pages by expanding it . Sponge Parazoa /Ahistozoa ( sans Placozoa ) Sponges or sea sponges are members of

1701-475: The amount of sunlight they collect. A recently discovered carnivorous sponge that lives near hydrothermal vents hosts methane-eating bacteria and digests some of them. Sponges do not have the complex immune systems of most other animals. However, they reject grafts from other species but accept them from other members of their own species. In a few marine species, gray cells play the leading role in rejection of foreign material. When invaded, they produce

1764-523: The approximately 5,000–10,000 known species of sponges feed on bacteria and other microscopic food in the water, some host photosynthesizing microorganisms as endosymbionts , and these alliances often produce more food and oxygen than they consume. A few species of sponges that live in food-poor environments have evolved as carnivores that prey mainly on small crustaceans . Most sponges reproduce sexually , but they can also reproduce asexually. Sexually reproducing species release sperm cells into

1827-1135: The banks, Wydrzy Głaz can be found ( Moczele ). On the section of the river from Lubie to Prostynia , rafting and canoeing are forbidden because the Drawski Training Ground is located in that area. Drawski Landscape Park Drawsko Landscape Park ( Drawski Park Krajobrazowy ) is a protected area ( Landscape Park ) in north-western Poland , established in 1979, covering an area of 414.3 square kilometres (160.0 sq mi). The Park lies within West Pomeranian Voivodeship : in Drawsko County ( Gmina Czaplinek , Gmina Ostrowice , Gmina Złocieniec ), Szczecinek County ( Gmina Barwice , Gmina Borne Sulinowo ) and Świdwin County ( Gmina Połczyn-Zdrój ). There are valuable landscape objects, lakes (the largest Drawsko), moraine embankments and erratic boulders. There are over 40 species of legally protected plants in

1890-418: The body. Sponges contain genes very similar to those that contain the "recipe" for the post- synaptic density, an important signal-receiving structure in the neurons of all other animals. However, in sponges these genes are only activated in "flask cells" that appear only in larvae and may provide some sensory capability while the larvae are swimming. This raises questions about whether flask cells represent

1953-477: The center. The larvae then leave their parents' bodies. The cytological progression of porifera oogenesis and spermatogenesis ( gametogenesis ) is very similar to that of other metazoa. Most of the genes from the classic set of meiotic genes, including genes for DNA recombination and double-strand break repair, that are conserved in eukaryotes are expressed in the sponges (e.g. Geodia hentscheli and Geodia phlegraei ). Since porifera are considered to be

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2016-415: The central cavity, where the water deposits nutrients and then leaves through a hole called the osculum . The single-celled choanoflagellates resemble the choanocyte cells of sponges which are used to drive their water flow systems and capture most of their food. This along with phylogenetic studies of ribosomal molecules have been used as morphological evidence to suggest sponges are the sister group to

2079-597: The cross-section area of the choanocyte-lined regions is much greater than that of the intake and outlet channels. This makes the flow slower near the choanocytes and thus makes it easier for them to trap food particles. For example, in Leuconia , a small leuconoid sponge about 10 centimetres (3.9 in) tall and 1 centimetre (0.39 in) in diameter, water enters each of more than 80,000 intake canals at 6 cm per minute . However, because Leuconia has more than 2 million flagellated chambers whose combined diameter

2142-448: The earliest divergent animals, these findings indicate that the basic toolkit of meiosis including capabilities for recombination and DNA repair were present early in eukaryote evolution. Sponges in temperate regions live for at most a few years, but some tropical species and perhaps some deep-ocean ones may live for 200 years or more. Some calcified demosponges grow by only 0.2 mm (0.0079 in) per year and, if that rate

2205-423: The fact that growth in any direction increases the number of choanocyte chambers enables them to take a wider range of forms, for example, "encrusting" sponges whose shapes follow those of the surfaces to which they attach. All freshwater and most shallow-water marine sponges have leuconid bodies. The networks of water passages in glass sponges are similar to the leuconid structure. In all three types of structure

2268-535: The first outgroup to branch off the evolutionary tree from the last common ancestor of all animals , with fossil evidence of primitive sponges such as Otavia from as early as the Tonian period (around 800  Mya ). The branch of zoology that studies sponges is known as spongiology . The term sponge derives from the Ancient Greek word σπόγγος spóngos . The scientific name Porifera

2331-412: The living tissue is suspended like a cobweb that contains most of the cell types. This tissue is a syncytium that in some ways behaves like many cells that share a single external membrane , and in others like a single cell with multiple nuclei . Most sponges work rather like chimneys : they take in water at the bottom and eject it from the osculum at the top. Since ambient currents are faster at

2394-406: The main cell layers and the mesohyl in the process. They do not have complex nervous , digestive or circulatory systems . Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes, usually via flagella movements of the so-called " collar cells ". Believed to be some of the most basal animals alive today, sponges were possibly

2457-436: The middle layer and change their functions. A sponge's body is hollow and is held in shape by the mesohyl , a jelly-like substance made mainly of collagen and reinforced by a dense network of fibers also made of collagen. 18 distinct cell types have been identified. The inner surface is covered with choanocytes , cells with cylindrical or conical collars surrounding one flagellum per choanocyte. The wave-like motion of

2520-448: The mobility of their pinacocytes and choanocytes and reshaping of the mesohyl to re-attach themselves to a suitable surface and then rebuild themselves as small but functional sponges over the course of several days. The same capabilities enable sponges that have been squeezed through a fine cloth to regenerate. A sponge fragment can only regenerate if it contains both collencytes to produce mesohyl and archeocytes to produce all

2583-434: The more usual filter-feeding sponges. The cave-dwelling predators capture crustaceans under 1 mm (0.039 in) long by entangling them with fine threads, digest them by enveloping them with further threads over the course of a few days, and then return to their normal shape; there is no evidence that they use venom . Most known carnivorous sponges have completely lost the water flow system and choanocytes . However,

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2646-442: The number of choanocytes and hence in pumping capacity enables syconoid sponges to grow up to a few centimeters in diameter. The "leuconoid" pattern boosts pumping capacity further by filling the interior almost completely with mesohyl that contains a network of chambers lined with choanocytes and connected to each other and to the water intakes and outlet by tubes. Leuconid sponges grow to over 1 m (3.3 ft) in diameter, and

2709-691: The organic matter forms a thin layer with choanocyte chambers in pits in the mineral. These exoskeletons are secreted by the pinacocytes that form the animals' skins. Although adult sponges are fundamentally sessile animals, some marine and freshwater species can move across the sea bed at speeds of 1–4 mm (0.039–0.157 in) per day, as a result of amoeba -like movements of pinacocytes and other cells. A few species can contract their whole bodies, and many can close their oscula and ostia . Juveniles drift or swim freely, while adults are stationary. Sponges do not have distinct circulatory , respiratory , digestive , and excretory systems – instead,

2772-432: The ostia, while those at the base of the animal are responsible for anchoring it. Other types of cells live and move within the mesohyl: Many larval sponges possess neuron-less eyes that are based on cryptochromes . They mediate phototaxic behavior. Glass sponges present a distinctive variation on this basic plan. Their spicules, which are made of silica , form a scaffolding -like framework between whose rods

2835-539: The ostia, transport them through the mesohyl and generally dump them into the outgoing water current, although some species incorporate them into their skeletons. In waters where the supply of food particles is very poor, some species prey on crustaceans and other small animals. So far only 137 species have been discovered. Most belong to the family Cladorhizidae , but a few members of the Guitarridae and Esperiopsidae are also carnivores. In most cases, little

2898-661: The other cell types. A very few species reproduce by budding. Gemmules are "survival pods" which a few marine sponges and many freshwater species produce by the thousands when dying and which some, mainly freshwater species, regularly produce in autumn. Spongocytes make gemmules by wrapping shells of spongin, often reinforced with spicules, round clusters of archeocytes that are full of nutrients. Freshwater gemmules may also include photosynthesizing symbionts. The gemmules then become dormant, and in this state can survive cold, drying out, lack of oxygen and extreme variations in salinity . Freshwater gemmules often do not revive until

2961-674: The park, and the avifauna consists of 148 species of breeding birds (including eagles, herons, cranes, black storks, cormorants). Among the fish there are, among others pike perch, perch, eel and whitefish. Within the Landscape Park are eight nature reserves . Since 2012, the park has been part of the Complex of Landscape Parks of the West Pomeranian Voivodeship in Szczecin. In 2020, the Landscape Parks Complex of

3024-582: The predecessors of true neurons or are evidence that sponges' ancestors had true neurons but lost them as they adapted to a sessile lifestyle. Sponges are worldwide in their distribution, living in a wide range of ocean habitats, from the polar regions to the tropics. Most live in quiet, clear waters, because sediment stirred up by waves or currents would block their pores, making it difficult for them to feed and breathe. The greatest numbers of sponges are usually found on firm surfaces such as rocks, but some sponges can attach themselves to soft sediment by means of

3087-416: The pumping capacity that supplies food and oxygen depends on the area covered by choanocytes. Asconoid sponges seldom exceed 1 mm (0.039 in) in diameter. Some sponges overcome this limitation by adopting the "syconoid" structure, in which the body wall is pleated . The inner pockets of the pleats are lined with choanocytes, which connect to the outer pockets of the pleats by ostia. This increase in

3150-648: The rest of animals. A great majority are marine (salt-water) species, ranging in habitat from tidal zones to depths exceeding 8,800 m (5.5 mi), though there are freshwater species. All adult sponges are sessile , meaning that they attach to an underwater surface and remain fixed in place (i.e., do not travel). While in their larval stage of life, they are motile . Many sponges have internal skeletons of spicules (skeletal-like fragments of calcium carbonate or silicon dioxide ), and/or spongin (a modified type of collagen protein). An internal gelatinous matrix called mesohyl functions as an endoskeleton , and it

3213-526: The river route was founded a nature reserve Drawa and in 1990 Drawieński National Park . The Drawa flows near various historical buildings. One of them is Drahimski Castle , which was turned into the museum. The castle was built in 1360 by the Order of Saint John . There are also interesting bunkers near camping in Kotlina . On Drawa's route Wedel's Castle , from the 14th century, can also be found. On one of

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3276-490: The river there are Górne , Krąg , Długie , Głębokie , Małe  [ pl ] . Further down the river, the lakes Prosino , Żerdno , Drawsko Lake , Rzepowskie , Lubie , Krosino , Wielkie and Małe Dębno can be found. The river contains over thirty species of fish, including the Rutilus , perch , gudgeon , European chub , burbot , trout , grayling , barbel , bream , spirlin and silver bream . The river

3339-468: The same species but different individuals can join forces to form one sponge. Some gemmules are retained within the parent sponge, and in spring it can be difficult to tell whether an old sponge has revived or been "recolonized" by its own gemmules. Most sponges are hermaphrodites (function as both sexes simultaneously), although sponges have no gonads (reproductive organs). Sperm are produced by choanocytes or entire choanocyte chambers that sink into

3402-402: The size of the animal. The body structure is characterized by a stalk-like spongocoel surrounded by a single layer of choanocytes. If it is simply scaled up, the ratio of its volume to surface area increases, because surface increases as the square of length or width while volume increases proportionally to the cube. The amount of tissue that needs food and oxygen is determined by the volume, but

3465-444: The sperm through the mesohyl to eggs, which in most cases engulf the carrier and its cargo. A few species release fertilized eggs into the water, but most retain the eggs until they hatch. By retaining the eggs, the parents can transfer symbiotic microorganisms directly to their offspring through vertical transmission , while the species who release their eggs into the water has to acquire symbionts horizontally (a combination of both

3528-504: The sponges, for example as temperatures drop, many freshwater species and a few marine ones produce gemmules , "survival pods" of unspecialized cells that remain dormant until conditions improve; they then either form completely new sponges or recolonize the skeletons of their parents. The few species of demosponge that have entirely soft fibrous skeletons with no hard elements have been used by humans over thousands of years for several purposes, including as padding and as cleaning tools. By

3591-399: The temperature drops, stays cold for a few months and then reaches a near-"normal" level. When a gemmule germinates, the archeocytes round the outside of the cluster transform into pinacocytes , a membrane over a pore in the shell bursts, the cluster of cells slowly emerges, and most of the remaining archeocytes transform into other cell types needed to make a functioning sponge. Gemmules from

3654-409: The top, the suction effect that they produce by Bernoulli's principle does some of the work for free. Sponges can control the water flow by various combinations of wholly or partially closing the osculum and ostia (the intake pores) and varying the beat of the flagella, and may shut it down if there is a lot of sand or silt in the water. Although the layers of pinacocytes and choanocytes resemble

3717-489: The types appropriate for their locations in a miniature adult sponge. Glass sponge embryos start by dividing into separate cells, but once 32 cells have formed they rapidly transform into larvae that externally are ovoid with a band of cilia round the middle that they use for movement, but internally have the typical glass sponge structure of spicules with a cobweb-like main syncitium draped around and between them and choanosyncytia with multiple collar bodies in

3780-670: The walls of the ostia. Bacteria-sized particles, below 0.5 micrometers, pass through the ostia and are caught and consumed by choanocytes . Since the smallest particles are by far the most common, choanocytes typically capture 80% of a sponge's food supply. Archaeocytes transport food packaged in vesicles from cells that directly digest food to those that do not. At least one species of sponge has internal fibers that function as tracks for use by nutrient-carrying archaeocytes, and these tracks also move inert objects. It used to be claimed that glass sponges could live on nutrients dissolved in sea water and were very averse to silt. However,

3843-493: The water flow system supports all these functions. They filter food particles out of the water flowing through them. Particles larger than 50 micrometers cannot enter the ostia and pinacocytes consume them by phagocytosis (engulfing and intracellular digestion). Particles from 0.5 μm to 50 μm are trapped in the ostia, which taper from the outer to inner ends. These particles are consumed by pinacocytes or by archaeocytes which partially extrude themselves through

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3906-402: The water to fertilize ova released or retained by its mate or "mother"; the fertilized eggs develop into larvae which swim off in search of places to settle. Sponges are known for regenerating from fragments that are broken off, although this only works if the fragments include the right types of cells. Some species reproduce by budding. When environmental conditions become less hospitable to

3969-458: The whip-like flagella drives water through the sponge's body. All sponges have ostia , channels leading to the interior through the mesohyl, and in most sponges these are controlled by tube-like porocytes that form closable inlet valves. Pinacocytes , plate-like cells, form a single-layered external skin over all other parts of the mesohyl that are not covered by choanocytes, and the pinacocytes also digest food particles that are too large to enter

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