What Type Of Animal Has Collar Cells, An Osculum, And Spicules?

28.1: Phylum Porifera

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Page ID

1968

Skills to Develop

• Describe the organizational features of the simplest multicellular organisms
• Explain the various body forms and bodily functions of sponges

The invertebrates, or invertebrata, are animals that do non contain bony structures, such as the cranium and vertebrae. The simplest of all the invertebrates are the Parazoans, which include only the phylum Porifera: the sponges (Figure \(\PageIndex{ane}\)). Parazoans ("beside animals") practise non display tissue-level organization, although they do have specialized cells that perform specific functions. Sponge larvae are able to swim; however, adults are not-motile and spend their life attached to a substratum. Since h2o is vital to sponges for excretion, feeding, and gas commutation, their body construction facilitates the movement of water through the sponge. Structures such as canals, chambers, and cavities enable water to move through the sponge to nearly all body cells.

Figure \(\PageIndex{1}\): Sponges are members of the Phylum Porifera, which contains the simplest invertebrates. (credit: Andrew Turner)

Morphology of Sponges

The morphology of the simplest sponges takes the shape of a cylinder with a big fundamental crenel, the spongocoel, occupying the inside of the cylinder. Water can enter into the spongocoel from numerous pores in the body wall. Water entering the spongocoel is extruded via a large common opening called the osculum. However, sponges exhibit a range of diversity in trunk forms, including variations in the size of the spongocoel, the number of osculi, and where the cells that filter food from the water are located.

While sponges (excluding the hexactinellids) do not exhibit tissue-layer organization, they do take different cell types that perform distinct functions. Pinacocytes, which are epithelial-like cells, class the outermost layer of sponges and enclose a jelly-like substance called mesohyl. Mesohyl is an extracellular matrix consisting of a collagen-like gel with suspended cells that perform various functions. The gel-like consistency of mesohyl acts similar an endoskeleton and maintains the tubular morphology of sponges. In add-on to the osculum, sponges have multiple pores called ostia on their bodies that allow water to enter the sponge. In some sponges, ostia are formed by porocytes, single tube-shaped cells that human activity as valves to regulate the menstruation of water into the spongocoel. In other sponges, ostia are formed by folds in the body wall of the sponge.

Choanocytes ("collar cells") are nowadays at diverse locations, depending on the blazon of sponge, but they always line the inner portions of some space through which h2o flows (the spongocoel in uncomplicated sponges, canals within the body wall in more complex sponges, and chambers scattered throughout the body in the most circuitous sponges). Whereas pinacocytes line the outside of the sponge, choanocytes tend to line sure inner portions of the sponge trunk that environs the mesohyl. The structure of a choanocyte is disquisitional to its function, which is to generate a h2o current through the sponge and to trap and ingest food particles by phagocytosis. Note the similarity in advent between the sponge choanocyte and choanoflagellates (Protista). This similarity suggests that sponges and choanoflagellates are closely related and probable share a contempo common ancestry. The cell body is embedded in mesohyl and contains all organelles required for normal prison cell function, but protruding into the "open up infinite" inside of the sponge is a mesh-like collar equanimous of microvilli with a single flagellum in the centre of the cavalcade. The cumulative effect of the flagella from all choanocytes aids the move of h2o through the sponge: drawing water into the sponge through the numerous ostia, into the spaces lined past choanocytes, and eventually out through the osculum (or osculi). In the meantime, food particles, including waterborne bacteria and algae, are trapped by the sieve-like collar of the choanocytes, slide down into the torso of the cell, are ingested past phagocytosis, and become encased in a nutrient vacuole. Lastly, choanocytes will differentiate into sperm for sexual reproduction, where they volition become dislodged from the mesohyl and leave the sponge with expelled water through the osculum.

The second crucial cells in sponges are called amoebocytes (or archaeocytes), named for the fact that they motion throughout the mesohyl in an amoeba-like fashion. Amoebocytes have a variety of functions: delivering nutrients from choanocytes to other cells within the sponge, giving rise to eggs for sexual reproduction (which remain in the mesohyl), delivering phagocytized sperm from choanocytes to eggs, and differentiating into more-specific jail cell types. Some of these more than-specific jail cell types include collencytes and lophocytes, which produce the collagen-like protein to maintain the mesohyl, sclerocytes, which produce spicules in some sponges, and spongocytes, which produce the protein spongin in the majority of sponges. These cells produce collagen to maintain the consistency of the mesohyl. The different prison cell types in sponges are shown in Figure \(\PageIndex{2}\).

Figure \(\PageIndex{2}\): The sponge'due south (a) basic trunk programme and (b) some of the specialized jail cell types constitute in sponges are shown.

Exercise \(\PageIndex{1}\)

Which of the following statements is false?

1. Choanocytes accept flagella that propel h2o through the body.
2. Pinacocytes can transform into whatsoever cell type.
3. Lophocytes secrete collagen.
4. Porocytes control the flow of water through pores in the sponge torso.

Answer

B

In some sponges, sclerocytes secrete small spicules into the mesohyl, which are equanimous of either calcium carbonate or silica, depending on the type of sponge. These spicules serve to provide additional stiffness to the body of the sponge. Additionally, spicules, when present externally, may ward off predators. Another type of protein, spongin, may too be present in the mesohyl of some sponges.

The presence and limerick of spicules/spongin are the differentiating characteristics of the three classes of sponges (Figure \(\PageIndex{three}\)): Class Calcarea contains calcium carbonate spicules and no spongin, form Hexactinellida contains half dozen-rayed siliceous spicules and no spongin, and grade Demospongia contains spongin and may or may not have spicules; if present, those spicules are siliceous. Spicules are most conspicuously present in class Hexactinellida, the guild consisting of glass sponges. Some of the spicules may achieve behemothic proportions (in relation to the typical size range of glass sponges of 3 to 10 mm) as seen in Monorhaphis chuni, which grows up to 3 one thousand long.

Figure \(\PageIndex{3}\): (a) Clathrina clathrus belongs to course Calcarea, (b) Staurocalyptus spp. (mutual proper name: yellow Picasso sponge) belongs to course Hexactinellida, and (c) Acarnus erithacus belongs to class Demospongia. (credit a: modification of work by Parent Géry; credit b: modification of work by Monterey Bay Aquarium Research Institute, NOAA; credit c: modification of work past Sanctuary Integrated Monitoring Network, Monterey Bay National Marine Sanctuary, NOAA)

Physiological Processes in Sponges

Sponges, despite being unproblematic organisms, regulate their different physiological processes through a variety of mechanisms. These processes regulate their metabolism, reproduction, and locomotion.

Digestion

Sponges lack complex digestive, respiratory, circulatory, reproductive, and nervous systems. Their food is trapped when h2o passes through the ostia and out through the osculum. Leaner smaller than 0.5 microns in size are trapped by choanocytes, which are the main cells engaged in nutrition, and are ingested by phagocytosis. Particles that are larger than the ostia may be phagocytized by pinacocytes. In some sponges, amoebocytes ship food from cells that have ingested food particles to those that do not. For this type of digestion, in which food particles are digested within private cells, the sponge draws water through improvidence. The limit of this type of digestion is that nutrient particles must be smaller than individual cells.

All other major trunk functions in the sponge (gas exchange, circulation, excretion) are performed past diffusion betwixt the cells that line the openings inside the sponge and the h2o that is passing through those openings. All cell types inside the sponge obtain oxygen from water through diffusion. Too, carbon dioxide is released into seawater by diffusion. In addition, nitrogenous waste matter produced equally a byproduct of protein metabolism is excreted via improvidence by individual cells into the water equally it passes through the sponge.

Reproduction

Sponges reproduce by sexual every bit well as asexual methods. The typical means of asexual reproduction is either fragmentation (where a piece of the sponge breaks off, settles on a new substrate, and develops into a new individual) or budding (a genetically identical outgrowth grows from the parent and eventually detaches or remains attached to form a colony). An singular blazon of asexual reproduction is found just in freshwater sponges and occurs through the formation of gemmules. Gemmules are environmentally resistant structures produced by adult sponges wherein the typical sponge morphology is inverted. In gemmules, an inner layer of amoebocytes is surrounded past a layer of collagen (spongin) that may be reinforced by spicules. The collagen that is unremarkably found in the mesohyl becomes the outer protective layer. In freshwater sponges, gemmules may survive hostile environmental conditions like changes in temperature and serve to recolonize the habitat in one case environmental weather stabilize. Gemmules are capable of attaching to a substratum and generating a new sponge. Since gemmules can withstand harsh environments, are resistant to desiccation, and remain dormant for long periods, they are an excellent ways of colonization for a sessile organism.

Sexual reproduction in sponges occurs when gametes are generated. Sponges are monoecious (hermaphroditic), which ways that 1 individual can produce both gametes (eggs and sperm) simultaneously. In some sponges, production of gametes may occur throughout the yr, whereas other sponges may show sexual cycles depending upon water temperature. Sponges may likewise become sequentially hermaphroditic, producing oocytes first and spermatozoa later. Oocytes ascend by the differentiation of amoebocytes and are retained within the spongocoel, whereas spermatozoa event from the differentiation of choanocytes and are ejected via the osculum. Ejection of spermatozoa may be a timed and coordinated event, every bit seen in certain species. Spermatozoa carried along by water currents can fertilize the oocytes borne in the mesohyl of other sponges. Early larval development occurs within the sponge, and gratuitous-swimming larvae are then released via the osculum.

Locomotion

Sponges are mostly sessile as adults and spend their lives attached to a fixed substratum. They do non show movement over big distances like other free-pond marine invertebrates. Still, sponge cells are capable of creeping along substrata via organizational plasticity. Under experimental conditions, researchers have shown that sponge cells spread on a physical support demonstrate a leading edge for directed movement. It has been speculated that this localized creeping motility may help sponges adjust to microenvironments near the point of attachment. Information technology must be noted, however, that this pattern of movement has been documented in laboratories, but it remains to exist observed in natural sponge habitats.

Summary

Animals included in phylum Porifera are Parazoans because they practice not evidence the formation of truthful tissues (except in grade Hexactinellida). These organisms evidence very simple organization, with a rudimentary endoskeleton. Sponges have multiple cell types that are geared toward executing various metabolic functions. Although these animals are very simple, they perform several complex physiological functions.

Glossary

amoebocyte

sponge cell with multiple functions, including nutrient delivery, egg formation, sperm delivery, and cell differentiation

choanocyte

(likewise, collar cell) sponge cell that functions to generate a water current and to trap and ingest food particles via phagocytosis

gemmule

construction produced past asexual reproduction in freshwater sponges where the morphology is inverted

invertebrata

(also, invertebrates) category of animals that do non possess a cranium or vertebral cavalcade

mesohyl

collagen-like gel containing suspended cells that perform various functions in the sponge

osculum

large opening in the sponge's body through which h2o leaves

ostium

pore present on the sponge's body through which water enters

pinacocyte

epithelial-like cell that forms the outermost layer of sponges and encloses a jelly-like substance chosen mesohyl

Porifera

phylum of animals with no true tissues, just a porous trunk with rudimentary endoskeleton

sclerocyte

prison cell that secretes silica spicules into the mesohyl

spicule

structure made of silica or calcium carbonate that provides structural support for sponges

spongocoel

central cavity within the body of some sponges

Source: https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/Book%3A_General_Biology_(OpenStax)/5%3A_Biological_Diversity/28%3A_Invertebrates/28.1%3A_Phylum_Porifera

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