In some sponges, sclerocytes secrete small spicules into the mesohyl, which are composed of either calcium carbonate or silica, depending on the type of sponge. The cumulative effect of the flagella from all choanocytes aids the movement of water through the sponge: drawing water into the sponge through the numerous ostia, into the spaces lined by choanocytes, and eventually out through the osculum (or osculi). In some sponges, production of gametes may occur throughout the year, whereas other sponges may show sexual cycles depending upon water temperature. sponge's "skeleton" Term. The different cell types in sponges are shown in [Figure 2]. The difference between this and the mechanisms of other animals is that digestion takes place within cells rather than outside of cells. 10/12/2005. Choanocytes (“collar cells”) are present at various locations, depending on the type of sponge, but they always line the inner portions of some space through which water flows (the spongocoel in simple sponges, canals within the body wall in more complex sponges, and chambers scattered throughout the body in the most complex sponges). 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 cell types. Sponges are only just classed as animals. Sponges, despite being simple organisms, regulate their different physiological processes through a variety of mechanisms. Porocytes control the flow of water through pores in the sponge body. Sponges may also become sequentially hermaphroditic, producing oocytes first and spermatozoa later. We definitely need to insert humor into biology. These organisms show very simple organization, with a rudimentary endoskeleton. In some sponges, sclerocytes secrete small spicules into the mesohyl, which are composed of either calcium carbonate or silica, depending on the type of sponge. Choanocytes (“collar cells”) are present at various locations, depending on the type of sponge, but they always line the inner portions of some space through which water flows (the spongocoel in simple sponges, canals within the body wall in more complex sponges, and chambers scattered throughout the body in the most complex sponges). Sponges are generally sessile as adults and spend their lives attached to a fixed substratum. The simplest of all the invertebrates are the Parazoans, which include only the phylum Porifera: the sponges ([Figure 1]). The sponges draw water carrying food particles into the spongocoel using the beating of flagella on the choanocytes. Choanocytes have flagella that propel water through the body. In the meantime, food particles, including waterborne bacteria and algae, are trapped by the sieve-like collar of the choanocytes, slide down into the body of the cell, are ingested by phagocytosis, and become encased in a food vacuole. In other sponges, ostia are formed by folds in the body wall of the sponge. The structure of a choanocyte is critical to its function, which is to generate a water current through the sponge and to trap and ingest food particles by phagocytosis. Oocytes arise by the differentiation of amoebocytes and are retained within the spongocoel, whereas spermatozoa result from the differentiation of choanocytes and are ejected via the osculum. Did you have an idea for improving this content? Created. While sponges (excluding the hexactinellids) do not exhibit tissue-layer organization, they do have different cell types that perform distinct functions. Porocytes control the flow of water through pores in the sponge body. (common name: yellow Picasso sponge) belongs to class Hexactinellida, and (c) Acarnus erithacus belongs to class Demospongia. ... What is a spongin? The presence and composition of spicules/spongin are the differentiating characteristics of the three classes of sponges (shown in Figure 3): Class Calcarea contains calcium carbonate spicules and no spongin, class Hexactinellida contains six-rayed siliceous spicules and no spongin, and class Demospongia contains spongin and may or may not have spicules; if present, those spicules are siliceous. In some sponges, ostia are formed by porocytes, single tube-shaped cells that act as valves to regulate the flow of water into the spongocoel. Since gemmules can withstand harsh environments, are resistant to desiccation, and remain dormant for long periods, they are an excellent means of colonization for a sessile organism.
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