Unique features of sponges
Stony barrel sponge Xestospongia testudinaria, with a giant cavity at the top (cloacal cavity) containing exhalant breathing pores or oscules. Clathria (Microciona) mima, a common encrusting sponge on coral reefs throughout the Indo-Malay archipelago. Calcareous sponge Soleniscus radovani with an almost algae-like growth form, found commonly in coral reef caves on the Great Barrier Reef. Echinochalina isaaci, a unique species know so far only from the Great Barrier Reef. Highly flexible fan sponge, Ianthella basta, most common on the seabed and in high current areas. This burrowing sponge Aka sp. is highly specialised to excavating life style, with its exhalant breathing pores (oscula) on the ends of the open tubes (fistules), and the inhalant breathing pores (ostia) are clustered on the ends of the blind fistules to prevent smothering from the sediment.All sponges are aquatic, most are marine, found from the deepest oceans to sub-terrestrial environments (where they can survive remarkably well).
They are the most primitive of the multicellular animals. Their bodies lack true tissues but are composed of many different cell types each with special functions.
The sponge ‘skin’ is composed of special cells that surround the upper and lower surfaces of the body (exopinacocytes and basipinacocytes respectively), with a middle layer (or mesohyl) in which all the other cells occur.
Within this middle layer the body plan may vary from simple to complex, depending on the complexity of infolding of the body wall and water canals throughout the sponge. Most sponge body plans are complex and adults are asymmetrical (or some radially symmetrical).
Also within this middle layer, sponge cells roam throughout the body; transporting food, oxygen, waste products, building organic skeletons, secreting inorganic skeletons, or forming feeding chambers. This mobility of cells, together with their ability for cells to change function from a stem cell (archaeocyte) to any other cell type, and back again as needs be (totipotency), gives them a great evolutionary advantage. It means they can change growth forms depending on local environmental conditions. They are the ultimate plastic beings.
Sponges differ from other animal phyla by their unique possession of 5 distinct features.
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