Question

Compare and contrast the anatomical organization of sponges and cnidarians.   How do their differences shape their functional biology, especially feeding mode?

Answer 1

both of these organisms shows simple organization ,sponges have multiple cell types while cnidarians have outer and inner tissue layers sandwitching a noncellular mesoglea

sponges are marine usually much of bodystructure is dedicated to moving water through the body so it can filter out food , absorb dissolved oxygen and eliminate waste . the body is cylinder shaped with a large central cavity ,the spongocoel .water enters the spongocoel from numerous pores in the body wall . water flows out through a large opening called operculum . it has outer layer of flattened cells and innerlayer of choanocytes seperated by jelly like substance mesohyl. choanocytes embedded in mesophyl but flagellar part protruding in to spongocoel . beating of this flagella moves water through sponge food particles trapped in mucous produced by choanocytes and ingested by phagocytosis . this process is intracellular digestion . gas exchange ,circulation and excretion occur by diffusion between cells and water

cnidarians shows radial or biradial symmetry and are diploblastic , they are marine . they have stinging cells called cnidocytes concentrated around the mouth of organism .nematocyst of this stinging cells contain coiled threads . the outer wall of the cell has hairlike projection which is sensitive to touch . when touched the cells fire toxin contained threads that penetrate and immobilise the prey .

they have two distinct body forms polyp and medulla . polyps are sessile with mouth facing up surrounding with tentacles example -hydra. medulla are motile with hanging mouth and tentacles . cnidarians have two tissue layer .outer epidermis and inner gastrodermis , gastrodermis lines digestive cavity , between these 2 layers mesoglea like spongia . but the cells are differentiated here which is a major difference from spongia , nervecells , enzyme secreating cells ,nutrient absorbing cells are there . cnidarians perform extracellular digestion .it is another difference . but the digestion completed intracellularly

food is taken in to gastrovascular cavity , enzymes secreated and digestion take place , the nutrient absorbing cells lining the cavity absorb the products of extracellular digestion , gastrovascular cavity has single opening for ingestion and excreation , like spnges cells exchange gases and nitrogen waste by diffusion