Unformatted text preview: choanocytes, whose flagellar movements cause water to enter through the ostia and escape from the osculum. 3. How do sponges feed? Sponges are filter (or suspension) feeders. Choanocytes create a current of water. The flagellum of each choanocyte is surrounded by a collar-like sieve (composed of microvilli, cross-connecting microfibrils, and mucus) that functions as a filter. Water passes through this filter and small food particles (e.g., plankton) are trapped and ingested by the choanocyte and passed on to archaeocytes (ameboid cells) in the mesohyl for intracellular digestion. 4. What animal-like features are lacking in sponges? Sponges lack true tissues, a nervous system, muscle cells, differentiated head, etc. There is also no gastrulation and consequently no production of germ layers (ectoderm and entoderm). Nor is there an elaborate gas exchange and excretion system, since wastes and gases move by simple diffusion. 1...
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- Fall '09
- Spongin, Flagellated collar cells