BISC 306 Chapter Notes -Strobilation, Rhopalium, Mesoglea
19 Nov 2012
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Rigid, perforated bag lined with flagellated collar cells or choanocytes (inside): generate currents to maintain circulation, capture small food particles, capture sperm. Empty space in the middle is called the spongocoel. Between inner choanocyte layer and outer pinacocyte (epidermis) layer is the mesohyl: gelatinous, acellular, contains free floating archaeocytes (amoeboid) Digest food, give rise to sperm/eggs, defense, eliminating wastes and specialization for secretion of spicules. Spicules are siliceous or calcareous: discourage predation. Gemmules are dormant structures from which a sponge emerges: resistant to dessication, etc, alternative to tissue regression. Pinacocytes form the pinacoderm (outer layer: do not secrete a basal lamina, contractile. Syconoids are more complex, with pockets of choanocytes. Pockets and pockets of choanocytes increase surface area, and instead of one osculum, they have many oscula. Secrete poisons that range from large organic molecules or small ones: have anticancer, etc, properties. Supported entirely by interconnected six-rayed spicules of silica and chitin.
