BI256 Lecture Notes - Lecture 18: Veliger, Conchiolin, Periostracum
Document Summary
If present, secreted by the mantle and lined by it. Composed of conchiolin, a tanned protein (=formation of crosslinking between proteins) Next to the mantle; the nacre is laid down in thin layers. Open - pumping heart, blood vessels, and blood sinuses. Closed - most cephalopods have a heart, vessels, and capillaries. Most molluscs have a pair of kidneys or metanephridia. Kidney ducts also discharge sperm and eggs. Pairs of ganglia but generally simpler than in annelids. Sense organs vary and may be highly specialized. Copulation occurs and gametes exchanged in genetical ducts. Games released to surround water results in the development of free-swimming larval stages. May feed, catching small plankton in prototroch, planktotropic. Non-feeding trochophores have large yolk reserves, lecithotrophic have short planktonic lives. May exhibit direct metamorphosis into small juvenile (ex: polyplacophorans = chitons) In bivalves, most often developed into a second, free-swimming, larval stage. Veliger is symmetrical and enclosed within two valves (shell)
