BIO325H5 Lecture Notes - Lecture 14: Particulates, Parapodium, Tube Feet

46 views3 pages
18 Apr 2016
School
Department
Course
Professor

Document Summary

Phylum echinodermata, class crinoidea, order comatulida (stalkless crinoid) Pentamerous crown attached to stalk on aboral side. Some primitive species of commatulid have 5 arms but in most species each arm forks as it leaves the calyx so the number of arms winds up as 10. In some species further branching can create up to 200 arms. Arms are the basis of a huge filter used to obtain particulate food. Note whorls of jointed cirri in the sea lily drawing. Feeding process involves structures called here for convenience podia", though in commatulids we see their original function. Three types can be recognized: primary, secondary and tertiary. The tube feet of modern starfish, sea urchins, sand dollars began their evolution as devices for intercepting particulate food items. From ancestors that moved with their mouth pointed upward they came to move with their mouths pointed downward. The fans fit are moved in a to-fro cycle, making a power then a recovery stroke.