BIO2231 Chapter Notes -Gastrovascular Cavity, Pedal Disc, Precious Coral
Document Summary
Most are sessile feeders; those that are attached, such as jellyfish, swim only feebly. They are very effective predators that are able to kill and eat prey. They possess tentacles that bristle with tiny, sophisticated weapons called nematocysts. Like a cocked- gun, a completed nematocyst requires only a small stimulus to make it fire. It instantly penetrates its prey and injects a paralyzing toxin. Cnidarians are diploblastic, meaning that they have 2 embryonic cell layers, ectoderm and endoderm, form which adult structures develop. Two layers are produced as the embryo develops from a single-layers blastula to a gastrula. In adult diploblasts, the epidermis develops from ectoderm, and the gut cavity lining/gastrodermis develops from endoderm; this body plan is in marked contrast to that of adult sponges, where there are neither cell layers nor a gut cavity. A new stage of development, gastrulation, characterizes diploblasts and produced the cell layers of adult animals. They exhibit radial/biradial symmetry and are not cephalised.
