BIOL 206 Chapter Notes - Chapter 31: Peritoneum, Body Cavity, Cephalization
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External appendages that are used for sensing, chewing, locomotion, mating and other functions. The development of the nervous system: overall shape of an animal can be described by its symmetry. And animal is symmetrical if it can be divided along at least one plane into similar halves. Animals with no planes of symmetry= asymmetrical. Ex: sponges: spherical symmetry- simplest form of symmetry body points radiate out from a central point. An infinite number of planes passing through the central point can divide a spherical symmetrically organism into similar halves. Bod(cid:455) parts are arra(cid:374)ged arou(cid:374)d o(cid:374)e (cid:373)ai(cid:374) a(cid:454)is at the (cid:271)od(cid:455)"s (cid:272)e(cid:374)ter. A perfectly symmetrical animal can be divided into similar halves by an plane that contains the main axis. But most radially symmetrical animals including sea stars are slightly modified so that only some planes can divide them into identical halves. Others can move slowly: bilateral symmetry characteristic of animals that have a distinct front end.
