Phylum Annelida

Abstract

All the remaining members of the animal kingdom possess, at least at some stage in their development, a coelom, and therefore are referred to as coelomates. There are five major coelomate phyla: Annelida, Arthropoda, Mollusca, Echinodermata and Chordata, with many minor phyla. Apart from their possession of a coelom, all these animals show greater complexity than pseudocoelomate and acoelomate forms. For instance, a through gut and a circulatory system are found in forms such as the nemerteans; however such systems are far more complex in the coelomates, elaboration being due to a large extent to their possession of a coelom. Coelomates also show increasing complexity within their nervous system associated with more elaborate behaviour patterns.