Larval and Adult Characters in Animal Phytogeny

SYNOPSIS. Protostomes and deuterostomes can be characterizedby two completely separate sets of characters. Protostome charactersare downstream- collecting ciliary bands with compound ciliaon multiciliate cells and central nervous system with apicalbrain and ventral paired or fused cords; spiral cleavage isonly found in the protostome group Spiralia. Deuterostome charactersare upstream-collecting ciliary systems with separate ciliaon monociliate cells, dorsal central nervous system and lossof the larval apical organ in the adults, and archimery withprosome, mesosome and metasome. Only the ectoproct bryozoanslack all the justmentioned characters; they are referred tothe protostomes on basis of their metamorphosis which resemblesthat of entoprocts. The two bilateral groups have probably evolvedindependently from a radial, gastraea-like ancestor