evolution

aerate

gizzard

phylogenetic tree

body plan

asymmetrical

sessile

radial symmetry

longitudinal

bilateral symmetry

motile

anterior

posterior

marine

cephalisation

Germinal layer

mesoderm

specialised

diploblastic

mesoglea

triploblastic

coelom

acoelomate

coelomate

haemocoel

osculum

paralysed

dorsoventrally

hydrostatic skeleton

appendages

notochord

protostomes

deuterostomes

diversity