Tagmata
head, thorax and abdomen
prosoma and an opisthosoma
cephalothorax and abdomen
multiplicity of segments
patterns of development
large yolky egg and embryo typically forms as a blastodisc, thus the protostomate origins are somewhat hidden.
the typical invertebrate is a marine aquatic, the arthropods have been the most successful group in inhabiting terrestrial ecosystems.

Phylum Mollusca
Characteristics
shell
mantle--the structure that secretes the shell
foot
paired gills
head and mouth in the mouth is radula
haemocoel
complete digestive tract
complex nervous systems

monoplacophora
polyplacophora
aplacophora
gastrodpoda
cephalopoda
bivalvia (pelecypoda)-lammelibranch
tooth or tusk shells (Dentalium--wampum)

Origin of mollusks
annelid

embryologic development--trochophore larvae turns into as development progresses in veliger larvae