04 October

Tagmata--differ amongst the groups of arthropods

• 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

Molluscan taxonomy

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

Origin of mollusks

related very closely to the annelids

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