Trends in Animal Evolution Acoelomate Pseudocoelomate Body cavity endoderm mesoderm ectoderm Coelomate

Trends in Coelomate Evolution Cleavage Deuterostomes  Radial Cleavage Protostomes  Spiral Cleavage

Trends in Coelomate Evolution Coelom Formation Cells migrate from existing cell layers, forming a solid tissue layer which splits; mouth forms from opening Mesoderm forms from outpockets of endoderm; anus forms from opening Protostomes Deuterostomes Gastrula stage ectoderm endoderm coelom

The Coelomates Internal body cavities Skeletons (internal and external) m.y.b.p m.y.b.p. 66 m.y.b.p. - present Coeloms & external skeletons

The Coelomates Advantages of External Shells/Skeletons Secretion of mineral shell (stores minerals) Protection from desiccation Protection from predators Muscle attachment (locomotion & strength)

Phylum Mollusca

Class Polyplacophora Class CaudofoveataClass Solenogastres Class Monoplacophora Class Scaphopoda Class Gastropoda Class Bivalvia Class Cephalopoda Subphylum Conchifera

protostomates mantle head foot Key Characteristics coelomates mosaic/determinant development

Cephalization head is well developed, with one or two pairs of antennae and, in some species, eyes Key Characteristics

radula

Key Characteristics Trocophore and Veliger Larvae

Class Caudofoveata Class Solenogastres (nee Class Aplacophora)

Class Polyplacophora The Chitons 8 shell plates mantle “girdle”

Class Monoplacophora

Class Scaphopoda

Class Gastropoda marine, freshwater, terrestrial well developed head with eyes and tentacles torsion

RESPIRATORY SYSTEM Gills Diffusion across skin “Lung”

TORSION BEFORE AFTER dorsal viewside view

FOULING PROBLEMS ASSOCIATED WITH TORSION

Class Bivalvia second largest class of molluscs mainly marine, with a few freshwater species no head, no radula, reduced cephalization

Locomotion hydraulics

Bivalve Gills used in feeding and oxygen uptake

Class Cephalopoda nautiloids squids octopus cuttlefish

Key Characteristics mantle surrounds viscera and forms siphon ink gland beak-like jaws large, circumoral tentacles/arms formed from foot image forming eyes & large brain shell present in all except octopods

Rotation of Body Axis

Nautiloid Shell shell is divided by a series of internal septa septa are perforated by body extension (the siphuncle) the siphuncle regulates buoyancy of the chambers septum siphuncle

Cephalopod Locomotion jet propulsion water is forced out of the mantle cavity through a siphon

Camouflage

mass of squid egg capsules close-up of egg capsules eggs in early stages of development

fertilized eggs late development- stage egg freshly hatched squidlet Direct development of the squid