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Trends in Animal Evolution. Body cavity. Coelomate. Pseudocoelomate. Acoelomate. endoderm mesoderm ectoderm. Trends in Coelomate Evolution. Deuterostomes Radial Cleavage. Protostomes Spiral Cleavage. Cleavage. Trends in Coelomate Evolution. coelom. Coelom Formation.
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Trends in Animal Evolution Body cavity Coelomate Pseudocoelomate Acoelomate endodermmesodermectoderm
Trends in Coelomate Evolution Deuterostomes RadialCleavage Protostomes SpiralCleavage Cleavage
Trends in Coelomate Evolution coelom Coelom Formation Deuterostomes Mesoderm forms from outpockets of endoderm; anus forms from opening Gastrula stage ectoderm endoderm Cells migrate from existing cell layers, forming a solid tissue layer which splits; mouth forms from opening Protostomes
66 - 245 m.y.b.p. The Coelomates Internal body cavities Skeletons (internal and external) 66 m.y.b.p. - present 245 - 540 m.y.b.p. Coeloms & external skeletons The Cambrian Explosion!
The Coelomates Advantages of External Shells/Skeletons Secretion of mineral shell (stores minerals) Protection from desiccation Protection from predators Muscle attachment (locomotion & strength)
Class Caudofoveata Class Solenogastres Subphylum Aculifera Class Polyplacophora Subphylum Conchifera Class Monoplacophora Class Scaphopoda Class Gastropoda Class Bivalvia Class Cephalopoda
coelomates Key Characteristics protostomates mosaic/determinant development mantle head foot
Key Characteristics 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 Gastropoda • marine, freshwater, terrestrial • well developed head with eyes and tentacles • torsion
RESPIRATORY SYSTEM Gills Diffusion across skin “Lung”
TORSION BEFORE AFTER dorsal view side view
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
Glochidia Dispersal stage unique to freshwater mussels video
Class Cephalopoda squids cuttlefish octopus nautiloids
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
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 siphuncle septum
Cephalopod Locomotion jet propulsion water is forced out of the mantle cavity through a siphon
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