Invertebrates 6 Phylum Echinodermata

Phylum Echinodermata: Spiny-skinned

Evolutionary relationships and HOX genes

Echinodermata: 4 key features  Calcareous internal skeleton  Parts: Plates, spines and pedicellariae  Why considered “internal”?  Water vascular system (controls tube feet)  Derived from coelom  Layout  Tube foot control  Other functions  Symmetry  Bilateral symmetry (larvae)  Pentamerous radial symmetry (adults)  Mutable connective tissue

Body plan: Other aspects  Perivisceral coelom  Houses organs  Gas exchange  Hydrostatic skeleton  Digestive system  Can be highly branched  Complete (generally…)  Nervous system  No brain  Branches parallel water vascular system  Sensory (sea stars)  Eye spots  Receptors associated with tube feet  No circulatory system  No excretory system

Class Asteroidea: sea stars  Feeding  Respiration  Protection

Class Echinoidea: Sea urchins and others  Feeding  Respiration  Protection

Class Holothuroidea: Sea cucumbers

Class Ophioroidea: Brittle stars, basket stars  Feeding  Respiration  Protection

Class Crinoidea Sea lilies

Chordates! Subphylum Urochordata Subphylum Cephalochordata Subphylum Vertebrata (focus)

Evolutionary relationships and HOX genes

Phylum Chordata: 4 key features* *Each appears in a least one life stage

1) Notochord: Longitudinal flexible rod made of fluid-filled cells in fibrous tissue Dorsal Underlies nerve cord Replaced by jointed vertebral column in the vertebrates 2) Dorsal, Hollow Nerve Cord: Derived from ectoderm Develops into central nervous system (brain/spinal cord) 3) Pharyngeal Gill Slits: Slits in pharynx allowing for water efflux Multiple functions in vertebrates (e.g. feeding in tunicates, gills in fish) 4) Muscular, Post-anal Tail: Skeletal elements / muscle for mobility Phylum Chordata: 4 key features* *Each appears in a least one life stage

Subphylum Urochordata: the tunicates  Invertebrates (notochord but no vertebral column)  Larva has all five chordate features  Adults retain only the pharyngeal slits  Expanded pharynx works similarly to the ctenidium of a mussel…

Subphylum Cephalochordata: the lancelets  Invertebrates (notochord but no vertebral column)  Larva has all five chordate features  Adults retain all chordate features  Neoteny (paedogenesis) of a urochordate-like larva?  Muscles develop from somites: Blocks of mesoderm (segmented)  Feed similarly to the Urochordata