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30. Echinodermata Introduction to Spiny-skinned Sea Animals Apparent Radial Symmetry compare Hickman Fig. 23-3 like spokes of a wheel sea star Secondary Radial Symmetry anterior •ancestors were bilateral food – larvae are initially bilateral ventral – but radial after metamorphosis •oral-aboral axis – not original anterior-posterior – but from embryo’s left-right dorsal posterior bipinnaria larva of starfish, left side Compare Hickman Fig. 23-9 axis Starfish Metamorphosis Compare Hickman Fig. 23-9 brachiolaria bipinnaria aboral attachment stalk is lost later developing arms of adult oral Echinoderm Habitat • entirely marine • larvae are planktonic and Bilateral • adults are entirely benthic – radial body plan is best for sessile life style • radial symmetry of echinoderms is evidence that their ancestors were sessile – but most adults can crawl, and tend back toward bilateral symmetry Water Vascular System • unique to echinoderms • used for locomotion and food-gathering Components: • madreporite for water exchange • hydraulic tubing: – stone canal, ring canal, radial canals • tube feet with internal ampullae Starfish Anatomy Fig 23-3 pyloric stomach cardiac stomach bony internal skeleton elements of water vascular system Tube Feet of Sea Star (similar in sea urchins and sea cucumbers) equipped with: internal ampulla, valves, and many tiny muscles connector to a radial canal Sea Stars Are Carnivores Fig. 23-5 Skeleton and Skin compare Hickman Fig. 23-4 • bony endoskeleton and spines • pedicellariae – tiny pincers on stalks – for defense and feeding • many, tiny gills gill pedicellaria bony spine bony ossicle zoologist’s forceps sea star’s tube feet barnacle larva Sea Urchin Pedicellariae (also in sea stars) compare Hickman Fig. 23-4 Reproduction • mostly sexual, adults diecious • sea stars can regenerate severed arms • some kinds can break apart and re-grow into two sea star, regenerating arms Hickman Fig. 23-8 Echinoderm Classes Variations on Echinoderm Body design Classification about 6,000 species • • • • • Asteroidea - sea stars, or starfish Echinoidea - sea and heart urchins, sand dollars Ophiuroidea - brittle, serpent, and basket stars Crinoidea - sea lilies, feather stars Holothuroidea - sea cucumbers Asteroidea - Sea Stars or Starfish Fig. 23-1 Echinoidea compare 23-16,17,18,19 sea urchin some have poisonous spines sand dollar Sea Urchin Anatomy Hickman Fig. 23-19 Aristotle’s lantern (five jaws, for scraping algae) Ophiuroidea - Brittle or Serpent Stars compare 23-14 Scavengers and passive suspension-feeders Brittle Star Anatomy Hickman Fig. 23-12,13 ventral view of disk lateral, cut-away view of disk madreporite on oral side blind gut Crinoidea - Feather Stars or Sea Lilies Hickman Fig. 23-25 passive filter-feeders Model of Paleozoic, Crinoid “Garden” Feather Star Anatomy pinnules (tube feet that catch food particles) arms mouth cilia cause mucus flow pinnules Holothuroidea- Sea Cucumbers compare 23-23,24 tentacles tube feet deposit-feeder suspension-feeder Sea Cucumber Anatomy Hickman Fig. 23-23 oral (“anterior”) dissected tube feet aboral (“posterior”) radial canals intestine
