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33_Ward_Echinodermata+Outline - Sea stars(Asteroidea •...

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BIS2C W2011 Lecture 33 (7 March 2011) 1 Echinodermata Introduction to Deuterostomes Bilateria with (1) radial cleavage, (2) anus arising from blastopore, (3) mesoderm and coelom deriving from outpocketing of gut wall (enterocoely). Two major clades: (Echinoderms + Hemichordates) and Chordates Echinodermata sea lilies, sea stars, brittle stars, sea urchins, sea cucumbers marine organisms, with variable feeding habits (predators, grazers, particle feeders) 7,000 extant species; 13,000 fossil species Features of Echinodermata calcareous endoskeleton pentaradial symmetry complex water vascular system complete gut diffuse nervous system (no brain) respiration and excretion by diffusion Sexual reproduction: mostly dioecious, with external fertilization Regeneration of body parts and asexual reproduction also common. Five major groups: Sea lilies, feather stars (Crinoidea) flower-shaped body; oral surface facing up sea lilies attached to stalk; feather stars more mobile
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Unformatted text preview: Sea stars (Asteroidea) • central disk, with large arms • common, many are predatory Crown-of-thorns starfish effects on coral reefs. Brittle stars (Ophiuroidea) • long slender arms that provide locomotion • abundant but secretive (light-avoiding) BIS2C W2011 Lecture 33 (7 March 2011) 2 Sea urchins (Echinoidea) • no arms; usually with long spines • ossicles fit together into a test • omnivores; important as grazers of algae Examples of “keystone species”: 1. Diadema sea urchins in the Caribbean 2. Kelp-consuming sea urchins off the California coast Sea cucumbers (Holothuroidea) • soft-bodied and slug-like • elongated oral/aboral axis, secondary bilateral symmetry • can expel parts of their gut as anti-predator defense (see: http://www.youtube.com/watch?v=lKWSLg5PDiU ) Web sites http://tolweb.org/tree?group=Echinodermata&contgroup=Deuterostomia http://research.calacademy.org/research/izg/echinoderm/ http://en.wikipedia.org/wiki/Echinoderms...
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