Phylum Echinodermata

1. Phylum Echinodermata Ch.16

2. Phylum Echinodermata • ~7,ooo Species • Triploblastic, coelomate, ALL marine • Pentaradial symmetry • (Body parts arranged in fives or a multiple of five) • Complete Digestive Tract • Regeneration • Most are dioecious, some are moneocious • Most use external fertilization • Water-vascular system (Figure 16.4) • Madreporite  Stone canal  Ring canal  5 radial canals branch off  Lateral canals  Tube feet

3. Class Asteroidea • Sea stars, about 1,500 species • May be brightly colored with red, orange, or blue • Most have 5 arms that radiate from central disc • Oral surface down and in middle • Dermal branchiae in skin (gas exchange) • Water-vascular system • Suction disks of tube feet are used for attachment and movement • Sea stars feed on snails, bivalves, crustaceans, corals, and a variety of other food items • Are well known for regeneration, they can regenerate any part of a broken arm….an entire sea star can be regenerated from a broken arm IF the arm contains a portion of the central disk…it is a slow process, taking up to a year for complete regeneration.

4. Class Ophiuroidea • Greek for snake (orphis) tail (oura) in the form of (oeides) • Brittle stars & Basket stars, over 2,000 species • Most diverse group of Echinoderms • Are predators and scavengers • The mouth leads to a sac-like stomach, and no part of the digestive tract extends into the arms • Water-vascular system used for capturing prey, not for locomotion • Tube feet lack suction cups, successive ossicles articulate and are acted upon by large muscles to produce snake like movement (hence the name of the class) • Like sea stars, ophiuroids can regenerate lost arms. If a brittle star is grasped by an arm, the brittle star will cast off the arm, this process called autonomy (Greek: autos=self + tomos=to cut) is used in escape reactions! • Dioecious, and males are generally smaller than females.

6. Class Echinoidea • Sea urchins, sand dollars, about 1,000 species • Sea urchins live on hard substrates, sand dollars live in sand or mud • Feed on dead animal remains, plankton, algae • Aristotle’s lantern – 35 teeth-like ossicles (a chewing apparatus) used in feeding • Urchins – hard surfaces, move by spines and tube feet, some have venom • Sand Dollars – burrow just below surface

7. Class Holothuroidea • Sea cucumbers, about 1,500 species • Found at all depths of the ocean, and crawl or burrow • Have no arms, and they are elongated along the oral-aboral axis and have enlarged tube feet around mouth. • Are ~10-30 cm in length • Ingest organic matter, use tentacles • Edible – “trepang” in Asia (body wall boiled and dried) • Water-vascular system internal & has coelomic fluid • Mostly sea cucumbers are defenseless against prey…but…. • Many produce toxins that discourage predators • Some eject sticky internal tubules that contain toxins (from the anus) to confuse predators • Some cause internal structures to explode (basically blowing up their body) in response to chemical and physical stress as a defensive adaptation to discourage predators, regeneration of lost parts follows!

9. Class Crinoidea • Feather stars, sea lilies, about 230 species • Most primitive of all echinoderms • Many species in fossil record • Attach permanently to a substrate and filter water for plankton • Sea lilies attached by a stalk • Feather stars have no stalk • Feather stars swim by raising and lowering arms