Phylum Echinodermata

Ch.16

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

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.

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.

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

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!

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