Echinoderms and Chordate Characteristics

Echinoderms

• benthic, marine

• rich fossil record

• deutersostomes

• radial symmetry (mostly pentaradial)

• Grazers, filter, suspension, and deposit feeders

• Have bilateral symmetry as larvae, so radial symmetry evolved independently

• Dermal skeleton made of CaCO3 (ossicles)

• Catch collagen is a mutable collagen used to connect ossicles (hold position) with little energy

• Dermal branchiae (papulae) are used for respiratory gas exchange (“skin gills”)

• Pedicellarieae are mostly used for protection; prevent crusting on body; can also collect small amounts of food

Ambulacra

“alleyway”; row with tube feet

Class Asteroidea

“sea stars”; five arms that gradually merge into central disc; mostly feed on bivalves

Class Ophiuroidea

snake, brittle, basket stars; long, skinny arms

Class Echinodea

sea urchins, sand dollars; no distinct arms, have spines instead; movement by tube feet and spines; flat/globular; scavengers and grazers; herbivorous; use “Aristotle’s Lantern”; sand dollars and heart urchins specifically have short spines, flattened oral-aboral axis, and secondary bilateral symmetry

Class Holothuroidea

sea cucumbers; some secondary bilateral symmetry; oral tentacles catch food; mostly deposit or suspension feeders; “lick their fingers”; cuvierian tubules (part of respiratory tree) can be expelled for defense, are sticky, toxic, and entangling, and cannot retract, but can grow back

Class Crinoidea

crinoids, sea lilies, feather stars; long, stalk-like arms; abundant fossils; deep sea

Chordate Characteristics

• Notochord

• Dorsal, hollow nerve cord

• Pharyngeal pouches or slits

• Endostyle or thyroid gland

• Postanal tail