Echinodermata

A phylogeny can help us do lots more than simply study evolutionary history. It also helps us know what traits are shared by different but related groups of organisms.

1: Multicellular2: Land plants3: Vascular plants4: Seed plants5: Symmetry and tissues6: Bilateral symmetry, coelom, and nervous system7: Deuterostome development8: Molting of exoskeletons9: Trochophore larva

Adults exhibit pentaradial symmetry, but the larvae are bilaterally symmetrical

Echinoderms are considered deuterostomes, anus formed first

Lack cephalization, have few sensory organsHave 2 sides: oral-the side with the mouth, aboral-the

side without the mouth

The water vascular system aids in locomotion, feeding, attachment, respiration

Water enters through the madreporite and moves through the organism to the arms and tube feet

Tube feet fill with water and help the organism grab surfaces and pull themselves along

Some species have regenerative tissue, they can re-grow limbs

Class: CrinoideaSea lilies and feather stars

This class attaches to a substrate with a stalk

Appx 700 extant species

Class: AsteroideaSea starsArms radiate from a central disc, but are not distinct from

itMadreporite and anus are on aboral sideMove with tube feet

Class: OphiuroideaBrittle StarsTheir flexible arms branch from a small central discMadreporite is on oral sideMouth and anus are the same openingThe aboral surface of the disc is protected by plates

called sheilds

Class: EchinoideaSea urchins and sand dollars and sea biscuitsMost are free moving but some bore into rockTube feet bring food into their mouthsTheir teeth are arranged into a structure

known as Aristotle’s Lantern

Class: HolothuroideaSea cucumbersWhen threatened, they can expel their

intestines, which are regenerated later