KINGDOM ANIMALIAPhylum Echinodermata

Members of the Phylum Echinodermata

Date back 570 million years ago

13,000 fossil species

Only 7,000 species today

Most are marine and benthic (90%)

Range in size (<1cm to 2 m)

5 Classes

Common Body Plan

Adults are pentaradially symmetrical

5 sets of body parts around an oral-aboral axis

Common Body PlanHowever, larvae are bilaterally symmetricalSettle near adults of their species and attach to

substrateMetamorphosis: left side becomes oral surface of

the adult and right side becomes aboralLarval mouth/anus disappear, gut migrates to adult

position, and new mouth/anus open

Endoskeleton

Unique system of calcareous plates (ossicles)

Reduced in sea cucumbersFused to form a solid test in

sea urchins/sand dollars

Endoskeleton

Skeletal elements bear pincer-like structures called pedicellariae

Use to rid body of debris, defense, grasp objects to hide, or capture/hold prey

Water-vascular system

Hydraulic system of canals and reservoirs controls the movement of tube feet (podia)

Critical to locomotion, gas exchange, feeding, and sensory reception

Water-vascular systemWater enters sieve

plate (madreporite)Flows from stone

canal to radial canals in each arm

Lateral canals perpendicular to the radial canal terminate in muscular bulb (ampulla) connected to a tube foot

Water-vascular systemWater enters bulb, it

contracts and water forced into foot

Extends foot, pressing terminal sucker onto substrate

Foot contracts, forcing water back into bulb and raises center of sucker

Creates a vacuum seal; only broken when bulb contracts water into foot again

Classification

There are 6 classes of echinoderms

5 classes are described on the following slides

Class Crinoidea

Most ancient/primitive625 speciesBase of 5 or 10 arms that can branch

up to 200 armsSuspension feedersEach arm bears suckerless podia

that produce mucus to capture detritus and transport it to mouth

Class Crinoidea

Sessile sea lilyCup-like body

attached to stalkAttached to

substrateCan bend stalk

and flex/extend arms

Class Crinoidea

Free-moving feather star

Stalk lost during larval development

Can crawl/swimJointed

appendages (cirri) help it regain balance

Class Asteroidea1500 species of sea

stars5 or more broad arms

surround a central diskCrawl on rocks or live

on sea bottomMost are scavengers

or predatorsEach arm bears podia

with suckersEvert stomach into

prey and digest it

Class Ophiuroidea

2000 species of brittle stars

Usually concealed in sand or under objects

Some live in sponges or other colonial organisms

Only 5 arms that are usually highly branched

Arms are distinct from central disk

Can crawl/clingPredators,

scavengers, or suspension feeders

Flexible arms bear suckerless podia that secrete mucus to entrap food and transport it to mouth

Class Ophiuroidea

Class Echinoidea1000 species of sea urchins/sand dollarsMovable spines and podia surround

body; used for locomotionHerbivorous, detrivorous, suspension

feed, a few predators

Class Echinoidea

Unique feeding apparatus called Aristotle’s lantern

Hard plates and muscles just inside mouth

Possesses 5 calcareous teeth

Teeth protract to scrape algae off rocks or tear chunks of kelp

Class Holothuroidea1150 species of sea

cucumbersMucus-covered oral

tentacles trap on plankton or ingest sand organic matter

Gut modified to produce respiratory trees used for gas exchange

Expel portions of these trees as defense mechanism; regenerate