30. Echinodermata

Introduction to Spiny-skinnedSea Animals

Apparent Radial Symmetrycompare Hickman Fig. 23-3

like spokes of a wheel

sea star

Secondary Radial Symmetry

•ancestors were bilateral– larvae are initially bilateral

– but radial after metamorphosis

•oral-aboral axis – not original anterior-posterior

– but from embryo’s left-right axis

bipinnaria larva of starfish, left side

Compare Hickman Fig. 23-9

posterior

anterior

ventral dorsalfood

Starfish MetamorphosisCompare Hickman Fig. 23-9

bipinnaria

brachiolaria

oral

aboral

attachment stalk is lost later

developing arms of adult

Echinoderm Habitat

• entirely marine• larvae are planktonic and Bilateral• adults are entirely benthic

– radial body plan is best for sessile life style• radial symmetry of echinoderms is evidence

that their ancestors were sessile– but most adults can crawl, and tend back

toward bilateral symmetry

Water Vascular System• unique to echinoderms• used for locomotion and food-gatheringComponents:• madreporite for water exchange• hydraulic tubing:

– stone canal, ring canal, radial canals• tube feet with internal ampullae

Starfish AnatomyFig 23-3

bony internal skeleton

cardiac stomach

pyloric stomach

elements of water vascular system

Tube Feet of Sea Star(similar in sea urchins and sea cucumbers)

equipped with: internal ampulla,valves, and many tiny

muscles

connector to a radial canal

Sea Stars Are CarnivoresFig. 23-5

Skeleton and Skincompare Hickman Fig. 23-4

• bony endoskeleton and spines • pedicellariae

– tiny pincers on stalks– for defense and feeding

• many, tiny gills

bony ossiclebony spine

gillpedicellaria

Sea Urchin Pedicellariae(also in sea stars)

compare Hickman Fig. 23-4

zoologist’s forceps

barnacle larvasea star’s tube feet

Reproduction

• mostly sexual, adults diecious• sea stars can regenerate severed arms • some kinds can break apart and re-grow into two

sea star, regenerating

armsHickmanFig. 23-8

Echinoderm Classes

Variations on EchinodermBody design

Classificationabout 6,000 species

• Asteroidea - sea stars, or starfish• Echinoidea - sea and heart urchins, sand dollars• Ophiuroidea - brittle, serpent, and basket stars• Crinoidea - sea lilies, feather stars• Holothuroidea - sea cucumbers

Asteroidea - Sea Stars or StarfishFig. 23-1

Echinoideacompare 23-16,17,18,19

sea urchin sand dollar

some have poisonous spines

Sea Urchin Anatomy

Hickman Fig. 23-19

Aristotle’s lantern(five jaws, for scraping algae)

Ophiuroidea - Brittle or Serpent Starscompare 23-14

Scavengers and passive suspension-feeders

Brittle Star AnatomyHickman Fig. 23-12,13

madreporiteon oral side

blind gut

ventral view of disk

lateral, cut-away view of disk

Crinoidea - Feather Stars or Sea LiliesHickman Fig. 23-25

passive filter-feeders

Model of Paleozoic, Crinoid “Garden”

Feather Star Anatomy

arms

pinnules(tube feet that

catch food particles)

mouth

pinnules

cilia cause mucus flow

Holothuroidea- Sea Cucumberscompare 23-23,24

deposit-feeder

suspension-feeder

tentacles tube feet

Sea Cucumber AnatomyHickman Fig. 23-23

dissected

tube feet

radial canals intestine

oral (“anterior”)

aboral (“posterior”)