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Echinodermata. Riley Galton Julia Heunis David Lin. Riley Galton. Echinoderm Classes. Asteroidea – Sea Stars : Multiple arms radiating from central disk

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Riley Galton

Julia Heunis

David Lin

Echinoderm classes

Riley Galton

Echinoderm Classes

Asteroidea – Sea Stars:

  • Multiple arms radiating from central disk

  • Tube feet on bottom

Ophiuroidea – Brittle Stars:

  • Distinct central disk with snake like arms

  • Tube feet lack suckers

Echinoderm classes1

Riley Galton

Echinoderm Classes

Echinoidea – Sea Urchins and Sand Dollars:

  • No arms, but 5 rows of tube feet

  • Have muscles that can move

  • spines

Crinoidea – Feather Stars and Sea Lilies

  • Flexible arms used in suspension feeding

  • Haven’t changed in 500 million years

Echinoderm classes2

Riley Galton

Echinoderm Classes

Holothuroidea – Sea Cucumbers

  • Reduced endoskeleton

  • Five rows of tube feet

Concentricycloidea – Sea Daisies

  • Only two known species

  • Disk shaped, less than 1cm in diameter

Echinoderm sensory structures

Riley Galton

Echinoderm Sensory Structures

  • Eyespots on the ends of ambulacra are sensitive to light

  • Pedicellariae(jaw like skeletal structures used to keep organisms from settling on skin),tube feet, and spines are sensitive to touch

Echinoderm reproduction

Riley Galton

Echinoderm Reproduction


  • Eggs and sperm are released into the water where they are fertilized

  • Larvae are planktonic

  • Internal fertilization has been observed in certain species of sea stars, brittle stars, and sea cucumbers


  • Echinoderms can regenerate body parts and organs

  • Asexual reproduction can occur (though not by will) if the echinoderm is torn with enough of the body on each part

Body cavity coelom

Julia Heunis

Body Cavity (Coelom)


  • Coelom = A fluid-filled cavity between body wall and gut; lined by mesoderm

  • Two parts:

    Perivisceral coelom – large, fluid-filled cavity where major organs, digestive tube and sex organs, are suspended

    Water Vascular System - network of hydraulic canals unique to echinoderms that branches into extensions (tube feet) which function in locomotion, feeding and gas exchange

Body symmetry

Julia Heunis

Body Symmetry

  • evolved from animals with bilateral symmetry

  • adult echinoderms possess radial symmetry

  • All echinoderms exhibit fivefold radial symmetry in portions of their body at some stage of life (5 parts around central axis), even if they have secondary bilateral symmetry

  • For the most part…

    LARVAE ~ bilateral

    ADULTS ~ radial

Excretory system

Julia Heunis

Excretory System

  • NO true excretory system!

  • Main opening of a sponge used only to EXPEL WASTE

  • Anus leads directly from stomach/digestive tract

  • Anus = top

    mouth = bottom

Olivia Heunis

Skeletal type echinodermata spiny skinned

Julia Heunis

Skeletal TypeEchinodermata: “Spiny Skinned”

  • DO NOT possess an exoskeleton

  • a thin outermost skin covers a mesodermal endoskeleton made of tiny calcified plates and spines - forms rigid support contained within tissues of the organism

  • Skeleton composed of skeletal plates called ossicles

  • Ossicles = small bones

  • In some species, such as the sea urchin, plates of the skeleton are locked together to form a rigid structure.

  • most sea stars and brittle stars can flex their ‘arms’ = skeleton has gaps, flexible plate junctures

Other unique features

Julia Heunis

Other Unique Features

  • Echinoderms can REGENERATE

    ex: sea cucumbers can eject a portion of gut in response to predators and regenerate when safe

  • Water vascular system (described earlier) is unique to echinoderms; varies water pressure to control tube feet

  • Crinoids and some brittle stars = passive filter-feeders, absorbing suspended particles from passing water

    sea urchins = grazers

    sea cucumbers = deposit feeders

    starfish = active hunters

More unique features

Julia Heunis

More Unique Features

  • Autonomy = The spontaneous self amputation of an appendage when the organism is injured or under attack. The autotomized part is usually regenerated.

  • “arms” → multiples of 5; some have more because of regeneration

  • mutable collagenous tissue ~ connect ossicles; can maintain different positions without much effort

Nervous system

David Lin

Nervous System

  • Decentralized

  • central nerve ring surrounds gut, connect radial nerves.

  • Radial nerves run under each arm, coordinate movement, etc.

  • Do not have “brains,” but some have ganglia along radial nerves

Digestive system

David Lin

Digestive System

  • Complete digestive system (tubular gut), mouth to anus. (bottom to top)

  • Crinoidia: filter-feed, use cilia

  • Asteroidea: Cardiac (evert), pyloric stomach, digestive glands

  • Urchins: “Aristotle’s lantern” (masticatory apparatus)

  • Holothurians: suspension/deposit feeders, use tentacles.

Locomotion musculature

David Lin


  • Utilize water vascular system and tube feet

  • Water in from madreporite, pumped into ampulla by radial canal

  • Ampulla contracts, water to podia

  • Podia contracts, water to ampulla

    • Podia bend, shorten allows movement (vacuum and suction)

Gas exchange

David Lin

Gas Exchange

  • Asteroids, crinoids: dermal gills (thin epidermis)

  • Urchins: infolds of body wall (bursae) opening to outside

  • Sand dollars: modified podia on top (petaloids) which are thin-walled and flaplike.

  • Holothurians: highly branched hindgut called "respiratory tree"

Circulatory system

David Lin

Circulatory System

  • Mostly in perivisceral coelom, enhanced by water vascular system and hemal system.

    • Hemal system: series of canals and spaces mostly in coelomic channels. Fluid movement by cilia. Used to distribute nutrients. No respiratory system.


  • Echinodermata have ________ symmetry as larvae, but display ________ symmetry as adults.

  • What allows Echinoderms to function in locomotion, feeding and gas exchange?

  • Sea stars can grow new arms and sea cucumbers can replace their gut after ejecting them. What feature of echinoderms does this demonstrate?

  • Name the stomachs of a sea star. Functions?


  • Bilateral, radial

  • Water vascular system

  • Regeneration

  • Cardiac, pyloric; evert and enzymes, further digestion