Echinoderms

Echinoderms

Spiny skin animals
Pentaradial symmetry
Water vascular system

Class Asteroidea (sea stars)

Central disk with 5 arms (organs in them)
Thin epidermis, oral mouth and aboral (non functional) anus

Protrusions of sea stars

Ossicles of endoskeleton protrude as blunt spines

Sea star movement

Podia/ tube feet

Sea star feeding

Double stomach (pyloric and cardiac)
Cardiac stomach emerges through mouth to digest prey

Sea star sexual reproduction

Gonads located on each arm

sea star asexual reproduction

By regeneration of arms
They re grow arms often

Some sea stars are keystone predators

Keep dominant competitors under control

Class Ophiuroidea (brittle stars)

Slender arms around central disk
Arms do not hold visceral organs (inside central disk)

Britte sea star jaws

Four

Brittle star tube feet

Reduced, used for assisting feeding only (not for movement)

Brittle star feeding

Scavengers

Brittle star spines

Short spines located on disk and along the arms

Why do brittle stars have flexible arms

For locomotion

Brittle star habitat

Rock and sandy, deep seafloors

Brittle star sexual reproduction

Adults spawn gametes, egg external fertilization, hatch larvae and settle as juveniles

Brittle stars asexual reproduction

High regeneration capacity: can regrow arms and part of the central disk

Autotomy

The cut or release of body parts to escape predators

Class Echinoidea (sea urchins, sand dollars)

Visceral organs in central disk, dorsal anus
Red gonads on top, digestive glands below
Ossicles become larger and fussed

Sea urchins

Spines become long and moveable (defence)
Locomotion is still based on podia (tube feet)

Sea urchin diet

Omnivores but most are herbivores

Aristotle's lantern

Chewing organ (scrape algae using 4

Sand dollars

Flat shape with reduced movable spines
Use their spines to food towards mouth

Sand dollar habitat

Soft bottoms (sandy sediments)

Sand dollar feeding

Deposit feeders

Echinoidea reproduction

Sexual

Class Holothuroidea (sea cucumbers)

No arms
Oral

Sea cucumber locomotion

Five grooves with tube feet

Sea cucumber feeding

Tentacles around mouth
Scavengers

Sea cucumber sexual reproduction

Production of eggs, external fertilization, hatch larva, settling of a juvenille

Class Crinoidea (sea lilies and feather stars)

Leather skin with plates
Mouth and anus faces upward

Class crinoidea feeding

Filter feeding: tentacles move the water and have mucus to help trap food

Class crinoidea sexual reproduction

Planktonic larva

Class crinoidea asexual reproduction

High regeneration capacity

Hemichordata (acorn worms)

Body divided in proboscis, collar and trunk

Acorn worm respiration

Gill pores/ slits

Hemichordates have similar larvae to

Sea stars

Acorn worms share gill morphology with

Chordates