PHYLUM ECHINODERMATA

Characteristics: Endoskeleton

Calcareous (calcium carbonate)

Ossicles arise from mesodermal tissue

Pentaradial symmetry as adults

5 sections branch off from disk

Bilateral symmetry as larvae

PHYLUM ECHINODERMATA

Characteristics Water-vascular system

Helps with locomotion, attachment, and feeding

Water-fi lled canals with extensions called tube feet

Includes a ring canal that surrounds the mouth

Complete digestive tract

Nervous system Nerve net Nerve ring Radial nerves

PHYLUM ECHINODERMATA

HistoryShare an ancestor with hemichordates and chordates

Evolved from bilaterally symmetrical ancestors

PHYLUM ECHINODERMATA

Echinoderm AnatomyTube Feet- extensions of the canal system Inside- bulblike ampulla

Contracts & forces water into the tube from the water-filled canals

The tube feet then extend Suction cup at the

distal end Used for locomotion

and/or feeding

PHYLUM ECHINODERMATA

Echinoderm Anatomy Water-Vascular System

Water enters mouth (surrounded by the ring canal)

Ring canal opens to the body through a stone canal (with an opening called a madreporite)

Polian vesicles- sacs connected to the ring canal Function in fluid storage

Canals branch from the ring canal to transport water to the ampulla (internal portion of the tube feet)

PHYLUM ECHINODERMATA

Echinoderm AnatomyHemal system- strands of tissue that encircle the ring canal Circulates fluid using

cilia More than likely helps

to distribute nutrients (definite function is unknown)

PHYLUM ECHINODERMATA

Sea stars1,500 speciesLive on hard

substances, in sand, or in mud

Brightly colored Red, orange, blue, or gray

5 arms- radiate from central disk

Pedicellariae Pincherlike Clean the body surface of

debris Also function in protection

CLASS ASTEROIDEA

Pedicellariae

Maintenance:Diet- snails, bivalves, crustaceans, & corals

Stomach- fills most of the coelom in the central disk 2 regions

Larger, oral stomach (cardiac stomach)- receives ingested food

Smaller, aboral stomach (pyloric stomach)- connects to pyloric cecae (absorb the food)

CLASS ASTEROIDEA

Maintenance Feeding

Force bivalves apart with the tube feet

Clam vs. Sea Star The sea star inserts the

cardiac stomach into the bivalve shell

Gas exchange Diffusion across tissue

Nervous system Nerve ring (encircles the

mouth) Radial nerves extend into the

arms (control the tube feet) Respond to light

(photoreceptors in the arms) & chemicals

CLASS ASTEROIDEA

Reproduction & Regeneration Can regenerate any part

of a broken arm Must at least have a portion

of the central disk remaining Process takes up to a year

to complete Most species are

dioecious 2 gonads in each arm Reproduce externally When one sea star releases

gametes, pheromones stimulate other sea stars to release gametes

CLASS ASTEROIDEA

Basket stars, brittle stars, & serpent stars

> 2,000 speciesLong arms that

give central disk a pentagonal shape

Lack suction disks & ampullasMove like a snake

CLASS OPHIUROIDEA

Sea urchins, sand dollars, & heart urchins

1,000 speciesSea urchins- live on hard

substratesSand dollars & heart

urchins- live in the sand or mud

Move using spines & tube feet

Feed on algae, bryozoans, coral polyps, & dead animal remains

Aristotle’s lantern Chewing apparatus that cuts

food into smaller pieces

CLASS ECHINOIDEA

Sea cucumbers1,500 speciesLack arms- crawl

aroundLack spinesTube feet near the

mouth act as tentacles Covered in mucus to

trap foodProduce toxins to

discourage predators

CLASS HOLOTHUROIDEA

Sea lilies & feather stars

630 speciesSea lilies

Attach permanently to a substrate with a stalk

Crown- unattached end

Feather starsSwim & crawl

Lack nerve ring

CLASS CRINOIDEA