GENERAL CHARACTERISTICS

• Ex: sea stars, brittle stars, sand dollars, sea urchins, & sea

cucumbers

• All marine

• “Spiny-Skinned Animals” - meaning• Radial Symmetry as adults – 5

parts• Regenerate = Autotomy

GENERAL MORPHOLOGY

• A. INTERNAL SKELETON of calcareous (made of calcium) ossicles (plates)

• Variations :

Brittle / Sea Stars – many small plates that move with one another

Sea Urchin & Sand Dollar – skeleton plates fused into shell called “test”

Sea Cucumber – degenerated & buried in leathery body

B. Water Vascular System

• Network of canals – run throughout body ending w/tube feet

• Varying internal water pressure can extend or contract tube feet

• Tube feet end in small suction cups

• Used in locomotion, food capture, & respiration

C.• Mouth on oral surface

(bottom / ventral)

• Anus on aboral surface (top / dorsal)

ECHINODERM TYPES

SEA STARS• 5 Arms / Rays 4 – 10”

• Prey on bivalves (clams, mussels) & coral

• Many eat w/stomach outside body; pop stomach out mouth

Body Plan

• 2 – 4 rows of tube feet on each ray extend from ambulacral groove

• Have pedicellariae or tiny, forceps-like structures on aboral surface to pick up & remove dirt

Water Vascular System• Water enters

madreporite on aboral surface into a short, straight stone canal

• Stone canal connects to circular canal around the mouth = ring canal.

• Enters five radial canals extending down each arm

Water Vascular System

• Radial canals carry water to hundreds of paired tube feet.

• Bulb-like sacs or ampulla on tube feet contract & create suction

Other Body Systems

• No circulatory, excretory, or respiratory systems

• No head or brain

• Eyespots on the tips of each arm detect light

Reproduction

• Separate sexes

• External fertilization

• Females produce 200,000,000 eggs / season; meroplankton (their larval stage is planktonic)

BRITTLE STARS

• Most mobile; fast

• Snake-like movement

• Disc is .4 – 1.2 “; arms are 2 – 2.4 “• Scavengers

• In the largest class (with basket stars)

• Arms break off readily

BRITTLE STAR LARVA

SEA CUCUMBERS

• Lack arms & visible spines; elongated

• Flexible, leathery body

• Burrowers

• 5 rows of tube feet run length of body

• 10-30 modified tube feet form tentacles

around mouth

• Tentacles have sticky ends to trap plankton; or eat detritus

• Breathes through anus

• Eject internal organs to scare predators (evisceration) ; regenerate in days

•Symbiosis with Pearl Fish which lives in its anus.•Feed on gonads by day

• Filter Feeders

• Can detach & move around

Sea lilies & feather stars

Sea Urchins

• Spines for protection, moving, trapping food

• Shell = test

• Divided into 10 sections• 5 Ambulacral w/tube feet• 5 Interambulacral without

• Covered w/muscle & skin to help mobility

• Tube feet – moving, capturing food

• Pedicellarea – cleaning & defense

• Aristotle’s Lantern – 5 teeth together like bird’s beak; to scrape algae from rocks

Sand Dollars • Flattened version of urchin

• Live in sand along coastlines

• Food falls between dense spines & carried to mouth by cilia & tube feet

        

• Tiny, moveable spines for burrowing

• Aristotle’s Lantern

Sea Biscuits

• Not as flat as dollars

• Live in sand along coastlines;

burrow• Tube feet for respiration• Pedicellarea• Eat detritus in sand   • Short dense spines for

movement cover test