Echinoderms Study Notes

Echinoderms Overview

• Phylum: Echinodermata

• Marine, spiny-skinned animals, 6000 species

• Triploblastic deuterostomes

• Body: spiny endoskeleton, secondary radial symmetry

Anatomy of Echinoderms

• Central disk with tapering arms

• Ciliated pigmented epidermis

• Mouth located on oral side

• Ambulacral grooves alongside arms

• Tube feet (podia) along grooves

Class Asteroidea (Sea Stars)

External Anatomy

• Aboral surface rough, features spines

• Pedicellariae for cleaning

• Papulae for gas exchange and waste excretion

• Madreporite connects to water-vascular system

Internal Features

• Endoskeleton of calcareous plates (ossicles)

• Coelom lining is ciliated

• Nervous system: nerve net with central ring and radial nerves

Water Vascular System

• Hydraulic system for locomotion and feeding

• Components: stone canal, ring canal, radial canals

• Tube feet controlled by muscles for movement

Feeding & Digestive System

• Mouth connects to cardiac stomach, pyloric stomach leads to arms

• Carnivorous, primarily feeding on molluscs

Reproductive System

• Dioecious; external fertilization

• Regeneration ability

• Bilateral larva metamorphoses into radial juvenile

Other Classes of Echinoderms

Class Ophiuroidea (Brittle Stars)

• Slender arms, central disk distinct

• No papulae or pedicellariae

• Two-way digestive system, feed on detritus

Class Echinoidea (Sea Urchins)

• Compact bodies within shells (tests)

• Covered with long spines; pentaradial body plan

• Mouth with surrounding teeth

Class Holothuroidea (Sea Cucumbers)

• Ossicles reduced, elongated body

• Tentacles for feeding, cloaca involved in respiration

Class Crinoidea (Crinoids)

• Comprises sea lilies and feather stars

• Stalked or free-living forms; ciliated arms for feeding

• Historical stalk lengths up to 20 m