Phylum Echinodermata Echinoderms Sea Stars Sea Urchins Sand

Phylum Echinodermata

Echinoderms • • Sea Stars Sea Urchins Sand Dollars Sea Cucumbers

Echinoderms • “Spiny Skin” • 7, 000 species • Marine Environments – Shallow and deep waters • Vary in size – From 1 cm to 1 m (3 feet) • Often brilliantly colored

Echinoderms • Radial Symmetry – Like cnidarians and ctenophores • Lack cephalization • Larvae are bilaterally symmetrical Sea Star Brittle Star Sea Urchin

Echinoderms • Echinoderms are deuterostomes, which makes them different from all of the other invertebrates • Deuterostomes are coelomates whose 1. 2. 3. embryos have radial cleavage anus forms near the blastopore mesoderm arises from outpockets of the endoderm

Echinoderms Have: • Pentaradial symmetry – the body parts extend from the center along five spokes • An endoskeleton composed of calcium carbonate plates • Many small, movable extensions of the water-vascular system called tube feet, which aid in – – Movement Feeding Respiration Excretion

Echinoderm Classification • CLASSES: – Crinoidea (kri-NOID-ee-uh) – Asteroidea (AS-tuh-ROID-ee-uh) – Ophiuroidea (OH-fee-yoor-OID-ee-uh) – Echinoidea (EK-uh-NOID-ee-uh) – Holothuroidea (HOH-loh-thuh-ROID-ee-uh)

Class Crinoidea • “lily-like” • Examples: sea lilies, feather stars – Five arms extend from the body and branch to form many more arms – Tube feet gas exchange – Cilia on arms direct food to the mouth – Mouth faces up

Class Ophiuroidea • “snake-tail” • Examples: basket stars and brittle stars – Long, narrow arms help them move quickly • Can break and regenerate easily – Live on the ocean’s floor – Either rake in food with arms or trap it with their tube feet or mucus between their spines

Class Echinoidea • “spinelike, ” • Examples: sea urchins, sand dollars – Test –compact, rigid endoskeleton – Urchins: • Five teeth + their muscles = Aristotle’s Lantern • Spines can be sharp and contain venom – Sand dollars: • Burrows into the sand • Use spines for locomotion and burrowing

Aristotle’s Lantern

Class Holothuroidea • “water polyp” • Examples: sea cucumbers – Soft bodies because the particles that make up their endoskeleton are small – Use tentacles to bring food to the mouth

Sea Cucumbers • Eviscerate their gut as a means of self defense

Class Asteroidea • “starlike” • Examples: sea stars – Live in coastal waters around the world – Prey on oysters, clams, and other foods humans eat

Structure and Function • Sea stars typically have 5 arms, but in some species, there may be as many as 24 • Two rows of tube feet run along the underside of each arm

Structure and Function • On sea stars and sea urchins, pedicellariae or little pincers, help keep the body surface free of foreign objects, including algae and small animals that might damage its soft tissues

Structure and Function • Gas exchange and waste excretion take place by diffusion through the skin gills,

Structure and Function • • • Primitive nervous system No head = no brain The nervous system consists mainly of a nerve ring that circles the mouth and a radial nerve that runs from the nerve ring along the length of each arm • Together, they coordinate the movements of the tube feet

Structure and Function • Sea stars also have a nerve net near the body surface that controls the movements of the spines, pedicellariae, and skin gills. • Eyespot on each arm responds to light • Tube feet respond to touch and chemicals

Water-Vascular System Madreporite-water enters through this small pore Madreporite Stone canal -connects madreporite and ring canal Radial canal -extends down each arm and carries water to hundreds of hollow tube feet---has valves to ensure one way flow

Feeding and Digestion • Most echinoderms are carnivores. • A sea star captures a clam and attaches to both shells with its tube feet, eventually tiring the clam’s muscles. Once the shell is opened every so slightly, the sea star ejects a portion of its stomach into the clam to digest the tissue. • The sea star ejects a portion of its stomach when it feeds. • Waste is expelled through anus on aboral surface.

Reproduction • Most echinoderms are dioecious. • Fertilization occurs externally after the organisms spawn. • A free-swimming larva called a bipinnaria results and eventually develops into an adult. • As long as a portion of the central ring remains intact, a sea star can regenerate

Regeneration

Which Class? Asteroidea Crinoidea Echinoidea Ophiuroidea Holothuroidea