Echinoderms The spiny skinned animals

Introduction Echinodermata are all marine, triploblastic unsegmented coelomates Phylum has 3 unique features: – pentagonal symmetry (bilateral in larvae) –calcite spicules embedded in the skin, often partly fused –Tube feet (podia)

An unhurried phylum.. No echinoderm moves fast, apart from a very few deep sea holothurids which swim actively Crinoids are sessile, the others crawl at a rate of mm / minute During one Antarctic marine survey a starfish was tagged. A year later the same animal was in the same exact spot, having apparently done nothing at all!

5-radial layout Many organ systems in the echinoderms follow the same basic structure as the water-vascular and nervous systems: a 5-radial circum-oral ring These rings give rise to 5 radial branches (canals in the case of the WVS) A few asteroids have 7, 10, 11 arms - in which case 7,10, 11 radial branches

Phylum Echinodermata Echinoderms means “prickly skin” Animals of this phylum include the starfish, sand dollar, sea cucumber and sea urchin. Almost all live in the ocean All adult echinoderms have radial symmetry.

BODY STRUCTURE tube feetAll echinoderms have tube feet - these are hollow structures used for moving and grasping. The tube feet are found on the ventral side of the echinoderm’s arm. Each tube foot looks like a tiny medicine dropper with a suction cup at the bottom.

How echinoderms use their tube feet. 1Water enters an echinoderm through a hole on the top of its body. 2The water then travels through canals in the arms to the tube feet. 3Muscles allow water to move into and out of the tube feet. 4This pumping action enables the suction cups to grasp and release objects and move the echinoderm along

How a starfish eats 1The tube feet help the starfish capture its food. 2A star fish will wrap its arms around a clam attaching the arms to each side of the clam’s shell. 3Eventually the tube feet will pull the shells apart. 4The star fish then forces its stomach out of its body and into the clam shell. 5The stomach digests the clam within the shell.

Surface features Echinoderm skin has several distinctive sets of organs protruding from their skin: –Tube feet (podia) –Spines –Pedicillaria

Gonads Lie as 10 (2N) paired structures at the base of ambulacral grooves. Sexes are separate, and discharge gametes into the sea water Gonads can be large - echinoid gonads almost fill the test, and can be eaten as a delicacy.

Sadly... Of the 13 classes of echinoderms known, 7 are extinct. Echinoderms were dominant forms in Carboniferous seas, but have suffered a long-term decline in phyletic richness

Echinoderms The spiny skinned animals include: –Class Crinoidea - the crinoids –Class Asteroidea - starfish (sea stars) –Class Ophiuroidea - brittle stars, basket star –Class Echinoidea - sea urchin, sand dollar –Class Holothuroidea - sea cucumbers

Crinoids Filter feeders some are sessile some are motile They were very common in the Paleozoic Their bodies are often found in limestone deposits

Crinoid Arm

Star fish (sea star) Carnivores motile move on tube feet endoskeleton made of calcareous plates (ie. Calcium carbonate) breathes through dermal “skin gills”

Star fish The water vascular system’s opening is called a madreporite. It opens into a vertical stone canal. The stone canal empties into a radial canal. The radial canal then goes out to the arms in radial canals. The radial canals then feed water to the tube feet.

Starfish arm Each arm contains a digestive gland and gonads The top of the tube feet are called ampulla

Starfish The eye of the starfish is at the end of the arms. (It is often red coloured) The anus of the starfish is on the top (aboral side) The mouth piece of the starfish is called “Aristotle’s Lantern”.

Tube Feet and Mouth

Sunstar

Brittle Stars These are perhaps the fastest of the echinoderms. Most of them are filter feeders or detritus eaters

Basket Star

Brittle Star

Echinoidea Lack arms eat algae or are detritus eaters usually have spines are protected by pedicellarae

Sea Heart Sea Hearts are found in the mud of muddy beaches.

Sea Cucumbers Detritus eaters do not have skeletal parts will eviscerate if they are scared