Echinodermata

“The spiny skinned animals”

Echinoderms

• The spiny skinned animals include these Classes:

1. Class Crinoidea - the crinoids or “feather stars”

2. Class Asteroidea - starfish (sea stars)

3. Class Ophiuroidea - brittle stars, basket star

4. Class Echinodermata - sea urchin, sand dollar

5. Class Holothuroidea - sea cucumbers

Starfish (Asteroidea)

• Carnivores – clams, mussels, bivalves

• Motile by way of tube feet

• endoskeleton made of calcareous plates (ie. Calcium carbonate)

• breathes through dermal “skin gills”

Starfish arm

• Each arm contains a digestive gland and gonads

• The top of the tube feet are called ampulla, like a medicine dropper that is squeezed to create pressure

• Arm will regenerate if torn off = Asexual Reproduction – fishermen learned this the hard way

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

Star fish• The water vascular

system’s opening is called a madreporite. It opens 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.

Ring Canal

Digestive Gland in Arm

Anus

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

Brittle Stars

• These are perhaps the fastest of the echinoderms.

• Most of them are filter feeders or detritus eaters

• Flexible arms, and may be offered as food to get away from predators

Basket Star

Brittle Star

Echinoidea

• Lack arms• eat algae or are

detritus eaters• usually have spines• Gonads prized for

sushi – Bleecker tried this one as a dare and hated it!

Sea Cucumbers• Detritus eaters – the

vacuum cleaners of the sea

• do not have skeletal parts

• will eviscerate if they are scared, meaning offer up internal organs as food to distract predator

Quick Notes on Echinoderm Systems

• Major Body Systems• Digestive – external digestion by lowering

stomach onto prey and releasing enzymes which are absorbed. – Carnivorous Starfish consume such common prey

as…• Snails• Corals• Other echinoderms

– Herbivores such as Sea Urchins consume Algae off rocks

– Filter feeds are Brittle Stars and clean the ocean floor – eg. Brittle Stars

Respir/Circulatory

• Respiration – use of thin walled Tube Feet act as diffusion sites for resp. and also skin Gills in some species.

• Circulatory – due to Simple body plan, and efficient Digestive system, nutrients are carried throughout the body. Circulatory system is not Needed.

Excretory/Motility• Excretion – wastes pass out the Tube Feet. Nitrogen

wastes excreted as Ammonia, out the Anus.

Sensory/Nervous – no Cephalic development. Starfish have up to 200 Light sensitive cells clustered in EyeSpots of each arm. No actual eyes. For balance and hearing, Statocysts or tiny stones pass over hairs to tell the starfish up from down and sense motion or sound by vibrations in the water.

Movement – water pumps system with Tube feet. Suck Water in or out to grasp or release and move.

Reproduction• Reproduction – echinos are either Male or Female. Sperm and

eggs produced in the Testes or Ovaries. Symmetry of a starfish is Radial in adults, meaning if you cut it into a Chunks or many pieces, each slice is the same. Except, in the starfish larvae, they have Bilateral symmetry, just as in advanced critters like Mr. B – okay not that advanced , but you know, they’re trying, okay…

• Asexual Repro – ask a Fisherman and s/he will tell you that tearing starfish into chunks is a great way to Increase their population. Each chunk will undergo regeneration and form new starfish. So, ripping them up is not a great way to reduce predation on Shellfish, which bring in a pretty-penny.