Phylum Echinodermata “spiny” “skin” www.onacd.ca

Sea stars Sea cucumbers Feather stars Sand dollars Sea urchins Brittle stars

Major Classes of Echinoderms ECHINOIDEA: Includes the sea urchins and sand dollars ASTEROIDEA: includes the starfish

OPHIUROIDEA: includes the brittle stars (below: a fossilized brittle star) HOLOTHUROIDEA: includes the sea cucumbers

CRINOIDEA: includes the feather stars

Characteristics of Echinoderms Pentaradial symmetry Have a calcareous skeleton inside their body (endoskeleton) Complete digestive system Open/reduced circulatory system (no heart) with a central ring and vessels

Simple radial nervous system (no brain) Reproductive system consists of gonads which take up a significant amount of space in the body cavity Sexual reproduction with fertilization outside body (most) Have ciliated, free-swimming larvae Possess a water vascular system used for gas exchange, feeding and locomotion

Taking a closer look at Sea Stars Possess 5 or more arms which radiate from a central disk Mouth is located on oral surface (underneath) Found all over the world (very diverse!) Most possess a simple light sensitive eye spot at the end of each arm

Sea stars Spiny projections on the arms Tube feet underneath the arms grip objects, move, and gather food Water vascular system – moves the tube feet

The Water Vascular System A central ring and a series of canals that eventually end in tube feet. Tube feet are used for movement, feeding and bringing in water for gas exchange.

Water vascular system: Water enters through the madreporite Ampulla on the top of the tube foot squeezes water into the tube, making it longer To pull the foot back, the ampulla refills with water, making the foot shorter

Tube feet of a sea urchin! Using muscles to force water into the tube feet extends and pushes them into the ground. The muscles are then relaxed in order for the tube feet to retract.

Digestion Most are predators How to eat a clam (like a sea star): Pry apart the two shells using your tube feet Eject your stomach through your mouth into the clam Digest it inside the shell Pull your stomach back inside. Mmmmm!

Defenses: Pedicellaria, tulip-like pincers that can inject a painful venom Incredible powers of regeneration – can regrow all arms if the central disk remains

Reproduction – They are Dioecious Animals! Asexual - split in half Sexual - mass spawning events

Normal Sea Star

Mutant Sea Star?

Not all sea stars have 5 arms… Sunflower and sun stars have many more. Mutant? Not all sea stars have 5 arms… Sunflower and sun stars have many more.

Crown of Thorns Sea Star Predator of coral polyps Explosions in crown of thorns populations have devastated some coral reefs

Feather, brittle and basket stars Suspension feeders Arms transfer plankton from the water to their mouths

Basket stars are nocturnal and curl up their arms during the day

Basket Star

Brittle Star Will voluntarily break off an arm to escape predation Move quickly (for a sea star)

Feather Stars and Sea Lilies

Feeding arms on a feather star

There may be 5 to 200 arms on a feather star (no tube feet here!).