Ch. 38 – Echinoderms Phylum: Echinodermata Sea stars, sand dollars, brittle stars, & sea cucumbers Marine Usually 5 arms pentaradial No circulatory, respiratory, or excretory systems Water-vascular system Tube feet that aid in movement Video Video Video Video
Most invertebrates have an exoskeleton to support them. Echinoderms have an endoskeleton, which is a skeleton within the body. This is why echinoderms are thought to be closer related to vertebrates.
Class: Holothuroidea Sea cucumber Soft body If threatened the sea cucumber may eject their organs out of their body at the predator – called eviscerate. They then regenerate their organs. Video- http://www.youtube.com/watch?v=aCxKFc3XtJs Pg. 784
Class: Echinoidea Sand dollars & sea urchins They have an Aristotle’s lantern, which is a jaw-like structure for grinding their food. Sea urchins have long spines with sometimes venom for protection Sand dollars are about the size of a silver dollar.
Class: Asteroidea (sea star) Body Structure (external) Aboral surface Madreporite is located (top side) Oral surface mouth is located (bottom side) Ossicles calcium spines Pedicellarie tiny little pinchers that clean the body surface so debris doesn’t collect. Video Video
Water- Vascular System Used to create movement Enters the madreporite stone canal ring canal 5 radial canals lateral canal the tube feet (100s of tube feet), have ampulla (air sacs), that act like a pipette and release the water with pressure. Pg. 786
Body Systems No circulatory, respiratory, or excretory systems. Each arm has an eyespot at the end, which senses light and touch. Digestion They have digestive glands. Their tube feet are strong enough to open clams & mussels.
RReproduction Each arm of the sea star has 2 gonads that produce eggs and sperm cells. They are hermaphrodites. SSea stars can regenerate lost parts. A new sea star can regenerate from a segment of an arm as long as it has part of the ring canal attached.