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.

5 Classes of Echinoderms  1. Ophiuroidea  brittle stars & basket stars  2. Crinoidea  sea lilies & feather stars  3. Holothuroidea  sea cucumbers  4. Echinoidea  sand dollars & sea urchins  5. Asteroidea  starfish & sea stars

Class: Ophiuroidea  Brittle stars  Gets it name brittle because its has long, thin arms and are constantly breaking off and regenerating.  Pg 783

Class: Crinoidea  Sea lilies & feather stars  Sessile  Pg. 782

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-  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.

RReproduction  Each arm of the sea star has 2 gonads that produce eggs and sperm cells. They are hermaphrodites. SSea 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.