Phylum Echinodermata Spiny Skin

Advanced?  Skeleton is internal test comprised of individuals plates of porous high-Mg calcite.  Bilaterally symmetrical larvae  Adult typically has pentaradial symmetry  Water vascular system instead of muscles  Highly regenerative – can eviscerate  Separate sexes: External fertilization

Yet simple!  Light sensitive eyes at the end of each ray – no vision, no brain, no head  Reduced internal organs – no respiratory circulatory, excretory, nervous system  Adults have pentamerous radial symmetry  Respiration is by diffusion through skin.

Starfish are scavengers and eat a variety of organisms. They can open a clam shell a few centimeters wide. Then by inverting its stomach into the shell, the clam is digested and absorbed.

Missing parts from injury or evisceration are quickly replaced. Any portion of the central disk will regenerate a new starfish.

The Classes  Crinoidea  Ophiureidea  Holothuroidea  Asteroidea  Echinoidea

Crinoidea ( Feather Stars, Sea lillies)  Upside down brittle star  May have a stalk  Cirri used like a holdfast  Catches food with tube feet  Ancient

Ophiurroidea (brittle star)  Arms distinctly set off from central disk  Tube feet with no suckers. Moves by lashing arms  Closed ambulacral groove, no gut branches in arms.

Holothurudoidea (Sea Cucumber)  Soft, cucumber shaped body  Suckered tube feet in 5 longitudinal rows  Tentacles around mouth (modified tube feet)  Suspension, detritus or deposit feeders

Sea Cucumber Anatomy

Asteroidea (Sea Stars)  Star shaped body  Tube feet with suckers  Open ambulacral grooves  Most have pedicellariae – Thought to be used in defense  Mostly predators  Feed by everting portion of stomach

Sea Star Basic Anatomy

Feeding

Echinoidea (Urchins and Sand Dollars)  Skeleton = test CaCO 3 ossicles are fused  Tube feet with suckers  Moveable spines and pedicellariae  Feed on algae, encrusting animals  Mouth is referred to as Aristotle’s lantern

Sea Urchin

Ecology  Exclusively marine: Echinoderms lack osmoregulatory mechanisms that might allow them to live in brackish or fresh water  Urchins may control algae growth on reefs  Sea Stars are important inter-tidal predators  Make up an estimated 90% of deep sea biomass  May regulate growth of sessile organisms