Phylum Echinodermata Spiny Skin. Advanced? Skeleton is internal test comprised of individuals...
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Phylum EchinodermataSpiny Skin
Advanced?Skeleton is internal test comprised of individuals plates of porous high-Mg calcite. Bilaterally symmetrical larvaeAdult typically has pentaradial symmetryWater vascular system instead of musclesHighly regenerative can eviscerateSeparate sexes: External fertilization
Yet simple!Light sensitive eyes at the end of each ray no vision, no brain , no headReduced internal organs no respiratory circulatory, excretory, nervous systemAdults have pentamerous radial symmetryRespiration 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.
Crinoidea ( Feather Stars, Sea lillies)Upside down brittle starMay have a stalkCirri used like a holdfastCatches food with tube feetAncient
Ophiurroidea (brittle star)Arms distinctly set off from central diskTube feet with no suckers. Moves by lashing armsClosed ambulacral groove, no gut branches in arms.
Holothurudoidea (Sea Cucumber)Soft, cucumber shaped bodySuckered tube feet in 5 longitudinal rowsTentacles around mouth (modified tube feet)Suspension, detritus or deposit feeders
Sea Cucumber Anatomy
Asteroidea (Sea Stars)Star shaped bodyTube feet with suckersOpen ambulacral groovesMost have pedicellariaeThought to be used in defenseMostly predatorsFeed by everting portion of stomach
Sea Star Basic Anatomy
Echinoidea (Urchins and Sand Dollars)Skeleton = test CaCO3 ossicles are fusedTube feet with suckersMoveable spines and pedicellariaeFeed on algae, encrusting animalsMouth is referred to as Aristotles lantern
EcologyExclusively marine: Echinoderms lack osmoregulatory mechanisms that might allow them to live in brackish or fresh water Urchins may control algae growth on reefsSea Stars are important inter-tidal predatorsMake up an estimated 90% of deep sea biomassMay regulate growth of sessile organisms