Echinoderm Classes Asteroidea – Sea Stars : Multiple arms radiating from central disk Tube feet on bottom Ophiuroidea – Brittle Stars: Distinct central disk with snake like arms Tube feet lack suckers

Echinoderm Classes Echinoidea – Sea Urchins and Sand Dollars: No arms, but 5 rows of tube feet Have muscles that can move spines graphyiles/ Crinoidea – Feather Stars and Sea Lilies Flexible arms used in suspension feeding Haven’t changed in 500 million years

Echinoderm Classes Holothuroidea – Sea Cucumbers Reduced endoskeleton Five rows of tube feet Concentricycloidea – Sea Daisies Only two known species Disk shaped, less than 1cm in diameter

Echinoderm Sensory Structures Eyespots on the ends of arms are sensitive to light Tube feet, and spines are sensitive to touch

Echinoderm Reproduction Sexual: Eggs and sperm are released into the water where they are fertilized Larvae are planktonic Asexual: Echinoderms can regenerate body parts and organs Asexual reproduction can occur if the echinoderm is torn with enough of the body on each part erfig.gif

Body Symmetry All adult echinoderms exhibit radial symmetry For the most part… LARVAE are bilateral ADULTS are radial wiki/Echinoderm

Excretory System Main opening of a echinoderm is used only to EXPEL WASTE Anus leads directly from stomach Anus is on the top, Mouth is on the bottom universe-review.ca

Skeletal Type Echinodermata: “Spiny Skinned” DO NOT possess an exoskeleton a thin outermost skin covers a type of endoskeleton made of tiny calcified plates and spines Skeleton composed of skeletal plates called ossicles

Skeletal Type Echinodermata: “Spiny Skinned” Ossicles = small bones In some species, such as the sea urchin, plates of the skeleton are locked together to form a rigid structure. most sea stars and brittle stars can flex their ‘arms’

Other Unique Features Echinoderms can REGENERATE Water vascular system (described earlier) is unique to echinoderms; varies water pressure to control tube feet

Other Unique Features Crinoids and some brittle stars are filter-feeders Sea urchins = grazers Sea cucumbers = deposit feeders Starfish = active hunters

More Unique Features Autonomy = The spontaneous self amputation of an appendage when the organism is injured or under attack. The autotomized part is usually regenerated.

Nervous System Decentralized central nerve ring surrounds gut, connects radial nerves. Radial nerves run under each arm, coordinate movement, etc. Do not have “brains,” but some have ganglia along radial nerves

Digestive System Complete digestive system (tubular gut), mouth to anus. (bottom to top)

Locomotion/Musculature Utilize water vascular system and tube feet Water in from madreporite, pumped into ampulla by radial canal

Locomotion/Musculature Ampulla contracts, water to podia Podia contracts, water to ampulla – Podia bend and shorten – Allows movement

Gas Exchange Mostly gill-like structures

Circulatory System Utilize a s eries of canals and spaces to distribute nutrients. No respiratory system. echinodermata.html echinodermata.html

Quiz 1. Echinodermata have ________ symmetry as larvae, but display ________ symmetry as adults. 2. What allows Echinoderms to function in locomotion, feeding and gas exchange? 3. Sea stars can grow new arms and sea cucumbers can replace their gut after ejecting them. What feature of echinoderms does this demonstrate? 4. Name the stomachs of a sea star. Functions?

Answers Bilateral, radial Water vascular system Regeneration Cardiac, pyloric; evert and enzymes, further digestion