Echinoderms Phylum Echinodermata

• “spiny skinned” or “hedgehog skin”

• sea stars (starfish), sea urchins, sea cucumbers

• 6000 species

• radial symmetry in 2o development

• bilateral symmetry in larva

http://www.biologyreference.com/Dn-Ep/Echinoderm.html

• most have pentamerous radial symmetry = based on 5 parts

• live on ocean bottom – slow bottom crawlers

• have no head

• no anterior or posterior side oral

and aboral

• complete digestive tract

• internal endoskeleton – secreted w/in tissues – may be covered by a thin layer of ciliated tissues

Digestion • mostly carnivorous

• feeds by extending/everting part of stomach inside out thru mouth – secreting digestive enzymes – carries food back into mouth

• guts may be very short (starfish or sea cucumber) or very long (sea urchins)

• longer guts are needed to digest plant particles

• nutrients are transported in fluid called coelemic fluid in the coelem

Circulatory system/gas exchange

• O2 is transported via coelemic fluid

• Lacks a true circulatory system

• Gas exchange occurs in small, branched projections of the body wall connected to coelemic cavity

• Sea cucumbers have respiratory trees pair of thin branched tubes

that are extensions of gut and are suspended in coelem by coelemic fluid they draw in water and

provide increased surface area for gas exchange

Nervous system

• have a nerve net

• coordinates tube feet and spine mvmt.

• no brain

Reproduction

• dioecious

• may have 5-10 gonads located in body cavity

• all species spawn at once to better insure fertilization in which eggs and sperm are simply released into water

• fertilized egg develops into plankton as a ciliated larva (bilaterally symm.)

• asexual reproduction by regeneration ability to grow back lost/damaged parts

Class Asteroidea

• Sea stars, a.k.a. starfish

• 5 arms radiating from a central disk with eyespot at each end that is sensitive to light

• hundreds of tube feet with suckers protrude from oral surface along ambulacral groove

• move in any direction very slowly

Class Asteroidea

• have pedicellariae = modified spines that are pincer-like organs – used to clean the surface

• have a water vascular system – use as others use muscles

• predators of bivalves, snails, barnacles, other slow moving animals

• Ex. Asterias

Class Ophiuroidea

• Brittle stars

• 2000 species

• very long and flexible arms

• arms move in snake-like motion for locomotion (most mobile echinoderm!)

• tube feet have no suckers and are used for feeding

• feed on organic matter and small animals picked up from the bottom (most are scavengers)

Class Ophiuroidea • food is picked up by tube feet and

passed to the mouth

• hide under rocks, coral, or cover up with mud/sand (don’t like light!)

• ex. spiny brittle star – Ophiothrix angulata – found subtidally from Chesapeake Bay to Florida

• Ophioderma brevisipina – lives in shallow water from Cape Cod to Florida

Class Echinoidea

• Sea urchins and sand dollars

• 900 species

• endoskeleton forms a rigid test w/ movable spines and pedicullariae

• possess a water vascular system

• move by spines jointed to sockets in the test and suckers at the tip of each tube foot

• 5 rows of ambulacral grooves w/ tube feet extending from pole to pole w/ mouth on the bottom and anus on top

Class Echinoidea • System of jaw & muscles called

Aristotle’s lantern used for biting off algae

• omnivores

– graze on attached or drifting plant material

– ingest encrusting animals (like sponges and bryozoans) and dead organic material

• very common on rocky shores

• when it dies, it leaves behind the test • ex. Eucidarias tribuloides - Carolinas to Florida – very

thick and blunt

• ex. Mellita quinquiesperforta - sand dollars found from Cape Hatteras (NC) to Florida – yellow-brown in color – bring food to mouth as they walk - small particles of food are “chewed” by dentary apparations - rattles when skeleton is shaken – eaten by sea stars, flounder and cod

Class Holothiuroidea

• Sea cucumbers

• worm-like – no spines - no radial symmetry

• usually lies on one side w/ mouth at one end and anus at the other

• endoskeleton has microscopic calcareous spicules throughout warty skin

• have 5 rows of tube feet extending from mouth to anus

• are deposit feeders

Class Holothiuroidea

• tube feet around mouth are branched tentacles that pick up organic matter

• may secrete toxic chemicals or discharge sticky filaments thru anus as defense

• may expel gut and internal organs thru the mouth/anus = evisceration (extending the gut to distract the offender) – sea cucumber regrows any lost parts w/in 6 wks. – messy but effective

Class Holothiuroidea

• ex. Leptosynapta – “snot” sea cucumber – no tube feet – located all over the whole coast – consumes detritus as it burrows

• ex. Sclerodactyla briareus – “hairy” sea cucumber - Cape Cod to Gulf of Mexico – covered by slender tube feet

• Japanese cook in soy sauce and ginger – in China dry it and is a gourmet delicacy

Class Crinoidea

• Feather stars and sea lilies

• Suspension feeders that use outstretched feathery arms to obtain food from water

• 600 species

• some are restricted to deep water and attach to bottom (sea lilies)

• come crawl on hard bottoms in shallow water to deep water in tropical Pacific and Indian Oceans (feather stars)

Class Crinoidea

• resemble upside down brittle stars w/ ambulacral grooves and mouth upwards

• larger organs are restricted to a small cup-shaped body from which arms radiate

• may have from 5-200 arms w/ possible side branching

• side branches have tiny tube feet that secrete mucus to aid in food catching