phylum echinodermata - mhhs 2016-2017 - phylum echinodermata •“spiny skinned” or “hedgehog...
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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 (dont 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
Aristotles 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