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

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