Chapter 16-The Echinoderms

Phylum Echinodermata- Spiny-skinned animals

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Animal Development

AcoelomateAcoelomate- An animal that lacks a coelom, or body cavity.

CoelomateCoelomate- An animal that has a body cavity in which the internal organs are located.

Gastrula stage during embryo development- opening to the outside called a blastopore.blastopore.ProtostomesProtostomes- Animals with mouths that develop from

or near the blastopore; mouth before anusEX: Annelids, Mollusks and Arthropods

DeuterostomesDeuterostomes- Animals in which the anus develops from the blastopore; anus before mouthEX: Echinoderms and Chordates

Embryonic Development

Modern Echinoderms

First animals to develop an endoskeleton Marine, radially symmetrical as adults Evolved more than 650 million years ago Mostly free-living predators; some algae-eaters

Modern EchinodermsAll Echinoderms share four fundamental

characteristics:EndoskeletonEndoskeleton- Calcium-enriched, spine-bearing, and

composed of individual plates called ossiclesossiclesCovered by a thin layer of skin which sometimes wears offSometimes fuse for muscle attachment and shell-like protection

Five-part Radial Symmetry- Mouth on bottom (oral), anus on top (aboral)Bilaterally symmetrical as larvaeArms, called rays, radiate from central point with no head or

brainCan regenerate arms; Complete animal can regenerate from

an arm connected to a portion of the central disk

Pentaradial Symmetry

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Moving Sea Star

Modern EchinodermsWater-vascular systemWater-vascular system- Water-filled system of

interconnected canals and thousands of tiny hollow tube feet Tube feetTube feet with suckers at each end extend outward through

openings in ossicles;used to crawl; each is connected to a water-filled sac called an ampullaampulla

Water enters and leaves through pores in the madroporitemadroporite- a sieve-like structure that filters out large particles

Also functions in feeding and gas exchange- tube feet pull valves of bivalve open to exchange gas and excrete waste

Coelomic circulation and respiration-Skin gillsSkin gills- Small, finger-like projections grow among

spines to create an increased surface area through which gases can be exchanged

Also function as excretory structures

Modern EchinodermsNervous System

Central ring of nerves branches into each arm allowing for independent movement

Radial nerves run along each rayEyespots- at tips of rays, detects light and dark

Digestive systemUses water-vascular system to open bivalvesPushes stomach through mouth into shell (evisceration);

enzymes digest solid food into liquid absorbed by the stomach

Stomach is pulled back into mouth and food travels through intestines where nutrient absorption occurs

ReproductionSeparate sexesGametes located in

arms (rays)Sexual

reproduction- external fertilization

Larvae undergo metamorphosis – bipinnaria larvae

Body Structure

Echinoderm Diversity20 extinct classes; 6

livingSuper-class Stelleroidea

Class AsteroideaSea starsCarnivoresOssicles produce pincerlike

structures called pedicellaria pedicellaria with their own muscles and nerves

Snap at anything that touches them

“Crown-of-thorns” sea star responsible for massive coral reef loss

Echinoderm Diversity

Class OphiuroideaBrittle Stars and Sea

Baskets Largest classSlender, branched arms

that move in pairsBreak easilyThey stay hidden in reefs

and under rocksFilter feeders

Echinoderm Diversity

Class Crinoidea Sea Lilies and Feather Stars Most ancient and primitive Mouth is located on the upper,

rather than lower surface Sessile Feather stars have hook-like

projections to attach themselves directly to the ocean bottom or coral reef

Echinoderm Diversity

Class Echinoidea Sea Urchins and Sand

Dollars Lack distinct arms Sea urchins found on the

ocean bottom Sand dollars live on sand

bars along coasts Spines provide protection

and sometimes contain a venom

Some sea urchins use paralytic toxins

Echinoderm Diversity Class Holothuroidea

Sea Cucumbers

Soft-bodied, slug-like animals without arms

Ossicles small and unfusedMostly separate sexes, some

hermaphroditesMouth surrounded by tube

feet modified into tentacles covered with a sticky mucus

Draws tentacles into mouth to clean off plankton and mucus

Can release sticky threads from anus to trap attackers

Echinoderm Diversity Sea Daisies

Discovered in 1986Strange, disk-shaped

animals with no arms Found off New Zealand

coast Less than 1 cm in

diameterTube feet located

around edge of disk rather than along radial lines

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