Echinoderms

EchinodermsEchinoderms““Life with Spiny Skin”Life with Spiny Skin”

Worms, mollusks, and Worms, mollusks, and arthropods all have arthropods all have bilateral symmetrybilateral symmetry..

So do echinoderm So do echinoderm larvae.larvae.

What kind of What kind of symmetry do adult symmetry do adult echinoderms have?echinoderms have?

Radial symmetryRadial symmetryWhat other animal phyla What other animal phyla display radial symmetry?display radial symmetry?

A A RadicalRadical RadialRadial ChangeChange

Bipinnaria larvae (sea star)

Five AliveFive Alive

Most echinoderms Most echinoderms show show pentamerouspentamerous radial symmetry.radial symmetry.

This means there are This means there are usually usually fivefive arms (or arms (or legs) or they are legs) or they are found in multiples of found in multiples of five.five.44

11

5533

22

Spiny Skin – but only the Spiny Skin – but only the skin!skin!

Echinoderm means “Echinoderm means “spiny skinspiny skin.”.” Echinoderms typically have:Echinoderms typically have:

well developed digestive tractswell developed digestive tracts well-developed well-developed coelomcoelom Internal skeleton called an Internal skeleton called an endoskeletonendoskeleton

Spines or bumps are anchored in the Spines or bumps are anchored in the endoskeleton but may protrude endoskeleton but may protrude through the skin.through the skin.

What No Top and What No Top and Bottom?Bottom?

Echinoderms have no head; therefore, there is Echinoderms have no head; therefore, there is no anterior or posterior.no anterior or posterior.

The The echinoderechinoderm m mouthmouth is usually is usually on the on the bottom. bottom. This is This is termed termed the the oral oral side.side.

Rather than Rather than use the use the term term dorsaldorsal, , the side of the side of the the echinoderm echinoderm without a without a mouth is mouth is called the called the aboralaboral side. side.

aboraboralal

oraloral

Water vascular systemWater vascular system A network of water-filled canals that function A network of water-filled canals that function

in movement, feeding, and excretion.in movement, feeding, and excretion.

Water enters the Water enters the echinoderm through echinoderm through the the madreporitemadreporite (mother pore) or (mother pore) or sieve platesieve plate..

Water is then forced Water is then forced through individual through individual tube feettube feet allowing allowing them to move.them to move.

Water Vascular SystemWater Vascular System

Water Vascular SystemWater Vascular System

Types of EchinodermsTypes of Echinoderms Approximately 7,000 species – all marineApproximately 7,000 species – all marine Located from the poles to the tropicsLocated from the poles to the tropics Five major classesFive major classes

AsteroideaAsteroidea (sea stars) – not starfish –they are (sea stars) – not starfish –they are definitely not “fish”definitely not “fish”

OphiuroideaOphiuroidea (brittle stars) (brittle stars) EchinoideaEchinoidea (sea urchins and sand dollars) (sea urchins and sand dollars) HolothuroideaHolothuroidea (sea cucumbers) – not a (sea cucumbers) – not a

vegetable!vegetable! CrinoideaCrinoidea (feather stars and sea lilies) (feather stars and sea lilies)

AsteroideaAsteroidea

Endoskeleton rather flexible to allow for Endoskeleton rather flexible to allow for movement.movement.

Most have five arms radiating from a central Most have five arms radiating from a central disk.disk.

AsteroideaAsteroidea Hundreds of Hundreds of

tube feet are tube feet are found in found in channels channels called called ambulacral ambulacral groovesgrooves radiating radiating from the from the central disk.central disk.

AsteroideaAsteroidea Naturally the Naturally the anusanus is is

on the aboral (top) on the aboral (top) side.side.

Aboral surface Aboral surface covered with covered with pedicellariaepedicellariae – tiny – tiny pincer like organs pincer like organs that keep the sea that keep the sea star clean.star clean.

AsteroideaAsteroidea

OphiuroideaOphiuroidea Brittle starsBrittle stars Most numerous class Most numerous class

of echinoderms.of echinoderms. Characterized by thin, Characterized by thin,

very flexible arms.very flexible arms. Eat particulate matter Eat particulate matter

on the ocean floor.on the ocean floor. No anus.No anus. Often hidden.Often hidden.

Ophiothrix spiculataOphiothrix spiculata

OphiuroideaOphiuroidea

EchinoideaEchinoidea Sea urchins & sand Sea urchins & sand

dollarsdollars Endoskeleton is a Endoskeleton is a

rigid, shell-like “rigid, shell-like “testtest.”.” Covered with movable Covered with movable

spines – used in spines – used in locomotion and locomotion and defense.defense.

Grazers – feed on Grazers – feed on algae and dead algae and dead organic matter.organic matter.

oraorall

aboraboralal

EchinoideaEchinoidea An intricate mouth and jaw system called An intricate mouth and jaw system called

the the Aristotle’s lanternAristotle’s lantern consists of 50 bones consists of 50 bones and is controlled by over 60 muscles.and is controlled by over 60 muscles.

EchinoideaEchinoidea Not all “urchins” have prominent spines.Not all “urchins” have prominent spines. Sand dollars have flattened bodies and tiny Sand dollars have flattened bodies and tiny

spines.spines. They use a mixture of mucus and physics They use a mixture of mucus and physics

(Bernoulli’s principle) to capture food.(Bernoulli’s principle) to capture food.

HolothuroideaHolothuroidea Sea cucumbersSea cucumbers Elongated version Elongated version

of the pentamerous of the pentamerous body plan.body plan.

Lie on side with five Lie on side with five rows of tube feet on rows of tube feet on bottom.bottom.

Tough skin Tough skin supported by supported by calcareous spicules.calcareous spicules.

HolothuroideaHolothuroidea Tube feet near the Tube feet near the

mouth are modified mouth are modified into tentacles for into tentacles for feeding.feeding.

Some burrow and Some burrow and capture food while capture food while others ingest sand others ingest sand and filter out detritus and filter out detritus and small organisms.and small organisms.

HolothuroideaHolothuroidea DefenseDefense

Secrete toxinsSecrete toxins Discharge sticky Discharge sticky

toxic filamentstoxic filaments Eviscerate – eject Eviscerate – eject

a portion of the a portion of the internal organs to internal organs to confuse an confuse an attacker.attacker.

Sea cucumber Sea cucumber eviscerationevisceration

CrinoideaCrinoidea Feather stars, basket stars, Feather stars, basket stars,

sea liliessea lilies Suspension feedersSuspension feeders Oral surface on topOral surface on top Can have from 5 to 200 Can have from 5 to 200

arms!arms! Have claw like appendages Have claw like appendages

that hold the aboral surface that hold the aboral surface to the substrate.to the substrate.

CrinoideaCrinoidea