Echinoderms

"Echinoderm Form, Function and Locomotion Feeding" and "Reproduction in the Echinoderm"

What does the name "Echinoderm" mean?

Spiny skin.

How many echinoderm species are currently living?

About 7,000.

Name the five main living echinoderm classes.

Asteroidea, Ophiuroidea, Echinoidea, Holothuroidea, Crinoidea.

Where are echinoderms found?

Exclusively in marine environments, from intertidal zones to deep oceans.

What kind of symmetry do adult echinoderms show?

Radial pentamerous symmetry.

What type of body cavity do echinoderms have?

Coelomate with four coelomic systems.

Name the four coelomic systems in echinoderms.

Perivisceral coelom, haemal system, peri-haemal system, water vascular system.

What type of skeleton do echinoderms have?

Endoskeleton made of ossicles held by catch collagen.

What is the symmetry of Asteroidea?

Pentamerous radial symmetry.

What structures are found in the arms of Asteroidea?

Ambulacral grooves, tube feet, papulae, sensory tentacles, eyespots.

What are papulae in starfish?

Projections of the coelomic cavity that function as gills.

What is the function of the madreporite?

It allows water into the water vascular system.

How many arms do sun stars have?

More than 40.

Where are pedicellariae located in starfish?

On the aboral surface.

What distinguishes Ophiuroidea from Asteroidea?

Distinct central disc and slender arms with no ambulacral grooves.

How do brittle stars move?

They crawl using their flexible arms.

Do brittle stars use their tube feet for locomotion?

No, they use arms instead.

What is the function of bursae in brittle stars?

Gas exchange and possibly reproduction.

How are echinoid skeletons different?

Ossicles are fused to form a rigid test.

What are the ambulacral and interambulacral regions in echinoids?

Ambulacral regions have tube feet, interambulacral do not.

How do regular and irregular urchins differ?

Regular urchins are radially symmetrical with long spines; irregular are bilaterally symmetrical with short spines.

How do regular echinoids move?

Using tube feet.

How do irregular echinoids move?

Using short spines.

What is the role of the peristomal gills in echinoids?

Oxygen transfer to muscles and organs.

How do holothurians move?

Using tube feet and body wall muscle contractions.

What is the main body orientation in sea cucumbers?

Elongated oral-aboral axis with bilateral symmetry.

Do sea cucumbers have spines?

No, they lack spines and pedicellariae.

What is the respiratory tree in holothuroids?

An internal structure connected to the cloaca used for gas exchange.

What is evisceration in sea cucumbers?

A defensive process where internal organs are expelled.

What are Cuvierian tubules?

Sticky or toxic threads expelled for defence in some holothurians.

What distinguishes Crinoidea from other echinoderms?

They are mostly sessile or slow-moving, with the mouth facing upwards.

How do feather stars move?

By crawling or short-distance swimming using their arms.

What are pinnules in crinoids?

Sub-branches of arms bearing tube feet for feeding.

Where is the water vascular system madreporite located in crinoids?

They lack a madreporite.

How is gas exchange achieved in crinoids?

Through tube feet.

What are the main functions of echinoderm spines?

Protection, defence, wave dissipation, and sometimes toxin delivery.

What are echinoderm spines made of?

Ossicles, typically rod-shaped.

How are echinoid spines articulated?

With ball-and-socket joints controlled by muscles and catch collagen.

What is catch collagen?

A connective tissue that stiffens to hold spines without constant muscular effort.

What are pedicellariae?

Small pincer-like structures used for cleaning and defence.

On which echinoderm groups are pedicellariae found?

Asteroidea and Echinoidea.

What are the main types of pedicellariae?

Tridactyl, ophiocephalous, trifoliate, gemmiform.

How do crinoids perform locomotion?

By crawling or swimming with arm movements.

How do ophiuroids perform locomotion?

By coordinated arm movement, not using tube feet.

How do regular echinoids move?

Using tube feet extended beyond the spines.

How do irregular echinoids move?

Primarily using short spines.

How do holothurians burrow?

With muscular contraction and tube feet on their ventral side.

What is the primary locomotion method in asteroid starfish?

Movement via the water vascular system and tube feet.

How does water enter the WVS?

Through the madreporite.

List the flow of water through the WVS.

Madreporite → stone canal → ring canal → radial canals → lateral canals → ampullae → tube feet.

What do the ampullae do?

Contract to push water into tube feet, causing extension.

How are tube feet retracted?

Retractor muscles contract and water is pulled back into ampullae.

What allows starfish tube feet to adhere to surfaces?

Chemical secretions for adhesion and detachment.

Do all tube feet move in unison?

No, they operate in waves for coordinated movement.

Do asteroid tube feet function as respiratory structures?

Yes, they aid in oxygen transfer.

What are the primary feeding methods of asteroids?

Carnivory and scavenging, with some species acting as suspension feeders.

How do asteroids consume prey like bivalves?

They pry shells open with tube feet and evert their stomachs to digest the prey externally.

What is the role of catch collagen in asteroid feeding?

It allows the starfish to hold bivalve shells open without muscle effort.

How do ophiuroids feed?

They use suspension feeding, deposit feeding, and predation/scavenging.

How do ophiuroids perform suspension feeding?

They wave mucus-covered arms to create water currents and catch particles.

How do ophiuroids capture small prey?

They use their flexible arms to catch crustaceans or worms.

What are the feeding strategies of regular echinoids?

Mostly herbivorous, grazing on algae with Aristotle's lantern.

What do irregular echinoids feed on?

They are primarily deposit feeders.

What is Aristotle's lantern?

A jaw apparatus with five ossicles used by echinoids to scrape and grind food.

How did the crash in Diadema antillarum affect coral reefs?

It led to algal overgrowth due to loss of herbivory.

How are crinoids classified in terms of feeding?

Passive suspension feeders.

How do crinoids capture food?

With mucus-covered tube feet between pinnules.

How do holothuroids feed?

By deposit or passive suspension feeding using mucus-covered buccal podia.

How do deposit-feeding holothuroids collect food?

They ingest sediment using shovel- or tentacle-shaped podia.

Can echinoderms use more than one feeding method?

Yes, some groups like ophiuroids and holothuroids use multiple feeding strategies.

Which echinoderm groups reproduce asexually?

Asteroids, ophiuroids, and holothuroids.

What are the main methods of asexual reproduction?

Fission and autotomy.

What is fission in echinoderms?

Splitting the body into two parts, often along a fission plane.

What is autotomy?

Breaking off part of the body (e.g. arm), which then regenerates into a full animal.

What are the drawbacks of asexual reproduction?

Low dispersal, lack of genetic diversity, and energy cost.

Which asteroid is obligately fissiparous?

Stephanasterias albula, which lacks gonads.

What part of the body must remain for regeneration by autotomy?

At least one fifth of the central disc.

How do holothuroids perform fission?

By twisting and stretching their bodies to split.

What is the dominant reproductive mode in echinoderms?

Sexual reproduction with external fertilisation.

Do any echinoderms have hermaphroditic individuals?

Yes, in some starfish and brittle stars.

Where are gonads located in echinoderms?

In arms, bursae, pinnules, or interambulacral regions, depending on the class.

What is the usual mode of fertilisation in echinoderms?

Gametes are released into the water column for external fertilisation.

When do most echinoderms reproduce?

Seasonally, often in spring to align with algal blooms.

What is the purpose of seasonal reproduction?

To ensure larvae have access to abundant food.

Do all echinoderm larvae receive parental care?

No, most are left to develop in the plankton.

What is brood protection?

Parental care strategy where offspring are retained and protected to increase survival.

Why is brood protection rare in echinoderms?

It is costly and limits dispersal, but increases survival.

Which classes exhibit brood protection?

Mainly asteroids and ophiuroids, but also echinoids, holothuroids, and crinoids in some cases.

How do asteroids brood their eggs?

Underneath their arched body or in brooding baskets formed by spines.

How do starfish manipulate and oxygenate their eggs?

Using their tube feet.

How do Leptasterias species brood their eggs?

Inside their stomachs, turning off digestive enzymes.

How do ophiuroids protect their young?

In bursae acting as brood pouches.

What is unique about Amphipholus squamata?

It lacks a larval stage; young are born as juveniles.

How do echinoids brood?

They externally carry eggs between spines or near the peristome.

How do holothuroids brood their offspring?

Internally, with juveniles exiting through ruptures in the body wall.

What is viviparity in echinoderms?

Giving birth to live young, seen in some holothuroids.

What is special about Synaptula hydriformis?

It provides nutrients to its young inside the body.

How do crinoids provide brood care?

Eggs are stuck to pinnules or held in internal pouches.

What are the benefits of brood protection?

Higher offspring survival and improved parental fitness.

What are the costs of brooding?

Reduced feeding, lower fecundity, expensive egg production, and less dispersal.