L18 Echinoderms

What are the most important characteristics of echinoderms?

Calcerous skeleton

Water vascular system

Pentaradial (five-fold) symmetry in adults

In echinoderms what is the endoskeleton made of?

Dermal calcareous ossicles with spines

Calcareous spicules in dermis (sterom)

What is the epidermis covered by in echinoderms?

Epidermis (ciliated in most)

Pedicellariae (in some)

Where does water enter in the water vascular system?

Madreporite

After water has endered the madreporite what happens next?

It is pushed through fluid-filled canals connecting tube feet

What the water vasular system used for?

Locomotion, food and respiration

Exact structures vary between classes

What body shape do echinoderms have?

Rounded

Cylindracal

Star-shapd

What are ambulacra and what are there function?

Radial bands on the surface of echinoderms
Give rise to tube feet

What is the function of ampulla?

Ampulla holds water, when water leaves the foot can inflate

Radial canal function

Act as hydrolic channels

Characteristics of echinoderms body?

Unsegmented with pentaradial symmetry, no head, ambulacra and interambulacral areas

What symmetry did ancestor of echinoderm have?

Bilateral

Four main classes of echinoderms:

Asteriods (star fish)

Ophiuroids (brittle stars)

Holothurians (sea cucumbers)

Echinoids (sea urchins)

Define synapomorphy:

Shared, evolutionary derived characters indicating common descent

Where do asteroidea live?

Shorelines and may aggregate on rocks

Muddy or sandy bottoms

Coral reefs

Class asteroidea have an effect on the whole ecosystem what does this mean?

They are keystone species

What is the body plan of class asterodiea (sea stars)

Central disc with tapering arms extending outward

Where is the mouth located in class asteroidea?

Underside or oral surface

In class asteroidea what is the opposite of the oral surface called?

Aboral surface

How many arms do sea stars have (asteroidea)?

5 but could be more

What is the ambulacral groove borded by?

rows of tube feet

Function of pedicellariae:

Appendages used for defense

What are the two types of pedicellariae present in class asterodiea?

Large forcep pedicellaria: Protection

Small forcep pedicellaria: Cleaning

What are papulae?

Soft projections lined with peritoneum - function in respiration by increasing surface for gas exchange

What class of echinoderms have the largest number of species?

Ophiurodiea - Brittle stars

Explain the arms of brittle stars

Slender and distinct from the central disc

What does class ophiuroidea lack?

Pedicellariae and papulae

Tube feet lack suckers

Anus

What are tube feet used for in class ophiuroidea?

Feeding

Orinetation

Not locomotion

What do brittle stars use for locomotion?

Long, flexible arms

In brittle stars where are madreporite?

Oral surface

What does class Echinoidea lack?

Arms

Even though class Echinoidea lack arms what do they still have?

Five part symmetry

What shape do ‘regular’ sea urchins have?

hemispherical with radial symmetry and long spines

What are irregular sea urchins?

Sand dollars

Secondary bilateral

Short spines

How do echinoids move?

Tube feet and/or spines

What class of echinoderms have pedicellariae that carry venom?

Echinoidea

How do class Echinodea move?

Use flexible tube feet

Explain what role spines and tube play in locomotion in echinoidea:

Tube feet assisted by the spines, used for pushing the body along or to lift off the substrate

What are the characteristics of class echinoidea?

Anus

Genital pores

Madreporite are abrol

Pedicelariae have jaws and bear venom in many species

5 converging teeth surround the mouth

Describe the body type of class holothuroidea:

Greatly elongated in the oral-aboral axis but still pentaradial

Cephalisation is absent

Function of ossicles:

Scatered throughout dermal layer and provide protection by making the skin to tough for predators to eat

Describe ossicles in class holothuroidea:

Greatly reduced and body wall is leathery

Where do holothuroids live?

Crawl on the bottom of the ocean

Under rocks

Under burrows

What are the threats to echinoderms?

Souveniers

Urchins as food

Cucumbers as food

Sea stars

Mostly predators Asteroids

Brittle stars

May be scavengers or commensal with sponges Ophiuroids

Sea cucumers

Mostly suspension or deposit feeders Holothurians

Sea urchins

Feed on detritus or algae Echinoids