notes Echinoderms

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Echinoderms

“Life with Spiny Skin”

A Radical Radial Change

Worms, mollusks, and arthropods all have bilateral symmetry.

So do echinoderm larvae.

What kind of symmetry do adult echinoderms have?

Radial symmetry

What other animal phyla display radial symmetry?

Bipinnaria larvae (sea star)

5

1

Five Alive

4

2

3

Most echinoderms show pentamerous radial symmetry.

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

Spiny Skin – but only the skin!

Echinoderm means “ spiny skin .”

Echinoderms typically have:

 well developed digestive tracts

 well-developed coelom

Internal skeleton called an endoskeleton

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

What No Top and Bottom?

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

Rather than use the term dorsal, the side of the echinoderm without a mouth is called the aboral side.

aboral oral

The echinoderm mouth is usually on the bottom. This is termed the oral side.

Water vascular system

A network of water-filled canals that function in movement, feeding, and excretion.

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

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

Water Vascular System

Water Vascular System

Types of Echinoderms

Approximately 7,000 species – all marine

Located from the poles to the tropics

Five major classes

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

Ophiuroidea (brittle stars)

Echinoidea (sea urchins and sand dollars)

Holothuroidea (sea cucumbers) – not a vegetable!

Crinoidea (feather stars and sea lilies)

Asteroidea

Endoskeleton rather flexible to allow for movement.

Most have five arms radiating from a central disk.

Asteroidea

Hundreds of tube feet are found in channels called ambulacral grooves radiating from the central disk.

Asteroidea

Naturally the anus is on the aboral (top) side.

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

Asteroidea

Ophiothrix spiculata

Ophiuroidea

Brittle stars

Most numerous class of echinoderms.

Characterized by thin, very flexible arms.

Eat particulate matter on the ocean floor.

No anus.

Often hidden.

Ophiuroidea

Echinoidea

Sea urchins & sand dollars

Endoskeleton is a rigid, shell-like “ test .”

Covered with movable spines – used in locomotion and defense.

Grazers – feed on algae and dead organic matter.

aboral oral

Echinoidea

An intricate mouth and jaw system called the Aristotle’s lantern consists of 50 bones and is controlled by over 60 muscles.

Echinoidea

Not all “urchins” have prominent spines.

Sand dollars have flattened bodies and tiny spines.

They use a mixture of mucus and physics to capture food.

Holothuroidea

Sea cucumbers

Elongated version of the pentamerous body plan.

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

Tough skin supported by calcareous spicules.

Holothuroidea

Tube feet near the mouth are modified into tentacles for feeding.

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

Sea cucumber evisceration

Holothuroidea

Defense

Secrete toxins

Discharge sticky toxic filaments

Eviscerate – eject a portion of the internal organs to confuse an attacker.

Crinoidea

Feather stars, basket stars, sea lilies

Suspension feeders

Oral surface on top

Can have from 5 to 200 arms!

Have claw like appendages that hold the aboral surface to the substrate.

Crinoidea

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