Echinoderms“Life with Spiny Skin”

Worms, mollusks, and arthropods all have bilateral symmetry.

So do echinoderm larvae.

What kind of symmetry do adult echinoderms have?

Radial symmetryWhat other animal

phyla display radial

symmetry?

A Radical Radial Change

Bipinnaria larvae (sea star)

Five Alive

Most echinoderms show pentamerous radial symmetry.

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

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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. The

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

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

aboral

oral

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

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.

Ophiothrix spiculata

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.

oral

aboral

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.

Holothuroidea Defense

Secrete toxins Discharge

sticky toxic filaments

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

Sea cucumber evisceration

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