Echinodermata

Marine Biology
Field Guide
Table of Contents
All Life
Prokaryotes
Domain
Eubacteria
Kingdom
Monera
Eukaryotes
Domain
Archaea
Domain
Eukaryota
Kingdom
Fungi
Kingdom
Protista
Kingdom
Plantae
Kingdom
Animalia
Kingdom Animalia
• Multicellular / Eukaryotic
• Sexual reproduction
• Life cycle:
- adult always diploid
- embryo undergoes stages of development
• Heterotrophic - most ingest, then digest
• Most motile by muscle fiber
• Grouped into about 30 phyla
Some major phyla of animalia
1) Chordata (chordates)
2) Echinodermata (echinoderms)
3) Arthoropoda (arthropods)
4) Mollusca (molluscs)
5) Brachiopoda ( lamp shells)
6) Phoronida (phoronids)
7) Bryozoa (bryozoans)
8) Annelida (segmented worms)
9) Nematoda (roundworms)
10) Nemetera (ribbon worms)
11) Platyhelminthes (flatworms)
12) Ctenophora (comb jellies)
13) Cnidaria or Coelenterata (cnidarians or coelenterates)
14) Porifera (sponges)
Animalia (invertebrates)
Phylum
Echinodermata
Class
Holothuroidea
Class
Echinoidea
Class
Stelleroidea
Echinodermata – the echinoderms
• Approximately 7,000 species
• Have spiny skin.
• Radially symmetrical as adults. Larvae are bilaterally symmetrical.
• Pentamerous radial symmetry.
• Body has no dorsal, ventral, anterior, or posterior side, instead one
surface is referred to as the oral (mouth) side and the other is the aboral
side.
• Three main classes: Holothuroidea, Echinoidea, and Stelleroidea
(Asteroidea).
Class Holothuroidea
• Approximately 1400 species.
• Sea Cucumbers
• Worm-like in shape.
• Skin can be smooth or warty.
• Skin imbedded calcareous deposits.
• Some ingest bottom material.
• Others trap plankton or sweep up detritus with their tentacles.
• Can expel most of their internal organs to confuse predators.
• Bodies can contain toxins that can deter attackers.
Hairy Sea Cucumber
Sclerodactyla briareus
Hairy Sea Cucumber
Sclerodactyla briareus
Hairy Sea Cucumber
Sclerodactyla briareus
Hairy Sea Cucumber
Sclerodactyla briareus
Hairy Sea Cucumber
Sclerodactyla briareus
Description: Its body is about 4 ¾ long, 2 inches wide, and resembles the shape of a sweet
potato. It looks a little like a hairy stone. Its surface can range in color from black and brown,
to green or purplish. Their bodies are thickest in the middle; the mouth and anal ends are
curved upward and are covered with fine tubular feet. The sea cucumber also has 10 large,
branchlike tentacles around its mouth.
Habitat: The Hairy Sea Cucumber uses its tube feet to creep along the substrate or to build up a
“volcano-like” formation of sediment around itself. When buried it leaves only its mouth and
anal opening exposed.
Range: The hairy cucumber is a common holothuroid that occurs in shallow waters along the
east coast of North America from Massachusetts and south to Florida and the Gulf of Mexico.
Sea Cucumbers are found in higher salinity waters, on muddy or sandy bottoms, from the lowtide line to 20 feet deep.
Comments: The tentacles sweep food particles into the mouth and can be retracted into their
body. If a sea cucumber is picked up or otherwise disturbed, it will (like a sea squirt) expel
water from the rear opening, and if the disturbance is intense it can even expel some of their
internal parts, which may sometimes—not always—results in the death of the animal.
Generalized Sea Cucumber Anatomy
The body of the sea cucumber is elongated, leathery and muscular; spines are
contained within the skin. These echinoderms have no arms, but do have fivepart symmetry. Surrounding the mouth are 8 to 30 tentacles (modified tube
feet). Five double rows of tube feet (with tiny suction cups) run along the
body; they are used for crawling along the sea bed or anchoring to a rock. A
sea cucumber breathes by pumping sea water in and out of an internal organ
called a respiratory tree.
Class Echinoidea
• Sea Urchins and Sand Dollars
• Skeleton consists of calcareous plates fit together in a rigid outer
covering.
• Body is covered in fine to coarse movable spines.
Generalized Sand Dollar Anatomy
Sand Dollar
Echinarachnius parma
Sand Dollar
Echinarachnius parma
Sand Dollar
Echinarachnius parma
Description: This animal lacks the five arms that are characteristic of the phylum but
does possess the same five-part radial symmetry (Raven and Johnson 1999). It is
generally about 5-10cm in diameter when fully grown. They have spines on the
somewhat flattened underside of the animal allow it to burrow or to slowly creep
through the sand. Fine, hair-like cilia cover the tiny spines. These cilia, in combination
with a mucous coating, move food to the mouth opening which is in the center of the
star shaped grooves on the underside of the animal (Page 2000). The opening for the
anus is opposite the mouth on the aboral surface.
Habitat: Sand dollars are found in the intertidal zones and a little deeper. Often their
skeletons will wash ashore after a storm. They burrow into the sand for protection and
for food (Banister and Campbell 1985).
Range: This species is the common sand dollar of the North American east coast from
New Jersey north. It is circumpolar and also occurs in Alaska, British Columbia,
Siberia and Japan (Fox 1997).
Sand Dollar
Echinarachnius parma
Comments: The sand dollar burrows in the sand at the sea bottom
feeding on algae and fragments of organic material found in there.
They scrape off substrate with large, triangular teeth that ring their
mouth. The teeth visible in the center of the mouth are continually
growing while being worn away at their free ends. Therefore, although
they are held firmly in place by ligaments and other ossicles of the
jaws, the teeth must be periodically shifted toward the mouth. This
shifting is apparently accomplished by tiny muscles (Telford & Ellers
1997). The tube feet aid in moving substrate to the mouth. Sand
dollars generally feed on the detritus found in the filtered substrate, but
they will also feed on small plankton and algae (Grzimek 1972).
Generalized
Sea Urchin
Anatomy
mouth
Purple-Spined Sea Urchin
Arbacia punctulata
Purple-Spined Sea Urchin
Arbacia punctulata
Purple-Spined Sea Urchin
Arbacia punctulata
Purple-Spined Sea Urchin
Arbacia punctulata
Description: The Arbacia punctulata has a deep purple color all over the spines and body
(test). Their body area, called a test, can grow to a diameter of 3-5 cm. In addition, they are
radially symmetrical.
Habitat: These purple sea urchins are found most commonly on rocks and shells in somewhat
deep salt water. They prefer to live on rocks or shell bottoms from the low-tide line to a water
depth of about 750 feet (229 meters).
Range: Arbacia punctulata is a common urchin from Cape Cod to the West Indies.
Comments: Purple sea urchins, like all sea urchins, are the porcupines of the sea. They have
long spines in order to deter predators. Even the name, Sea Urchin, comes from the Old
English term for spiny hedgehog. This test is made up of ten fused plates that encircle the
urchin. Each of these fused plates has small holes from which the feet extend. These feet are
controlled by an internal water vascular system. This system works by varying the amount of
water inside which regulates if the feet are extended or contracted. Sea urchins also have a
unique structure called Aristotle's lantern. This structure is made of five hard plates that move
together like a beak. They use this beak like structure to scrape rocks clean of algae. These
'teeth' can also grow back after too much wear. They have a mouth at the underside and an
anus at the top of the animal.
Class Stelleroidea (Asteroidea)
Sea Stars and Brittle Stars
• Most have 5 arms that radiate from a central disk.
• Each arm has a channel that runs its length called the ambulacral
groove.
• Ambulacral grooves have hundreds of tube feet.
Generalized external anatomy of Stelleroidea
Aboral side
Oral side
Generalized internal anatomy of an Echinoderm
Water vascular system = Forces water around the body using muscular action
(a hydraulic system), is unique to the group and is
used in respiration, locomotion, and feeding.
Margined Sea Star
Astropecten americanus
Margined Sea Star
Astropecten americanus
Margined Sea Star
Astropecten americanus
Description: These are handsome sea stars with distinct upper and lower marginal plates.
Upper plates without continuous spines; lower plates with a fringe of spines. Upper side
covered with paxillae. Radius is 3-5 inches.
Habitat: They live on bottoms ranging from coarse gravel to fine mud, although they usually
live on sand. Sand stars live partially or completely buried. They travel into deeper water
during the winter and swarm closer to shore when the seawater warms between May and July.
They then release their eggs and sperm into the water, where fertilization takes place.
Range: Common on the East Coast of the United States from New Jersey to Cape Hatteras.
Found from the low tide line to 150 ft.
Comments: Sand stars are greedy predators of mollusks, worms, crustaceans, and other sea
stars and their relatives. They dig up their prey and swallow it whole. Starfish are well known
for their powers of regeneration. A complete new animal can grow from a small fragment such
as a arm. In some species (Linckia multifora and Echinaster luzonicus) one of the arms will
virtually pull itself away, regenerates and forms a new animal. Autotomy (self amputation)
usually is a protective function, losing the body part to escape a predator rather than being
eaten. But here it serves as a form of asexual reproduction. In other species of sea stars
(Allostichaster polyplax and Coscinasterias calamaria) the body is broken into unequal parts (=
fission) then the missing limbs regenerate.
The madreporite structure
This structure will be found on the
top, or aboral (away from the
mouth) surface, of most sea stars.
It is usually about 1/50th of the
diameter of the sea star’s arms, so
it can be easily missed. When 18th
century biologists studied sea stars
closely with a microscope, they
thought this structure looked like a
miniature brain coral. Brain corals belong to a group called the madreporarian
corals, so the name of this sea star structure became the madreporite. Sea
water can pass through the madreporite and enter the animal’s water vascular
system. The madreporite acts as an effective filter, keeping out floating particles
and living organisms (such as parasites) that might harm the sea star.
Forbes' Asterias
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