1. Describe pentaradial symmetry and its
applications to the lifestyles of the echinoderms.
2. List five classes within the Phylum Echinodermata
and give examples of each, highlight key differences between each class.
3. Diagram and discuss the echinoderm water
vascular system including its supposed original function and its functions
in living species.
4. Briefly describe the excretory, respiratory
and nervous systems of the echinoderms.
5. Discuss the class Asteroidea, describe the
following aspects of their body plan: ossicles, pedicellaria, spines and
papulae.
6. Diagram a cross section of a sea star showing
the pyloric and cardiac stomachs, gonads, anus, pyloric ceacum, mouth and
coelom.
7. Describe the reproductive capacities and
strategies of the sea star. Also address the sea stars regenerative capabilities
as a reproductive capability.
8. Within the class Echinoidea distinguish between
regular and irregular echinoids.
9. Highlight structural differences and similarities
between the echinoids and the asteroids.
10. Describe the physical characteristics of
the class Holothuroidea.
11. Discuss the unique features of the sea
cucumbers including the respiratory tree, the production of toxins for defense,
cuvarian tubules and eviceration.
12. Discuss the echinoderms relationship to
their environment and the other organisms that they share their habitat with.
13. Describe how a sea star feeds upon a sessile
mollusk.
14. Describe the common characteristic that
the lophophorates posess.
15. Briefly describe the phyla Brachiopoda,
Ectoprocta and Phoronida.
Resources: Text: Animal Diversity, Chapter
14
Internet Resources:
http://www.ucmp.berkeley.edu/echinodermata/echinodermata.html
http://www.calacademy.org/research/izg/echinoderm/
http://www.nmnh.si.edu/gopher~menus/TheEchinodermNewsletter.html
http://www.umassd.edu/Public/People/Kamaral/thesis/SeaStar.html
http://www.mhhe.com/hickmanad4e
Phylum Echinodermata (spiny skin) ~6000 species
Past developments: Bilateral symmetry
---> free moving animals
Radial
symmetry ---> sessile
Echinoderms- freeliving w/radial symmetry;
Pentaradial symmetry as adults
-larva is bilateral, during metamorphosis
90o reorientation w/mouth on left side,
anus on right. Advent of oral and
aboral sides rather than dorsal/ventral
-part of coelom made into water vascular
system unique to echinos
-endoskeleton of plates or fused dermal
ossicles
-pentaradial symmetry- body parts arranged
in fives or multiples of 5
(radial symmetry adaptive for
sedentary or slow moving animals; it allows
even distribution of sensory
and feeding structures)
-respiration by dermal branchiae;
tube feet (diffusion)
-pedicellariae, pinchers that keep body
surface clean
-no excretory organs
PHYLUM ECHINODERMATA
Class Asteroidea- sea stars; rays
(arms) not sharply set off from central disc,
ambulacral grooves w/ tube feet, pedicellaria
present
Class Echinoidea- sea urchins,
sand dollars, globular or disc shaped, no rays,
movable spines, skeleton (test) of
closely fitting plates
Class Holothuroidea- sea cucumbers;
no rays, elongated along oral/aboral axis,
microscopic ossicles embedded in muscular
body, circumoral tentacles
*entirely marine/benthic except for pelagic
larva
*most predaceous on sessile molluscs
*evolution of pentaradial rather than an
even radial arrangement seems to relate to
the strength possessed when weak joints
are not located opposite each other
*no cephalization
*oral/aboral surfaces (not dorsal/ventral)
*organ grade structure
WATER VASCULAR SYSTEM
-compartment of coelom, unique to echinoderms
-original function of WVS was thought to
be food gathering not locomotion
-walls of WVS allow diffusion of respiratory
gases and nitrogenous wastes across
body wall
-consist of a series of water filled canals
and their extensions, tube feet
-water enters through a sievelike plate
called a madreporite
-water travels through stone canal
to ring canal which surrounds mouth
-radial canals branch from ring
canal, associated w/arms
-lateral canals branch off radial
and end at tube feet (podia)
-two rows of tube feet per arm
(one on each side of ambulacral groove), tube
feet extend out through openings in
skeletal ossicles
-each foot internally terminate
in bulblike ampulla. Ampulla contracts to force water
into hollow, muscular tube foot which
then extends. Valves prevent back flow of water
-each tube foot usually possesses
sucker at distal end, foot extends and comes into
contact w/solid surface, muscles of
sucker contract to form vacuum
EXCRETION- diffusion of ammonia/nitrogenous wastes through podia (WVS)
RESPIRATION- general body surface, tube feet, papulae (extensions of coelom)
NERVOUS SYSTEM- simple: nerves, nerve
net (plexus); separate sensory and motor parts;
chemoreception not localized (over
general body surface); ocelli ("eyes")at tip of arm in
seastars
Class Asteroidea- "star"
like ~1600 species
Sea stars, "starfish"; marine, hard and
soft bottom dweller
General Characteristics:
-flattened
-arms not sharply set off from central
disc
-ossicles- embedded in skin,
lattice network (secreted from dermis) heldtogether by
connective tissue
-size variable: more food --->
bigger; less food ---> limits size
-pedicellaria 1. defense
2. kill settling
larva
3. aggression??
-spines- extensions of ossicles
-Papulae (dermal branchiae; skin
gill) project from coelomic cavity, respiratory function
Feeding- 1. Attack whole prey (usually
sessile mollusks)
2. arms exert great
pressure on shells
3. evert cardiac stomach
into shell and wraps around soft insides
4. digestive juices
digest tissues
5. prey into mouth
via cilia on everted stomach
REPRODUCTION/REGENERATION
-dioecious (indistinguishable externally)
-10 gonads (2 in each arm)
-shed gametes into ocean, coordinated
with environmental factors (photoperiod,
temp. . . .); to ensure gametes released
together, release of gametes of one
individual is accompanied by release
of spawning pheromone.
Autonomy- breaking off of parts (injured) from their own body
**powers of regeneration are incredible; new individ from at least 1/5 of central disc.
**Asexual reproduction involves dividing central disc and regeneration
CLASS ECHINOIDEA ~800 species, sea urchins, sand dollars
Regular Echinoids- urchins; spherical,
display pentaradial symmetry
Irregular Echinoids- sand dollars;
flattened, symmetry modified to nearly bilateral form.
Characteristics:
-oral end faces substrate
-plates (10); 5 ambulacral plates (have
openings for tube feet) alternate w/5
interambulacral plates which have
articulations (bumps) for spines
-Spines (defense, locomotion,
burrowing)
*proximal base, concave socket (fits
over articulations); muscles at base for
movement
*sharp, hollow, sometives contain
venom
-pedicellariae 2 or 3 jaws
(defense, prey capture, cleaning)
-WVS similar to other echinoderms
-movement by using spines for pushing
against substrate; tube feet for pulling
(sand dollars use spines for burrowing)
Aristotle's Lantern
-chewing mechanism w/teeth (calcarious
plates)
-cuts food into small pieces for
injestion
-mouth ---> esophagus --->
intestine
Feeding: Regular urchins-
A.L. to bite off algae, encrusting inverts, sediments
Irregular
urchins- deposit feeders, obtain food particles from sand
REPRODUCTION
-dioecious
-5 gonads, located on internal body wall
(during breeding season nearly fill coelom
-sexes impossible to distinguish externally
-fertilization external
CLASS HOLOTHUROIDEA- sea cucumbers ~500 species
-basic pentaradial symmetry
-reduced endoskeleton
-no spines; no pedicellaria
-tubefeet; rows, scattered or absent
-thick body wall, leathery, muscular
Unique features:
1. 2 respiratory trees; branched
tubes that empty into cloaca, water circulates in
these by pumping action of rectum
(both respiratory and excretory)
2. Toxins for defense (some have been found to inhibit growth of cancer cells)
3. Cuvarian tubules- everted
through anus, contain sticky secretions and toxins
capable of entangling and immobilizing
predators
4. Eviceration; expulsion
of respiratory trees, digestive tract; gonads through
anus (some species orally);
defensive to discourage predation. Regenerate
lost parts.