Laboratory 11
Zoology 1121
Phylum Echinodermata
Quiz
Goto WebCt and check out under student materials the dissection slides
and Final Essay Questions
I. General Information on Phylum
1. Over 6000 species found in the sea (marine)
2. Echinoderm – means “spiny skin”
3. Note their position in phylogenetic tree, very advanced
4. Unique with a water-vascular system and endoskeleton
5. First time to see an internal skeleton
6. Deuterostomes – first time we encounter
7. Have weird symmetry pattern that changes based on age of organism:
a. larva – bilateral symmetry
b. adult – radially symmetry
(like the Cnidarians)
8. systems:
1. digestive system – well-developed
2. circulatory system -
not well-developed
3. nervous system – not
well-developed
II. Evolution
1. Echinoderms and Chordates (next week) arise from common ancestor
2. Both bilaterally symmetrical, eucoelomate ancestor
3. Radially symmetrical adult is a “derived” characteristic, one that
emerged due to the selective advantage of radially
symmetry for sessile organisms.
Protostomes vs. Deuterostomes
1. See Campbell for excellent, brief review. Also, we are talking about
Eucoelomates when we use these two terms!
2. Classification based on embryology and on 3 main points
a. Cleavage
1. Pro: spiral and determined
2. Deut: radial and indeterminate
b. Coelom Formation
1. Pro: splits in the mesoderm
2. Deut: invaginations into the mesoderm
c. Mouth Formation
1. Pro: mouth develops first, then anus second
2. Deut: mouth develops second, anus develops first
III. Classification
1. Phylum
a. adult – radially; larva
– bilateral
b. presence of an endoskeleton
(ossicles comprised of calcareous plates)
c. coelomic cavity highly
developed
d. water-vascular system
with tube-feet and madreporite
2. Class Determination
a. Five broad-based arms,
anus on upper surface . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . .C. Asteroida
b. Five slender arms, anus
on bottom . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . .C. Ophiroidea
c. Branched, feathery arms,
mouth and anus on oral surface . . . . . . . . . . . . . . . . .
. . . . . . . . . C. Crinoidea
d. No arms, madreporite
on oral surface on bottom . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . C. Holothuroidea
e. No arms, spherical body,
spines . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . C. Echinoidea
Hint: use presence of arms for narrowing down the classes, then other
criteria
Common names
1. C. Astroidea: sea stars
2. C. Ophiroidea: brittle stars
3. C. Holothuroidea: sea cucumbers
4. C. Crinoidea: feather stars, sea lilies
5. C. Echinoidea: sea urchins
I. Class Astroidea
1. common name are sea stars (i.e., starfish)
2. rocky sea-coast habitat
3. Oral side and aboral side.
4. Aboral side has a madreporite
5. Madreporite – off to the side of the center, which is called a center
disc
6. Body = 5 arms + central disc
7. Anus opens in center disc
8. Has thin epidermis
9. Ossicles are embedded into thin epidermis, ossicles pert of an endoskeleton
10. Ossicles are small calcified plates…do not get this confused with
spicules(P. Porifera)
11. In this particular Class the ossicles have small spies that protrude
through the epiderm.
12. Pedicellariae – ring of little pincers at the base of the skin
spines, although some may be present between the spines
as well.
13. Function of these pedicellariae are to keep skin clean of debris
and other flora/fauna
14. Skin gills – located between the spines [evaginations of the lining
of the body cavity filled with coelomic fluid and
function in gas exchange]
15. Oral side has mouth (remember in this Class the anus is on the
aboral side)
16. Mouth ringed by 5 pairs of small spines
17. Mouth – Cardiac Stomach – Pyloric Stomach - Intestines – Anus
18. This digestive system is arranged vertically in the central disc
19. Ambulacral grooves – spread out down each arm away from the central
disc
20. Tube feet – lines the ambulacral grooves in 4 rows
21. Tube feet also part of the water-vascular system
22. Water-Vascular plan – serves primarily for locomotion and holding
food for feeding
23. This entire system this is filled with seawater.
24. Seawater enters this system through the madreporite, which is a
modified ossicle with many holes (i.e., pores) that act
as filters.
25. Tube feet are hollow and connected to (and part of) the WV system
by both lateral and radial canals
26. Tube feet are connected by bulblike ampullae
Internal Anatomy of Sea Star
1. Has coelomic cavity filled with coelomic fluid (not seawater –which
fills the water-vascular system)
2. This coelom is lined with flagellated mesoderm
3. Digestive System
a. Cardiac stomach fills
most of the central disc
b. Thin walled pyloric stomach
connected directly to the cardiac stomach
c. Five pairs of digestive
glands ring the pyloric stomach & are connected by pyloric ducts.
d. One pair of digestive
gland extends into each of the arms.
e. To differentiate between
the pyloric vs. cardiac stomach follow the digestive glands to the pyloric
ducts to the
pyloric stomach
f. Sea star able to everted
out through the mouth into a clam or oyster in order to feed (its tube
feet are used to
separate the bi-valve)
g. The digestive glands
secrete digestive enzymes into the body of the bivalve and the partially
digested material is
drawn into the stomach for final digestion.
4. Reproduction system
a. Impossible to determine
sex with naked eye, must use microscopy
b. Ventral to the digestive
glands are the two smaller gonads.
c. These organisms are dioecious,
so they house both sexes into two organisms.
d. Gonads are a feathery-looking
collection of tubules with 2 sets per radial arm at the point where the
arm joins
the central disc
e. Gonads connected to outside
world via a genital pore at the junction
f. Thus have external fertilization
5. Nervous System
a. Have a reduced and primitive
nervous system
b. Has nerve ring that surrounds
the mouth and five radial arms
c. Use the cross-section
of the arm to find it (whitish chord)
d. NO cephalization present
in these organisms (why?)
e. Can receive both tactile
and photoreception
f. Nerves enervate the tube
feet as well
6. Skeleton System
a. unusual endoskeleton
b. thin epiderm
c. the dermal cells (underneath
the epidermis) secretes a ossicle made out of calcium carbonate
d. Dermal cells derived
from mesodermal cells not epi- or endo-.
e. continuous yet very flexible
endoskeleton
7. Muscular System
a. Beneath the dermis layer
– very reduced
b. Outer circular and inner
longitudinal
c. One for movement of ambulacral
groove
d. One for each ray (i.e.,
arm)
8. Water-Vascular System
a. stone canal
b. ring canal
c. radial canal
d. lateral canal
e. ampullae and tube feet
II. Class Ophiuroidea
1. common name for brittle stars
2. notice the very slender radial arms
3. arms attached to a flattened central disc
4. Unlike the C. Astroidea, they do not use a WV system for movement.
5. They use arms as “oars” and “row” against the ground very quickly
6. Have no intestine or anus, digestive tract ends in a blind sac (this
is secondary attribute)
7. Also use a small, sac like structure for gas exchange at the central
disc
III. Class Holothuroidea
1. common name sea cucumbers
2. arms are absent
3. weirdly cucumber shaped organisms
4. greatly reduced endoskeleton with microscopic ossicles
5. lacks most other outer epidermal structures as in C. Astroidea
6. tube feet present, some modified into tentacle to feed with
7. madreporite opens directly to coelom but NOT into the environment
8. long, coiled intestine that terminates to anus
9. have respiratory trees for gas exchange which are evaginations off
the digestive system
IV. Class Crinoidea
1. common name feather stars and sea lilies
2. oldest and most primitive of Phylum, a lot found in fossil evidence
3. these are sessile
4. highly branched and folded arms
5. arms feathery in appearance
6. up to 200 arms, unlike five C. Astroidea
7. have pinnules which are small branches off the main arms
8. pinnules are unique to the class
9. pinnules use mucus secretion to trap food and then travels down
in a bolus (i.e., a ball) down the ambulacral grooves
to mouth
V. Class Echinoidea
1. common name sea urchins
2. no arms present
3. tube feet arranged in rows
4. ambulacral groove located between the rows, with ambulacral plates
5. have a mouth on oral side that is surrounded by a round lip and
five pairs of oral tube feet
6. Also has five teeth under round lip (Called Aristotle’s lantern)
7. Highly branched gills
8. Ball-and-socket joints attach the spines to the fussed ossicles
9. Small madreporite on aboral side
10. Genital pore on aboral too
11. External fertilization
VI. Embryology
1. big name for “animal development” dealing with how an organism develops
from fertilization onward
2. Fertilization occurs when:
a. egg and sperm meet
b. entry of sperm into egg
c. fusion of egg and sperm
pronuclei (i.e., each’s haploid DNA)
d. activation of synthesis
mechanisms
e. successive divisions
of the new cell ala mitosis
1. remember, meiosis is the creation of sex cells – diploid to haploid
VII. Lab Experiment
1. Discuss the organisms that can undergo asexual as well as sexual
reproduction.
2. Discuss again the advantages and disadvantages of undergoing either
type of reproduction.
3. Discuss external fertilization and the advantages and disadvantages
associated with this type of fertilization.
4. Understand the importance of this group in developmental research.
Explain why we study development with this group. For example,
sea urchins are Deuterostomes (like the chordates) and show similar developmental
patterns; for this reason, they have been incorporated into the study of
mechanisms involved in embryonic development.
1. Embyology Continued
1. study of how an animal devolops from fertilization
2. impossible to tell sex of sea urchin so add KCL to its mouth and
see what gametes come out
3. if gametes are red then female, if gametes are whute then male
4. We will look at unfertilized female eggs under microscope
5. Then add sperm from male
6. Find ones going through fertilization
7. Look for fertilization membrane around newly fertilized eggs
8. Why there? To block out other competing sperm so there is only one
fertilizes egg.
9. The process of sea star:
a. fertilized zygote – 1
cell stage
b. first second stage cleavage
c. Morula – after a few
more rounds of cleavage [morula = Latin for raspberry]
d. Blastula with Blastocoel
e. Gastrula
f. Archenteron
g. Bipinnaria larva (note
its bilateral symmetry)
10. The stages:
a. Fertilization
b. Morulation
c. Blastulation
d. Gastrulation
e. Neurolation
11. Mnemonic: create a sentence for this –
F
M B G
N
12. Record time it takes for each stage.
IMPORTANT TERMS:
Echinodermata
Radially symmetrical adult
Bilaterally symmetrical larvae
Water vascular system
Endoskeleton
Spines
Pedicellareae
Madreporite
Arm
Central disc
Eye spot
Ambulacral groove
Ossicle
Anus
Intestine
Intestinal cecum
Pyloric stomach
Pyloric duct
Digestive gland
Cardiac stomach
Mouth
Stone canal
Ring canal
Radial canal
Lateral canal
Ampulla
Tube feet
Coelomic cavity
Gonad
Unfertilized egg
Fertilized egg
Fertilization membrane
Cleavage (early - late)
Blastula,
Blastocoel
Gastrulation
Gastrula
Archenteron
Endoderm
Mesoderm
Ectoderm
Deuterostomes
Protostomes
Larvae
Differentiation