Download Biol 212 Zoology Lab 10: Phylum Echinodermata

Biol 212 Zoology
Lab 10: Phylum Echinodermata (10 points)
Introduction
Members of the phylum Echinodermata include
the starfish (sea stars, if you prefer), sea urchins, brittle
stars, sea cucumbers, sea lilies and other related groups.
There are about 6000 living species described, all of
which are marine and benthic.
Echinoderms have a dermal endoskeleton
consisting of calcareous ossicles covered by epidermis,
except where the epidermis has been abraded away (Figs.
10.3 and 10.4). Ossicles usually form flattened,
interlocking plates, or may form spines; thus, the phyletic
name, “Echinodermata,” which means, “spiny skin.”
Ossicles are on apomorphic (unique, definitive)
characteristic of this phylum.
Fig. 10.1: Class Asteroidea,
Pedicillaria are found in some classes of
Pisaster ochraceus, showing radial
echinoderms (Fig. 10.3). These structures, derived from
pentameric symmetry. Rule = 4 cm.
ossicles, are pincer-like devices that seize and remove
from the integument debris and organisms that attempt to
attach. Some starfish pedicillaria are so large, in fact, that they may be used to grab small fish
that rest atop the starfish, killing the fish and making it available for food for the echinoderm!
Pedicillaria are a second apomorphic
characteristic of this phylum.
A third apomorphic characteristic
of echinoderms is the secondarily-derived
radial symmetry, found in adults.
Although echinoderm larvae are bilateral
(Fig. 10.5), they become radial after
settling out of the plankton onto the sea
floor or onto other substrates. Since most,
but not all, adult echinoderms have five
repeated body segments, we say they have
a radial pentameric symmetry. For
example, each of the five arms of a
starfish is a body segment, each complete
with its own pair of digestive diverticula
(pyloric caeca) and gonads (see Figs. 10.1
and 10.3).
Fig. 10.2: Class Asteroidea, water
A fourth apomorphic characteristic of
vascular system.
echinoderms is their water vascular system
(Fig. 10.2). On the aboral (top) surface of an echinoderm is the madreporite; it is a large,
obvious structure with tiny holes in it located laterally to the center point of the starfish. The
Putman/Pierce College Biol 212 Lab 10/20160422/Page 1
madreporite apparently serves as a
pressure release valve for the water
vascular system. The madreporite
is connected to the stone canal,
which connects to the ring canal.
Radial canals extend into each
arm from the ring canal. Lateral
canals extend from the radial
canals and attach to the tube feet,
which protrude from the body in
the ambulacral grooves, found on
the oral surface in the starfish (Fig.
10.3). The entire water vascular
system is closed to the
environment and is full of fluid
absorbed from the coelom, the
body cavity of the animal. Each
tube foot is connected to a sac-like
ampulla that serves to store fluid.
The tube feet and ampullae both
Fig. 10.3: Class Asteroidea, cross
have muscles that regulate the amount of
section of arm.
fluid within the tube feet. This regulation of
fluid allows the tube feet to bend, extend and
contract with very little energy expenditure; thus, a starfish can clamp onto a mussel or other
bivalve mollusk, attach its tube feet onto the shell, then remove the fluid from the tube feet,
creating powerful
hydraulic pressure.
The bivalve must use
constant contraction of
its adductor muscles to
keep its shell closed;
in the end, the
effortless hydraulic
pressure exerted by the
starfish allows it to
open the shell and
consume the bivalve.
Echinoderms
are deuterostomes, that
is, during gastrulation
in embryonic
development, the anus
Fig. 10.3: Class Asteroidea, transverse section of arm.
forms first, the mouth last. They
are enterocoelomates, having a true
coelomic cavity, an enterocoel (the perivisceral coelom in Fig. 10.4), derived from pouches of
the primitive gut; thus, the coelomic cavity, which is the spacious body cavity seen in adults, is
Putman/Pierce College Biol 212 Lab 10/20160422/Page 2
completely lined with peritoneum. In early development, cleavage is radial, unlike the spiral
cleavage seen in protostomes. These developmental characteristics are also seen in the phylum
Chordata (and the phylum Hemichordata), making echinoderms very early relatives of the
chordates, including humans; this relationship is unambiguously supported by molecular
phylogenetics as well.
Using a starfish as a representative echinoderm, the digestive system begins with the
mouth, located on the oral surface (underside) of the animal (Fig. 10.4). The mouth of some
echinoderms may contain an elaborate jaw apparatus, such as the Aristotle’s lantern structure of
echinoids (sea urchins, class Echinoidea) that is capable of nipping away at the holdfasts of giant
kelp, or grinding coral into sand. A short esophagus conveys food into the cardiac stomach. In
some starfish, the cardiac stomach is eversible, the animal capable of protruding it out of the
body in order to digest food in situ. For instance, some starfish that feed on mussels and clams
need to open the bivalve shell only a little; they can then evert their stomach into the bivalve and
digest it from the inside! Crown-of-thorns starfish, which eat corals, evert their stomach onto the
corals and digest the coral polyps where they live. The cardiac stomach then transfers food to the
smaller pyloric stomach. The pyloric stomach sends out paired extensions into the arms called
pyloric caeca, which are located dorsally, dorsal to the paired gonads. The pyloric caeca produce
digestive enzymes, digest the food and absorb the digested nutrients. A short intestine then
conveys the undigested food to the anus, located on the aboral surface.
There is a bit of circulatory system in echinoderms called the hemal system, but no
pumping structure, no heart; in fact, the water vascular system and movement of fluid in the
coelom provide much of the internal transport that a circulatory system would provide. The
hemal system consists of an oral ring that surrounds the mouth and sends tubules into the
gonads; an aboral ring that surrounds the anus and sends extensions into the pyloric caeca; and
tubules that connect the oral and aboral ring, located very close to the stone canal. The hemal
system is very difficult to see in all but the most careful of dissections.
Respiration and excretion in echinoderms is generally carried out through the skin.
Extensions of the epidermis and peritoneum called papulae protrude out from between the
ossicles of the skeleton (Fig. 10.4). These extensions contain coelomic fluid directly from and
connected to the body cavity. Oxygen can diffuse in through the epidermis/peritoneum
membrane into the coelomic fluid, and carbon dioxide and nitrogenous wastes can diffuse out
from the coelomic fluid into the environment. Holothuroids (sea cucumbers) have internal
branches of the rectum called the respiratory tree; they are capable of bringing water with
dissolved oxygen in through the anus to fill the respiratory tree, then expel water the same way,
along with carbon dioxide and nitrogenous wastes.
The echinoderm nervous system is in two parts, one mostly sensory, one mostly motor.
The mostly sensory system consists of a circumenteric nerve ring around the mouth with
radial nerves extending to either side of the ambulacral groove, connecting to nerves that run to
the tube feet and eye spot, which is located at the end of each arm. The mostly motor system,
which is connected to the mostly sensory system, forms a nerve net within the body wall,
internal to the peritoneum.
Each arm of a sexually-mature asteroid starfish has a pair of gonads, located ventrally to
either side of the ambulacral groove, under the dorsally-located pyloric caeca. Echinoderms are
generally gonochoristic (dioecious), having separate male and female individuals, although they
do not exhibit sexual dimorphism. They reproduce by expelling gametes into the water column
through gonopores located on the aboral surface of the animal (Fig. 10.3). Sperm fertilizes the
Putman/Pierce College Biol 212 Lab 10/20160422/Page 3
ova, the resultant zygotes develop into various larval types
unique to the Echinodermata, but all with the general structure
shown in Fig. 10.5. A few echinoderms brood their young.
There are six living classes of echinoderms, five of which
we will look at in this lab. A summary of the echinoderm classes,
with common names, is as follows:
Phylum Echinodermata
Class Asteroidea (starfish, sea stars)
Class Ophiuroidea (brittle stars, basket stars)
Class Echinoidea (sea urchins, sand dollars)
Class Holothuroidea (sea cucumbers)
Class Crinoidea (sea lilies)
Class Concentricycloidea (sea daisys)
Fig. 10.5: Bipinnaria larva,
characteristic of the class
Asteroidea. Rule = 100 m.
The sixth class, class Concentricycloidea, is a deep-sea group represented by only two species;
you’d need a submarine to collect them!
The purpose of this lab is to introduce you to the anatomy of a typical echinoderm, the
starfish, and to familiarize you with the general characteristics of the five major echinoderm
classes.
For the Lab Report:
*On the upper, right-hand corner of your lab report, print your name, Biol 212, Lab 10: Phylum
Echinodermata, and the date you did this lab.
Introductory Objectives
Objective 1: State why echinoderms are called echinoderms.
Objective 2: Explain four apomorphic characteristics distinguishing echinoderms from other
animal phyla.
Objective 3: Describe the structure of the echinoderm water vascular system.
Objective 4: Describe the structure of the echinoderm digestive system.
Objective 5: Discuss three ways in which internal body fluids are circulated in echinoderms.
Objective 6: State how respiration and excretion are carried out in most echinoderms.
Objective 7: Describe the nervous system of echinoderms
Objective 8: Give the location and numbers of gonads in starfish.
Objective 9: State whether echinoderms are gonochoristic or hermaphroditic.
For the Lab Report:
Write out these questions then answer them:
1. Why are echinoderms called echinoderms?
2. List and explain four apomorphic characteristics distinguishing echinoderms from other
animal phyla
Putman/Pierce College Biol 212 Lab 10/20160422/Page 4
For the Lab Report:
Write out these questions then answer them:
3. Describe the structure of the echinoderm water vascular system.
4. Describe the structure of the echinoderm digestive system.
5. Explain three ways in which internal body fluids are circulated in echinoderms.
6. How is respiration and excretion carried out in most echinoderms?
7. Describe the nervouys system of echinoderms.
8. How many gonads do most echinoderms have and where are the gonads located in starfish?
9. Are echinoderms gonochoristic or hermaphroditic?
Exercise 10.1: Class Asteroidea
Introduction
There are over 1500 living species of asteroids, animals commonly called “starfish” or
“sea stars.” Asteroids have five (or more) arms, not clearly separated from the central disc as in
the ophiuroids (compare Figs. 10.1 to 10.6). The anus and madreporite are on the aboral surface,
mouth on the oral surface. The ambulacral grooves are open and contain tube feet.
Objectives
Objective 10: Identify the following structures on a specimen or photograph of an asteroid:
aboral surface, rays (arms), madreporite, anus, spines, ossicles, pedicillaria, dermal branchiae
(dermal papulae), eye spots, oral surface, mouth, tube feet and ambulacral groove.
Objective 11: Identify the following internal structures on a dissected specimen or photograph of
an asteroid: coelomic cavity, anus, intestine, rectal ceca, pyloric stomach, pyloric ceca, cardiac
stoma, mouth, coelomic cavity, gonads, gonoducts, madreporite, stone canal, ring canal, radial
canal, lateral canas and ampullae of the tube feet.
Objective 12: From specimens or photographs, give the phylum, class, species and common
names of typical representatives of the echinoderm class Asteroidea. Learn any species names
assigned by your instructor.
Materials and Methods
*Preserved (deossified) starfish (Asteroidea) for dissection
-Dissection pans
-Dissection tools (needle probes, maul probes, forceps, blunt scissors, scalpels or straight-edged
razor blades)
-Dissecting microscope
*Plastomount or dried representatives of class Asteroidea (demo)
1. Obtain a dissection pan and dissecting tools to include a pair of blunt scissors; do not use the
fine-tipped scissors for this dissection! Also obtain a dissecting microscope.
Putman/Pierce College Biol 212 Lab 10/20160422/Page 5
2. Obtain a preserved starfish; note that this starfish has been treated with acid to deossify it,
making it easier to dissect.
3. Identify the aboral (dorsal) surface. Draw and label the starfish as per the For the Lab Report
box below.
For the Lab Report:
10. Write out, “10. Phylum Echinodermata, class Asteroidea, Genus species [if known], aboral
surface.” Draw the aboral surface of a starfish. Identify and label the rays (arms),
madreporite, anus and spines. Include an accurate size rule next to your drawing. No credit
for drawings without accurate size rules. To the right of your drawing, state how big the size
rule is. Also, include any notes that might help you to identify the organism on the lab
practical! Have your instructor check and initial your drawings for credit; all drawings must
be completed in lab and signed by your instructor for credit!
4. Using a dissecting microscope, focus in on the central disc—you may have to remove a ray
to do this! With a scalpel or single-edged razor blade, cut one of the rays off near the central
disc; save it for later. Draw and label what you see on the central disc as per the For the Lab
Report box below.
For the Lab Report:
11. Write out, “11. Phylum Echinodermata, class Asteroidea, Genus species [if known], central
disc.” Draw the central disc area. Identify and label the madreporite, spines, pedicillaria and
dermal branchiae (dermal pupilae). Include an accurate size rule next to your drawing. No
credit for drawings without accurate size rules. To the right of your drawing, state how big
the size rule is. Also, include any notes that might help you to identify the organism on the
lab practical! Have your instructor check and initial your drawings for credit; all drawings
must be completed in lab and signed by your instructor for credit!
5. Cut off the end of one of the arms about 1 cm from the end. Examine it under the dissecting
microscope. Increase the magnification to maximum and examine the tip. Find an eyespot
(purple dot). Draw and label it as per the For the Lab Report box below.
For the Lab Report:
12. Write out, “12. Phylum Echinodermata, class Asteroidea, Genus species [if known], eye
spot.” Draw an eyespot (purpole spot) at the end of one of the arms. Include an accurate size
rule next to your drawing. No credit for drawings without accurate size rules. To the right of
your drawing, state how big the size rule is. Also, include any notes that might help you to
identify the organism on the lab practical! Have your instructor check and initial your
drawings for credit; all drawings must be completed in lab and signed by your instructor for
credit!
Putman/Pierce College Biol 212 Lab 10/20160422/Page 6
6. Turn the starfish over. Draw the oral surface, including the mouth, tube feet and ambulacral
groove, and label it as per the For the Lab Report box below.
For the Lab Report:
13. Write out, “13. Phylum Echinodermata, class Asteroidea, Genus species [if known], aboral
surface.” Draw the aboral surface and label the mouth, tube feet and ambulacral groove.
Include an accurate size rule next to your drawing. No credit for drawings without accurate
size rules. To the right of your drawing, state how big the size rule is. Also, include any notes
that might help you to identify the organism on the lab practical! Have your instructor check
and initial your drawings for credit; all drawings must be completed in lab and signed by
your instructor for credit!
7. Beginning at the end of the arm with the cut-off tip, using heavy, blunt-end scissors (DO
NOT USE FINE-POINT SCISSORS FOR THIS!), cut into the open edge of the starfish on
the lateral side up toward the central disc; cut the arm on the other side as well. Then cut the
edge of the central disc all the way around, finally making a cut around the madreporite. The
idea here is to remove the dorsal (aboral) surface of the arm and central disc from the animal
to view the underlying structures—you make a cut around the madreporite to allow it to stay
in place as it is connected to the stone canal beneath. Be sure to keep your dissection moist,
by occasionally squirting water on it, to observe internal structures better. Draw and label
your dissection as per the For the Lab Report box below.
For the Lab Report:
14. Write out, “14. Phylum Echinodermata, class Asteroidea, Genus species [if known], internal
anatomy.” Draw your dissection. Locate, draw and label the anus, intestine, rectal ceca,
pyloric stomach, pyloric ceca, cardiac stomach, mouth, gonads and coelomic cavity. No
credit for drawings without accurate size rules. To the right of your drawing, state how big
the size rule is. Also, include any notes that might help you to identify the organism on the
lab practical! Have your instructor check and initial your drawings for credit; all drawings
must be completed in lab and signed by your instructor for credit!
8. Carefully remove the tissues overlying the water vascular system in the central disc and in
the exposed arm. Draw and label your dissection as per the For the Lab Report box below.
For the Lab Report:
15. Write out, “15. Phylum Echinodermata, class Asteroidea, Genus species [if known], water
vascular system.” Draw your dissection. Locate, draw and label the madreporite, stone canal,
ring canal, radial canal, lateral canals and ampullae of the tube feet. No credit for drawings
without accurate size rules. To the right of your drawing, state how big the size rule is. Also,
include any notes that might help you to identify the organism on the lab practical! Have
your instructor check and initial your drawings for credit; all drawings must be completed in
lab and signed by your instructor for credit!
Putman/Pierce College Biol 212 Lab 10/20160422/Page 7
9. Examine the cross section you made of the starfish arm. Draw and label it as per the For the
Lab Report box below.
For the Lab Report:
16. Write out, “16. Phylum Echinodermata, class Asteroidea, Genus species [if known], arm
cross section.” Draw your dissection. Locate, draw and label the pyloric caeca, gonads,
ambulacral ridge, ampulla and tube feet. No credit for drawings without accurate size rules.
To the right of your drawing, state how big the size rule is. Also, include any notes that might
help you to identify the organism on the lab practical! Have your instructor check and initial
your drawings for credit; all drawings must be completed in lab and signed by your instructor
for credit!
10. Examine the other representative(s) of the echinoderm class Asteroidea on display. Make
sure you can identify members of this class for the lab practical. Make sure you ask if there
are any species names your instructor wants you to know.
For the Lab Report:
Write out these questions then answer them:
17. Based on your dissection, were the gonads superior (on top of) or inferior (underneath) to the
pyloric ceca?
18. Does the gonoduct release gametes from the oral or aboral surface?
19. Based on your observations, what are the obvious definitive characteristics of the class
Asteroidea? In other words, how can you tell an asteroid apart from the other four classes of
echinoderms just by looking at it? You may wish to study the other classes before attempting
to answer this question!
Exercise 10.2: Class Ophiuroidea
Introduction
The class Ophiuroidea include the brittle stars, serpent stars and
basket stars. There are about 2,000 described living species. Ophiuroids
have five arms that may be multiply branched and are clearly separated
from the central disc (fig. 10.6). The anus is lacking. The madreporite is
on the aboral surface, mouth on the oral surface. The ambulacral grooves
are closed and tube feet are lacking in this class.
Objective
Objective 13: From a preserved specimen or photograph, give the
Putman/Pierce College Biol 212 Lab 10/20160422/Page 8
Fig. 10.6: Class
Ophiuroidea, Ophiactis.
Life size.
phylum, class and common names of typical representatives of the echinoderm class
Ophiuroidea. Learn any species names assigned by your instructor.
Materials and Methods
*Platomount or dried or preserved representatives of the class Ophiuroidea.
1. Examine the representative(s) of the echinoderm class Ophuroidea on display. If dried
representatives are presented, please do not touch them as they are very fragile. Examine the
specimen(s) while answering the For the Lab Report question below.
For the Lab Report:
Write out these questions then answer them:
20. What are the obvious definitive characteristics of the class Ophiuroidea?
Exercise 10.3: Class Echinoidea
Introduction
Echinoids include the sea urchins, sea biscuits and sand dollars.
There are about 950 described living species. Echinoids have a globose
(Fib. 10.7) to flattened body, without arms, that is divided into five
regions. Some ossicles are modified into articulated spines.
Fig. 10.7: Class
Echinoidea,
Strongylocentrotus. 8 cm
wide.
Objective
Objective 14: From a preserved specimen or photograph, give the
phylum, class and common names of typical representatives of the
echinoderm class Echinoidea. Learn any species names assigned by your instructor.
Materials and Methods
*Plastomount or dried or preserved representatives of the class Echinoidea.
1. Examine the representative(s) of the echinoderm class Echinoidea on display. Make sure you
can identify members of this class for the lab practical. Examine the specimen(s) while
answering the question in the For the Lab Report box below.
For the Lab Report:
Write out these questions then answer them:
21. Based on your observations, what are the obvious definitive characteristics of the class
Echinoidea?
Putman/Pierce College Biol 212 Lab 10/20160422/Page 9
Exercise 10.4: Class Holothuroidea
Introduction
The holothuroids, or sea cucumbers,
include about 1,150 described living species.
They are orally-aborally elongated, with the mouth
at one end of a cylindrical body, the anus at the
Fig. 10.8: Class Holothuroidea,
other. A cluster of five feeding tentacles are located Cucumaria. 15 cm in length.
around the mouth. The madreporite is internal.
There are usually five rows of tube feet running
along the sides of the body, although some holothuroids lack tube feet on the “dorsal” surface of
the animal, and some lack tube feet entirely. Ossicles are reduced so that holothuroids are
relatively soft bodied.
Objective
Objective 15: From a preserved specimen or photograph, give the phylum, class and common
names of typical representatives of the echinoderm class Holothuroidea. Learn any species
names assigned by your instructor.
Materials and Methods
*Plastomount or preserved representative(s) of the class Holothuroidea
1. Examine the representative(s) of the echinoderm class Holothuroidea on display. Make sure
you can identify members of this class for the lab practical. Examine the specimen(s) while
answering the question in the For the Lab Report box below.
For the Lab Report:
Write out these questions then answer them:
22. Based on your observations, what are the obvious definitive characteristics of the class
Holothuroidea?
Exercise 11.5: Class Crinoidea
Introduction
The class Crinoidea includes the sea lilies and feather stars. The oral surface of the
animal faces upward, the aboral surface, which may or may not have a stalk, downward. Both the
mouth and anus are on the oral surface. There are five ambulacral grooves on the oral surface of
Putman/Pierce College Biol 212 Lab 10/20160422/Page 10
the central area. Crinoids possess modified tube feet. There are
over 600 living species, with over 5,000 extinct species in the
fossil record. Feather stars are capable of using their rays to
swim.
Objective
Objective 16. From a preserved specimen or photograph, give
the phylum, class and common names of typical representatives
of the echinoderm class Crinoidea.
Materials and Methods
Fig. 10.9: Class Crinoidea,
Neometra.
* Plastomount, dried or preserved representatives of class
Crinoidea
1. Examine the representative(s) of the echinoderm class Crinoidea on display. Make sure you
can identify members of this class for the lab practical. Examine the specimen(s) while
answering the question in the For the Lab Report box below.
For the Lab Report:
Write out these questions then answer them:
23. Based on your observations, what are the obvious definitive characteristics of the class
Crinoidea?
~When you’re finished, help clean up!
1. Is your lab bench clean and wiped down with antiseptic solution?
2. Are all materials returned to their proper place?
3. Is the oil immersion objective of your microscope clean?
4. Is the lowest-power objective of your microscope positioned down?
5. Is the power cord draped loosely about one of the oculars?
6. Is your microscope put away?
7. Is all refuse disposed of properly?
8. Is the lab generally in order?
Putman/Pierce College Biol 212 Lab 10/20160422/Page 11