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MAR111 Exercise 8
(10 points)
Name _________________________________
Echinoderms
Echinoderms are characterized by having spiny skin, a water vascular system, and secondary
pentamerous radial symmetry. Echinoderms are exclusively marine.
Taxonomy:
Phylum: Echinodermata – G: “spine skin”
Class: Crinoidea (sea lilies and feather stars) – G: “lily-like”
Class: Asteroidea (sea stars) – G: “star-like”
Class: Ophiuroidea (brittle stars) – G: “snake-like”
Class: Echinoidea (sea urchins) – G: “spine-like”
Class: Holothuroidea (sea cucumbers)
Starfish - bipinnaria larvae and development
1. Look at the starfish bipinnaria larvae under the microscope and the dried starfish specimens.
How does the adult develop from the bipinnaria larva? ______________________________
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2. Look at the sea urchin larvae under the microscope. What are their larvae called?
_____________________________
What type of symmetry do echinoderm larvae have? _____________________________
What type of symmetry do echinoderm adults have? _____________________________
Which planktonic lifestyle to the larvae represent (holo- or mero-)? ______________
Look at one of the preserved starfish Asterias (make sure you wear gloves). First look at the
external anatomy. Notice the 5 arms and central disc area. Echinoderms do not have a
traditional anterior/posterior or dorsal/ventral orientation. Instead, they are considered to have
oral and aboral sides. On the underneath side (oral), you should see the mouth at the center of
the disc and tube feet radiating out in grooves along the bottom of each arm. On the top side
(aboral), notice the small circle that is off center on the disc. This is the madreporite, which
acts like a sieve that allows water in and out of the water vascular system.
3. Label the oral side, aboral side, madreporite, mouth, and tube feet on the diagram below:
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Carefully remove the skin off the aboral side of the central disc and one of the arms to reveal
the internal anatomy. First look at the stomach in the center that is attached to the mouth.
Running along the aboral side of each arm are two strands of pyloric ducts/ceca, which are the
digestive glands. Push these aside to reveal the end parts of the water vascular system. You
may also see gonads under the ducts if the starfish was mature.
The water vascular system in echinoderms powers the hundreds of tube feet, which the
organisms use for locomotion and holding objects. The water vascular system starts at the
madreporite on the aboral side. Water entering is filtered through the madreporite and travels
down a calcified tube called the stone canal. The water is then sent around the circular ring
canal and then diverted down each arm by the radial canals. Ampullae line each side of the
radial canal and are the bulb-shaped object on top of each tube foot. Nerves control the
contraction of the ampullae to extend and hold or retract and release each tube foot.
4. Label these parts of the water vascular system on the diagram on the diagram below:
madreporite, stone canal, ring canal, radial canal, ampullae, and tube feet.
Look at the live and preserved sea urchins. On the bottom (oral) side you may be able to see
the mouth. The mouth of urchins is a complex structure called "Aristotle's lantern".
5. Given what you know about the symmetry of adult echinoderms, how many teeth would
there be in the Aristotle's lantern? __________
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Three types of structures protrude from the outside of the urchins: hard pointy spines (can be
short or tall), long narrow tube feet, and small pinchers on stalks called pedicellaria. Starfish
also have small pedicellaria. Some pedicellaria and spines of urchins and starfish have venom
glands. These are used for defense, to keep objects (like larvae) from settling upon them, and
sometimes for predation.
6. Label the spines, tube feet, and pedicellaria on the diagram below:
Look at a cleaned sea urchin skeleton (also called a "test"). The urchin skeleton has
interlocking plates of calcium carbonate. Each plate has 5 sides, plus one large and sometimes
several smaller tubercules (bumps where the spines were attached). Tiny holes between the
plates are where the tube feet used to protrude through the skeleton.
7. Label the oral side, aboral side, skeletal plates, tubercules, and rows of tube feet pores on the
diagram below:
http://www.daviddarling.info/images/sea_urchin.jpg
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8. Hold the urchin skeleton up to a light and look through the larger opening on the oral side.
The light will pass through the tube feet pores, making them more visible.
How are the tube feet pores arranged on the test? ___________________________________
___________________________________________________________________________
9. Look at the preserved brittle star. How are the arms and central disc of the brittle star
different than the starfish?
___________________________________________________________________________
___________________________________________________________________________
10. Look at the preserved sea cucumber (Cucumaria). Sea cucumbers have bodies that are
elongated on the oral-aboral axis. Tentacles surround the mouth at one end and the anus is at
the other. Draw the sea cucumber below and label the oral and aboral ends:
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