Download INVERTEBRATE LAB

INVERTEBRATE LAB
Objectives:
By the end of this lab you should be able to:
1. Describe the major characteristics of the Cnidaria and Platyhelminthes.
2. Describe the typical habitat and the ecological niche of each species observed in lab.
3. Describe the movement and type of nutrition of each organism.
4. Describe the anatomy of each species.
Phylum Cnidaria
The Cnidaria are fairly simple animals with a tissue or rudimentary organ level of development and radial
symmetry. The phylum consists of 10,000 species commonly known as jellyfish, sea anemones, and corals. The
name of the phylum is taken from the term cnidocytes which are stinging cells found in the outer layer, the
epidermis, of these animals. The inner layer is the gastrodermis that lines the digestive system. A gelatinous layer,
the mesoglea, is found between these two cell layers. The Cnidarians have two adult body forms, the freeswimming medusa and the sedentary polyp. A free-swimming planula is the larval stage and is produced from a
fertilized egg. Eventually it settles down and develops into a polyp. The phylum consists of three classes:
Hydrozoa which includes Hydra, Obelia, and Portuguuese man-of-war; Scyphozoa which consists of marine
jellyfish; and Anthozoa which includes sea anemones and corals.
Hydra (Class Hydrozoa) has only the polyp state in its life cycle. With its well-defined tissues (gastrovascular
cavity, nervous system, and gonads), it is capable of responding to its environment with predictable behaviors.
Observe living Hydra using a dissecting microscope and refer to appropriate diagrams. Observe the movement and
changing shapes. Sketch a Hydra and label its structures. Identify the mouth, tentacles, and body column. Gently
poke it with a probe and watch its response.
a. Describe the behavior you observe.
b. Do you see evidence of a nervous system and contractile cells?
c. Can you see cnidocytes?
d. What advantages does radial symmetry have for a sessile animal?
f. Drop a few brine shrimp into the water with your hydra and observe the response. This is a favorite prey of Hydra
and you may be able to watch it feed. Describe what you see.
g. What happens to the wastes after the edible parts of the brine shimp have been absorbed?
Look at species of Scyphozoa and Anthozoa on display in the lab.
Check out this web site: http://www.microscopy-uk.org.uk/mag/artjan99/janhydra.html
Phylum Platyhelminthes
Flatworms in the class Turbellaria are acoelomates with three body layers and an organ/system level of
development. Flatworms show cephalization with a concentration of sense organs in the head region and bilateral
symmetry. These features are adaptations for locomotion where the ability to detect and respond to stimuli
encountered as the animal moves along is an advantage.
Examine a living planarian using a dissecting scope. Locate the eyespots which form a simple eye without a lens.
The eye is cup-shaped with heavily pigmented cells forming a retina and sensory neurons that lead to the ‘brain’
which is a collection of cell bodies of neurons. The planaria can detect the direction and intensity of light.
h. Would you expect a planaria to be able to see your face as you watch it? Explain.
i. Oberve the locomotion of your planaria. What happens when you gently touch the planaria’s head or posterior
end with a probe? Gently turn it over and observe the underside. Can it right itself? Would you expect a planaria
to have muscles?
j.Determine whether your planaria are photophobic or phototropic by allowing them to choose between a well lit
area and one that is dark. Which do your planaria seem to prefer? How long does it take for the planaria to move to
a different area?
Planaria are scavengers and feed on any dead animal material they can find. When they locate a suitable
food source they stick out a tube called a pharynx. They use this pharynx to place digestive juices into the
corpse, then suck it up into their digestive tract. Any solid wastes are released back out through this same
structure.
k. Place fresh meat or cooked egg yolk in the dish with a few planaria. Describe their response. How do
they eat?
l. Look at other flatworms (Trematoda and Cestoda) placed in the lab. Sketch them.