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STUDENT OBJECTIVE

Stages in the life cycles of simple invertebrates (Porifera, Cnidaria, Platyhelminthes, and Nematoda) are studied. The similarities and differences of body plan, symmetry, coelomic cavity, and levels of organization are observed.

EQUIPMENT	AMOUNT
	(Class of 24 with 8 groups)
Compound microscope Dissecting microscope Aquarium, saltwater	1/student 1/student 1/lab
MATERIALS
Lens tissue Preserved specimen Leucosolenia (CBS#P26) Gonionemus (CBS#P107)* Metridium (CBS#P160C)* Taenia (CBS#245C)* Ascaris (CBS#P265C)* Prepared slides (sharing possible to reduce costs) Hydra, longitudinal section (CBS#30-6052)* Obelia, longitudinal section (CBS#30-6124)* Dugesia, cross section and whole mount (CBS#30-6330, 30-6312)* Clonorchis sinensis or other fluke, whole mount (CBS#30-6370)* Leucosolenia, longitudinal section (CBS#30-5872)* Tapeworm, scolex and proglottids (CBS#30-6718)* Ascaris, cross section (CBS#30-6918)* Living specimen Dugesia (CBS#13-2950)* Hydra (CBS#13-2800)* Petri dish Liver, raw Dissection pan Dissection instruments: scissors, forceps, blunt probe, string, razor blades (2) or scalpel, pins Newspapers and plastic bag (disposal of Ascaris) Watch glass Spring water 25 mesh sieve 200 mesh sieve Soil Baerman Apparatus 6 inch funnel bed sheeting rubber tubing pinch cock	1/student 1/student Demonstration Demonstration 1/student   1/student 1/student 1/student 1/student 1/student 1/student 1/student   culture/lab culture/lab 1/student 200 g/lab 1/student   24 sets/lab 1/lab 24/lab 1 liter/lab 1/lab 1/lab 100g/lab 1/lab

*Please refer to the Appendix for name and address of supplier.

PREPARATION

Three to Four Weeks before Lab

Order preserved specimens and prepared slides as needed.

Week before Lab

All preserved specimens should be inspected for useability. The dissecting instruments should be clean and sharp. Assemble Baerman apparatus (Fig. 18.19).

NOTES

1. A word of caution should be given regarding the handling of Ascaris and its eventual disposal. The eggs are somewhat impervious to most treatments and, in spite of preservation, may be viable. Students should wash hands thoroughly before leaving the laboratory.
2. During the exercise, shield planaria from light and try not to move cultures. They are sensitive to stimulation.

CLASSROOM SUGGESTIONS

1. Because most of this lab is devoted to examination and observation, it is lengthy. Tables can be set up in lab for each phylum with demonstration dissections and specimens available. Slides can be on the same tables. This will reduce expenditure for specimens and slides. Students are divided into groups, assigned a starting phylum, and then rotated through the stations.
2. Many excellent slide sets and films are available and can be used to augment this exercise. These could be placed in a rear projection, automatic projector (Caramate) and run throughout the day in a hallway showcase. If the library has a media center, a tape-slide show on reserve can provide a good out-of-class summary.
3. Check out the links for this lab topic at http://auth.mhhe.com/biosci/genbio/dolphin/ You will find useful materials for developing your lab introduction or summary, and in some cases, you may want to tell students to connect to a particular site for further information.

ANSWERS TO CRITICAL THINKING QUESTIONS

1. Usually the anterior has a cluster of sense organs for light and chemicals at the anterior end, the end that is in front of the animal as it moves through its environment most of the time. Radially symmetrical animals lack this sense organ concentration because there is no anterior end that is usually forward when moving. Consequently, there is no need for clustering of neurons in one location and nervous systems of radially symmetrical animals are often based on rings and are diffuse.
2. Sponges are the simplest because they have no specialized organs. The Cnidarians show increasing complexity which includes a gastrovscular cavity that is an incomplete digestive system and the development of nervous and muscular systems that allow movement. Some species have sense organs. The Platyhelminthes are difficult to interpret as a group because many species are adapted to life as parasites. None the less one sees across the group well developed systems for digestion, excretion and water balance, integration and movement. Nerve cords are found with anterior integrating ganglia and clustered sense organs. All of the animals mentioned do not have body cavitites and are acoelomate. In the nematodes a body cavity is found for the first time. The digestive system is complete with a mouth and anus. The nervous and muscle systems are well developed.
3. Plants at the cellular level characteristically have cellulose cell walls and chloroplasts. Sponges lack cellulose and are green only because they may contin symbiotic algae. Sponges are heterotrophs while most plants are autotrophs.

SUPPLEMENTAL MATERIALS