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STUDENT OBJECTIVE

Students dissect an earthworm and a clam. A demonstration dissection of a squid is available in the lab. Diversity in the molluscs is illustrated. Segmentation and tube-within-a-tube body plans are illustrated.

EQUIPMENT	AMOUNT
	(Class of 24 with 8 groups)
Compound microscope Dissecting microscope	1/student 1/student
MATERIALS
Living specimens Earthworms (night crawlers) Preserved specimens Polychaete worms, whole and dissected Leeches, whole Chiton, whole and dissected Snail, whole Squid, whole and dissected Scaphopod, whole and dissected Clam, whole Prepared slides (sharing possible to reduce costs) Earthworm, cross section (CBS#30-7246) Clam, cross section (CBS#30-7198)* Beaker Dissection pan Dissecting instruments: scissors, forceps, blunt probe, razor blade or scalpel, pins	1/student   Demonstration Demonstration Demonstration Demonstration Demonstration Demonstration 1/student   1/student 1/student 2/lab 1/student 1/student

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

SOLUTIONS

10% ethanol

PREPARATION

About Three Weeks before Lab

A biological supply house or local source of large earthworms should be located and an order placed for the week of lab. Live worms can be kept in a refrigerator. Preserved specimens and prepared slides should be ordered as needed to arrive one week before lab.

One Week before Lab

1. Inspect arriving orders for suitability.
2. Clean and check dissecting instruments.
3. Ethanol preparation:

Day before Lab

Set up specimens demonstrating diversity of annelids and molluscs. Prepare squid dissection and cover with wet cloth and plastic wrap.

Notes

Preserved earthworms can be used in place of ethanol-killed live ones.

CLASSROOM SUGGESTIONS

1. A slide show on diversity can be developed with Kodachrome slides from various sources and run continuously in a hallway showcase using a rear projection, automatic projector (Caramate). If the library has a media center, a slide-tape show on diversity can be developed and made available there. The biology videodisc available from WCB/McGraw-Hill Publishers contains several images that illustrate diversity and could be interfaced with a computer in an instruction/quiz format.
2. 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. Earthworms exchange gases across their moist body surfaces with the air; in heavy rains, their burrows become filled with water. Water has a lower concentration of dissolved oxygen than air. Selection has favored those worms whose behavior brings them to the surface as oxygen levels in the blood drop.
2. Annelids and molluscs have several well-developed organ systems and are organized on a bilaterally tube within a tube body plan. Their behavioral capabilities are greater than those of nematodes and cnidarians. While nematodes also have a bilateral tube within a tube body plan, their organ systems are not as well developed. The cnidarians have an incomplete digestive system and lack well-defined organs beyond the reproductive system. They are radially symmetrical and not as behaviorally diverse as the others.
3. Nudibranchs, squids and octopii lack calcareous shells, yet are molluscs. Barnacles, bryozoans, and corals can produce calcareous exoskeleton which could be considered shells. They clearly are not molluscs.

SUPPLEMENTAL MATERIALS