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STUDENT OBJECTIVE

Students are introduced to arthropod diversity by studying horseshoe crabs, spiders, barnacles, and Daphnia. Students do a detailed dissection of the crayfish. If time permits, students can key insect specimens to their proper order.

EQUIPMENT	AMOUNT
	(Class of 24 with 8 groups)
Compound microscope Dissecting microscope	1/student 1/student
MATERIALS
Living specimens Daphnia Bakers’ yeast Preserved specimens Horseshoe crab Spider Acorn barnacle Crayfish Lubber grasshopper Various insects to be identified Prepared slides—Daphnia Dissecting pans Dissecting instruments: scissors, forceps, blunt probes, razor blades or scalpels, pins Vaseline	1/student packet/lab   Demonstration 1/student 1/student 1/student 1/student 1/student 1/student 1/student

SOLUTIONS

Congo red stain

PREPARATION

About Three Weeks before Lab

Order living Daphnia and preserved materials as needed to arrive the week before lab.

One Week before Lab

1. Inspect arriving orders for suitability.
2. Congo red preparation: Add 30 mg per 10 ml of water and gently boil; store in dropper bottles.

CLASSROOM SUGGESTIONS

1. A slide show on arthropod diversity can be assembled from various sources of Kodachrome slides. These can be shown in a hallway showcase through a rear projection, automatic projector (Caramate). If the library has a media center, a slide-tape show can be assembled and placed on reserve. The biology videodisc available from WCB/McGraw-Hill Publishers has several images on arthropod diversity.
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. Consider the following;

   — arthropod exoskeleton doesn’t grow with the arthropod, and hence, must be shed periodically leaving the
   animal unprotected during the molt.
   — supporting a really large arthropod requires an exoskeleton that would be prohibitively heavy. And if it was
   kept thin and light, the exoskeleton would buckle and collapse.
   — limitations of an open circulatory system.
   — limitation of a tracheole, gill and/or booklung gas exchange systems.

2. Arthropod segments are often fused, making distinct body regions (head, thorax, and abdomen).
   — Arthropod segments are surrounded by chitinous exoskeleton, whereas the annelid is covered
   by a moist collagenous cuticle.
   — Arthropod segments have highly developed structures for locomotion (jointed appendages) whereas the
   annelid segments may have bristle-like setae for locomotion.
3. — Sessile organisms show no symmetry, or have radial symmetry.
   — Motile organisms have bilateral symmetry.

SUPPLEMENTAL MATERIALS