Exercise 20 - Protostomes II: Arthropods

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 1/student
Dissecting microscope 1/student


MATERIALS

Living specimens
  Daphnia 1/student
  Bakers' yeast packet/lab
Preserved specimens
  Horseshoe crab Demonstration
  Spider 1/student
  Acorn barnacle 1/student
  Crayfish 1/student
  Lubber grasshopper 1/student
  Various insects to be identified
Prepared slides--Daphnia 1/student
Dissecting pans 1/student
Dissecting instruments: scissors, forceps, blunt probes,
                         razor blades or scalpels, pins1/student
Vaseline

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

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 Wm. C. Brown Publishers has several images on arthropod diversity.

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

Bio Sci II, videodisc--contains pictures of these animals. Dubuque, IA: Wm. C. Brown Publishers. See appendix.

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