Exercise 18 - Simple Animal Phyla

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	1/student
Dissecting microscope	1/student
Aquarium, saltwater	1/lab

MATERIALS

PREPARATION

Three to Four Weeks before Lab

Order preserved specimens and prepared slides as needed.

Week before Lab

All preserved specimens should be in inspected for useability. The dissecting instruments should be clean and sharp.

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.

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 becuase 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. All exchange gases across their body surfaces. None have special respiratory structures. Metabolic and activity rates are often low compared to other animals and body size is usually small without compact tissue masses as in large animals. Consequently, diffusion of gases into and out of the body is sufficient to satisfy demand.

SUPPLEMENTAL MATERIALS

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

Freshwater Sponge-Spongila lacustris, an eight-minute VCR showing development from gemmutes. Concord, NH: Essayo.

Primitive Metazoan Phyla, slide set. Burlington, NC: REX Educational Resources Comp. #L1028