Zoology Cnidaria

Intro To Cnidaria

General  Greek: Cnidos: Means stinging needle  Marine and Freshwater  ~9000 species  Carnivorous  Have a Nervous system  Cnidocytes  Radial Symmetry

Body Structure

Diploblastic: Tissue layers made of two cell layers: Ectoderm: outer layer of skin tissue Endoderm: inner most tissue lining, gives rise to digestive tracts

Between the two layers is a jelly like layer called the Mesoglea. Basically the glue which holds the cells together.

Radial Symmetry: where body patterns are repeated around the center of an animal. Anyway the animal is cut you see a mirror image.

Body: Most body support derived from the water supporting them. Hydrostatic skeleton. This is water or body fluids confined in a cavity of the body. Food enters the mouth by the use of tentacles.

The mouth is located at the center of the organism and is the only opening.

Food is then passed into the Gastrovascular Cavity: This is a digestive chamber with one opening. Both food and waste pass through this cavity as well as different phases in reproduction.

Feeding: Cnidocytes: Stinging cells found on the Ectodermis. These are used in defense and for feeding.

Within each cnidocyte is a nematocyst. This is a poison-filled stinging structure that contains a tightly coiled dart. When these cells are stimulated 1000’s of nematocyst darts shoot into the animal and stun or kill the prey.

Cnidarians are passive predators- eating is by chance- what ever runs into the tentacles

Respiration/Circulation/Excretion After digestion nutrients are usually transported throughout the body by diffusion. Respiration is also done by diffusion.

Response: Nerve Net: loosely organized network of nerves. Uniformly distributed around the body. Statocysts: help the animal determine the direction of gravity. Reproduction

Asexual or Sexual

Polyp: cylindrical body with arm-like tentacles. Asexual through budding. New animal genetically identical to the “parent.” This bud then develops into a larger polyp or medusa

Medusa: Bell shaped body fringed with tentacles and mouth toward the center.

Sexual Reproduction: External fertilization: egg and sperm released into the water. The zygote is a free swimming larva called the Planula. This larva then attaches to a hard surface and develops into a polyp. Then the polyp buds and releases a small medusa called an ephyra. This will then develop into a mature Medusa.

Hydra Drawing

Purpose: To illustrate the body structure of a Hydra.

Obtain a Hydra from the glass vile. Use a pipette to suck out one hydra per group. Using the microscope draw what you see. Then using your coloring book handout, label all the structures you can see. Remember to follow your drawing guidelines.

You will need to make 2 different drawings. One drawing at 100x and the other at 400x. Label any important structures.

Picture Evaluation

First review your biological drawing guidelines. Then make any corrections and/or improvements to your drawings. Next read your drawing rubric. Carefully and honestly evaluate your work using the rubric. Think of the time and effort you put into your work. Can you do better? What can be improved for next time. Write a short summary about your drawings IN your portfolio. Give yourself honest praise and criticism about your work. Using the point scale of your rubric, give yourself a grade on your drawings thus far.