Monday, April 24, 2006

Cnidarians

BODY PLAN OF CNIDARIANS
- Animals in the phylum Cnidaria are radially symmetrical aquatic invertebrates that are more complex than the sponges. They have tissues and simple organs.
- The cnidarian body is either a sessile polyp or a swimming medusae. Some cnidarians alternate between both types during their life cycles.

The body of a cnidarian consists of two cell layers:
1) an outer epidermis
2) an inner gastrodermis
- The layers are separated by the mesoglea.
- The gastrovascular cavity has a single opening (the mouth) surrounded by tentacles.

FEEDING AND DEFENSE IN CNIDARIANS
- Cnidarians have cells called cnidocytes.
- Each cnidocyte contains a nematocyst.
- When a cnidocyte is stimulated. its nematocyst (stinger) ejects a filament that can paralyze or ensnate prey.

NERVOUS SYSTEM IN CNIDARIANS
- The cnidarian nervous system is a diffuse web of interconnected nerve cells called a nerve net.

CLASSIFICATION OF CNIDARIANS
- The three classes of cnidarians are:
1) Class Hydrozoa
a) This class includes Obelia, man-o-war, and the hydra.
b) Hydrozoans may live as polyps, medusae, or mixed colonies.

2) Class Scyphozoa
a) This class includes jellyfish.
b) Scyphozoans spend most of their lives as medusae.

3) Class Anthzoa
a) This class includes anemones and corals.
b) Anthzoa only live as polyps.

Today's objectives were: Complete 26.2 discussion, 26.2 Cnidarian Section Review, and TEST THURSDAY on 26.1 AND 26.2

The next blogger is Ashley

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