Cnidarians An Overview

Classes of Cnidarians Hydrozoa- Hydra Scyphozoa- Jellyfish Anthozoa- Anemones

General Form Soft bodied Stinging tentacles in circle around mouth

Characteristics Respiration: Through diffusion (directly through tissue) Excretion: Through diffusion Feeding: NEMATOCYSTS poison prey, tentacles bring prey to mouth; many cnidarians have photosynthetic protists living in them (symbiotic relationship)

Internal Transport: Mostly diffusion of gases/wastes & nutrients Response: STATOCYSTS are involved in balance (up/down position) OCELLI “eye spots” detect presence of light NERVE NET- primitive nervous system

Jellyfish Ocelli The red dots at the base of the bell on this jellyfish are the ocelli eye spots) used to detect arease of light & dark

Reproduction: Sexual- release gametes into water; Asexual- through budding off of a polyp

Movement: Epidermal cells expand & contract to help move tentacles & propel animal through water (on jellyfish, the bell shaped body contracts)

Usually exist as polyps HYDROZOANS Usually exist as polyps Asexual or sexual reproduction (some hermaphroditic- both sexes) Polyps have special jobs when living in a colony

Most of life spent as a medusa Known for having nematocysts SCYPHOZOANS Most of life spent as a medusa Known for having nematocysts * When stimulated, harpoon releases toxin to poison & kill prey Both sexual & asexual reproduction

Sexual & asexual reproduction ANTHOZOANS Only polyp stage Sexual & asexual reproduction Have photosynthetic symbionts (contribute energy) Corals exist as colonies & have hard outer shell which houses polyps

Cnidarians in our World Economic Importance Ecological Importance Coral reefs provide habitat for fish that are harvested by humans Coral jewellery Research: anticancer drugs, study of nerve net function Form symbiotic relationships with other animals Corals make up reef habitat

Jellyfish Facts 1. Jellyfishes are made up of more than 95% water. Their bodies are soft and lack a skeletal structure or outer shell. They are delicate and easily damaged. 2. The largest jelly has a bell that reaches 8 feet across & tentacles that extend ½ the length of a football field

3. Jellyfish are considered a delicacy by some- they can be eaten dried & salted or cooked

4. An adult jelly is called a Medusa- it gets its name from the Gorgon Medusa of Greek mythology with hair of writhing snakes.

5. Australia’s box jelly is the most dangerous jellyfish… its toxin is more potent than cobra venom & can kill a person in minutes.