Sponges

Jellyfish, Sea Anemones Phylum Cnidaria Jellyfish, Sea Anemones

Basic Info Soft-bodied animals with stinging tentacles Live as singles, groups, and in connected colonies Many different species (~9000) All species have stinging cells called nematocysts

Habitat Most species live only in the sea Found in all marine environments

Body Structure All have radial symmetry Polyp – sessile and flowerlike Medusa – motile bell-shaped

Gastrovascular Cavity Three cell layers: Epidermis, mesoglea, gastroderm Gastroderm layer lines a central cavity called the gastrovascular cavity

Form and Function

Nematocysts – stinging cells located in tentacles Shoots a poison dart into prey that paralyzes or kills it. Tentacles – long extensions of the body help push food into the mouth

Body Systems Digestive: Gastrovascular cavity – breaks down food into smaller, digestible pieces. Mouth – entrance for food and exit for wastes Gvc cavity branches in some cnidarians to transport food throughout the body. Respiratory and Excretory: Gastrovascular cavity filled with moving water for exchange of materials Nervous: Simple nerve net concentrated around the mouth

Organs Some medusae have simple organs called statocysts and ocelli Statocysts are used for balance and orientation Ocelli are “eye-spots” that detect light.

Movement No muscular system Epidermal cells can change shape to cause movement Medusae draw in water and expel it under high pressure to move – (jet propulsion) http://www.youtube.com/watch?v=8tp_YxqLtYs

Reproduction Most can reproduce sexually or asexually Budding is common in polyps Medusae often release gametes into the water where they can fertilize internally or externally

Class Hydrozoa Most common is a Hydra Interesting lifecycle Mostly polyp form

Class Scyphozoa Jellyfish Life cycle similar to hydra Can be up to 2 metres wide

Class Anthozoa Anemones and Corals Polyp throughout life cycle Some sea anemones have photosynthetic symbionts

Importance Corals and anemones provide extensive habitats for fish Medical research due to the toxicity of some of the chemicals they produce