Sponges

Phylum CnidariaJellyfish, 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