Phylum Cnidaria

General Characteristics About 9000 species Simple nervous systemCalled a nerve net. No brainHas tentacles, sometimes very small

that grab prey and pull them to the mouth, thus they are predators.

They might be sessile or motile, or each at different times of their life.

General Characteristics Cont’d-• Either tubular or bell shaped(Polyp or medusa form)• Only animal with

cnidocytes• Cnidocytes-specialized

stinging cells (on tentacle)• All marine (aquatic) except For a few freshwater examples

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• Cnidarians’ bodies are organized around the (hollow stomach area)gastrovascular cavity, where digestion takes place• GV has a single opening that

serves as both mouth and anus

2 Layers of Cells

–Diploblastic means that its body developes from 2 layers of cells.–Gastrodermis: lines GV cavity–Epidermis: lines the outside of

the body (the skin)

• In between the two layers is the mesoglea- a jelly-like substance.

Cnidarian Body Wall

Stinging Cells

• Have Cnidocytes which are cells that contain nematocysts: barbed thread-like structures inside the cnidocyte that shoots out and can puncture and poison or entangle prey

Cnidocyte

Feeding

• Using tentacles they touch the prey and inject the “poison” into them with nematocysts. This “stuns” or paralyzed the prey. WHY? So it wont tear its tentacles off in the struggle.• Inner gastrodermis secretes digestive juices into gastrovascular cavity which digests food and circulates nutrients

Feeding Cont.

Nervous and Movement

•Have a nerve net & sensory receptors•Muscles help in directional movement & capturing prey

Life Cycles

• Cnidarians have two body forms that are representative of the sexual and asexual life cycles that they undergo.

–Polyp–Medusa

Polyp

–Usually attaches to a substrate at the aboral end (the end away from tentacles)–Oral end is surrounded by feeding

tentaclesUsually the asexual reproductive form

Medusa

Sexual Reproductive form (but hermaphroditic)

Shaped like an upside-down bowlTentacles surround the mouth that is

housed underneath the bell

• When cnidarians display both forms at some point in their lives, they are said to display dimorphism.

_________________________ Both sexual and asexual Sexual

Gametes (sperm and egg)released into water. Fertilization takes place to create free-swimming larvae

AsexualBy budding

Generalized Cnidarian Life Cycle

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• Scyphozoa: Jellyfish

• Anthozoa: Sea anemones & Corals

• Hydrozoa: Hydra

• Cubozoa: Box Jellies

Class Hydrozoa

• Ex. Hydras

Includes hydras, fire corals, and Portuguese Man of War

Class Scyphozoa

• True Jellyfish

Cubozoans• Similar to Scyphozoans, except that

their medusa is cuboidal• Includes the box jellyfish–1 of the 10 most venomous

animals on the planet

Class Anthozoa

• Polyps that are flower-like• Includes sea anemones, corals,

sea whips, and sea fans