Phylum Cnidaria 2

Gastrodermis (Endoderm)

Forms gastrovascular cavity

Obelia

Tublularia

Ectoderm

Outer protective layer

Mesoglea

Gel-like layer in between

Functions

Digestion, respiration, circulation, waste removal

Blind

one way in and out

Polyp Stage

• Sessile, asexual reproduction (budding)

• Tentacles & mouth face up

Medusa Stage

• Free-swimming, sexual reproduction

• Tentacles & mouth face down

Planula Larva

Free-swimming stage after fertilization

Cnidocytes

Cells containing stinging nematocysts

Types

• Stinging.

• Toxin-secreting.

• Sticky mucus for trapping.

Osmotic Hypothesis

Water pressure increases

Tension Hypothesis

Stored tension is released

Contractile Hypothesis

Muscle-like squeezing

Symmetry

Radial or biradial

Statocysts

Balance & orientation

Rhopalium

Sensory center

Polyps

Hydrostatic skeleton (fluid-filled)

Medusa

Jet propulsion (contract & relax bell)

Feeding & Digestiion

• Carnivores.

• Tentacles & nematocysts stun & capture prey.

• Digestion in gastrovascular cavity.

Class Hydrozoa

Polyp stage dominant

Gastrozooid

Feeding

Gonozooid

Reproduction

Dactylozooid

Defense

Class Scyphozoa

• Medusa stage dominant.

• Thick mesoglea.

• Cnidocytes in both epidermis & gastrodermis.

Class Cubozoa

• Highly venomous.

• Cube-shaped medusa.

• Complex eyes

Class Anthozoa

• Only polyp stage (no medusa).

• Marine only.

• Gastrovascular cavity divided by septa

Hexacorallia

Anemones & Stony Corals (tentacles in multiples of 6)

Octocorallia

• Soft Corals, Sea Fans (8 tentacles).