Cnidaria and Ctenophore Key Concepts: Classes, Structures, and Reproduction

Cnidaria -

A group of simple aquatic animals like jellyfish, corals, and sea anemones that have stinging cells.

Cnidocytes -

Special cells in cnidarians that contain stinging structures used to catch prey or defend themselves.

Nematocytes -

The stinging capsules inside cnidocytes that shoot out a tiny harpoon with toxin.

Hydrozoa -

A class of cnidarians that includes hydra and some colonial jellyfish.

Scyphozoa -

The class of true jellyfish that spend most of their life in the medusa form.

Cubazoa -

Box jellyfish that have cube-shaped bodies and very strong venom.

Anthozoa -

A class of cnidarians that includes corals and sea anemones and only live in the polyp form.

Polyp -

A body form that is tube-shaped and attached to a surface, with tentacles facing upward.

Medusa -

A free-swimming, umbrella-shaped body form like a jellyfish.

Statocyst -

A sensory organ that helps the animal detect balance and orientation in the water.

Ocelli -

Simple eye spots that can sense light.

Planula Larva -

The free-swimming larval stage of many cnidarians before they attach and grow.

Strobilation -

A type of reproduction where a polyp divides into many stacked segments that become young jellyfish.

Ephyra -

The young jellyfish stage that forms during strobilation.

Siphonophora -

A group of colonial cnidarians made of many specialized individuals working together (like the Portuguese man-of-war).

Pneumatophore -

A gas-filled float that helps some cnidarians stay at the water's surface.

Irukandji -

A very small but highly venomous type of box jellyfish.

Scleractinia -

Stony corals that build hard calcium carbonate skeletons and form coral reefs.

Ceriantipatharia -

A group that includes tube anemones and black corals.

Octocorals -

Soft corals that have eight tentacles on each polyp.

Ctenophores -

Comb jellies, a separate group of marine animals that move using rows of cilia.

Colloblasts -

Sticky cells in comb jellies used to capture prey instead of stinging cells.