Section 2

Cnidaria and Ctenophora

• Animals in the phylum Cnidaria can be either sessile polyps or swimming medusae. Some cnidarians alternate between polyp and medusa stages during their life cycles.

• The body of a cnidarian consists of two cell layers—an outer epidermis and an inner gastrodermis—separated by a jellylike mesoglea.

• Cnidarians have cells called cnidocytes, which contain organelles known as nematocysts. When a cnidocyte is stimulated, its nematocyst ejects a filament that can paralyze or ensnare prey.

• The cnidarian nervous system is a diffuse web of interconnected nerve cells called a nerve net.

• The four classes of cnidarians are Hydrozoa (which includes animals such as the hydra), Cubozoa (box jellies), Scyphozoa (jellyfish), and Anthozoa (which includes sea anemones and corals).

• Hydrozoans may live as polyps, medusae, or mixed colonies of polyps and medusae. Cubozoans and scyphozoans spend most of their lives as medusae. Anthozoans live only as polyps.

• Animals in the phylum Ctenophora move through the water by beating the cilia that occur in eight rows on the outside of a ctenophore's body.

• Ctenophores capture prey with a sticky substance secreted by cells called colloblasts, which are usually located on a pair of tentacles.

• An apical organ at one end of the body enables ctenophores to sense their orientation in the water. Most ctenophores are hermaphroditic, and many are bioluminescent.

Vocabulary medusa (p. 676) polyp (p. 676) epidermis (p. 676) gastrodermis (p. 676)

mesoglea (p. 676) gastrovascular cavity (p. 676) tentacle (p. 676) cnidocyte (p. 677)

nematocyst (p. 677) nerve net (p. 677) planula (p. 680) coral reef (p. 681)

colloblast (p. 682) apical organ (p. 682) bioluminescence (p. 682)

Sirens Sleep Solution

Sirens Sleep Solution

Discover How To Sleep In Peace And Harmony In A World Full Of Uncertainty And Dramatically Improve Your Quality Of Life Today! Finally You Can Fully Equip Yourself With These “Must Have” Tools For Achieving Peace And Calmness And Live A Life Of Comfort That You Deserve!

Get My Free Ebook

Post a comment