Animals of the phylum ctenophora, often called comb jellies, are oceanic jelly-like organisms distinguished by their eight "comb rows" of cilia used for movement. The term ctenophora means "comb bearer" in Latin. While ctenophores are poorly understood, the beautiful creatures have received increasing attention due to their exhibition in aquariums around the world. One of the amazing things about cnidaria is that their beating cilia act as diffraction gratings, causing the animals to display a rainbow of colors.
In the fairly recent past, the phyla ctenophora and cnidiaria were lumped into one--coelenterata. Now the prevailing view among taxonomists is that the coelenterates are sufficiently different to necessitate two phyla. Unlike cnidarians, ctenophores do not inherently possess nematocysts (stinging cells). Some ctenophores possess and use stinging cells, but these are obtained by eating cnidarians. Most ctenophores capture prey with sticky cells called colloblasts. A few ctenophores have special cilia in their mouths that can pierce into gelatinous prey. All ctenophores are carnivorous and are the prey of jellyfish, sea turtles, and fish.
Unlike cnidarians, ctenophores have a simple life cycle. With the exception of the bottom-dwellers of platyctenida, the entire life of cnidarians is planktonic. Most species are hermaphroditic--a few are capable of self-fertilization. Sperm and eggs unite in the ocean, and the fertilized eggs become free-floating larvae, which gradually grow into adults.
There are probably about 100-150 species of ctenophores. The study of phylum ctenophora has been limited for several reasons. Though lovely, the animals don't seem all that important. They are small and inconspicuous. Many, particularly those in the deep ocean, are incredibly fragile, making them difficult to capture and resulting in scarce fossil records.
Classes of phylum ctenophora
- Cydipidda--coastal ctenophores, usually less than 3cm in diameter, with two tentacles used to reel in prey
- Lobata--coastal ctenophores, larger than those in cydipidda, with sticky lobes to capture prey
- Beroida--coastal elongate ctenophores, often translucent, which typically simply engulf prey (often other ctenophores)
- Platyctenida--benthic (bottom-dwelling) ctenophores found in warm water either on the ocean floor or on the surfaces of other organisms such as sponges
- Ganeshida--oceanic ctenophores
- Thalassocalycida--oceanic ctenophores
- Cestida--oceanic ctenophores