Search This Blog

Tuesday, February 9, 2010

Comb Jellyfish

Comb jellyfish is, in fact, not a jellyfish at all. Jellyfish as a species belong to the phylum, Cnidaria. On the other hand, comb jellies are an entire separate phylum themselves called Ctenophora. The phylum derives it name from a common characteristic shared by the member species, namely a series of vertical ciliary combs that cover the surface of the animal. The word ctnophora is derived from the Greek words ctene, or "comb", and phora, or "bearer". Both, Cnidaria and Ctenophora fall under the same infrakingdom, Coelenterata, and share a number of similarities.

Ctenophores are usually colorless and transparent, although some species are known to have red, black, orange or golden pigmentation. They mostly grow between a size of few centimeters to a foot and half long. Ctenophores tend to have a rainbow effect on the surface of their bodies, even though they are not bioluminescent.

The body of the ctenophores is made up of two layers, the ectoderm (the outer layer) and the gastroderm (the inner layer. The ectoderm is a double layer of cells covered in a mucus-like substance that is secreted by special glands. The gastroderm contains a small cavity that is the stomach and is connected to the mouth with a long gullet. The gullet contains strong enzymes to help digest the food, so that by the time the food reaches the stomach, it is already half digested. The food gets fully digested in the stomach and the waste product is expelled from the body through the mouth itself, and sometimes, through two anal pores that are used very infrequently. The space in between the two layers is filled with a jelly like layer, the mesoglea.

Most known species of comb jellies are spherical or oval in shape and have an extraordinary sense organ, the statocyst, which is at one end of the body. On the other end is the mouth. There are eight comb rows that extend from near the statocyst and they serve as oars to facilitate movement. Each comb row is made up of a series of transverse plates of very large cilia and they are usually fused at the base. These are called combs and they comb jellies derive their name from them.

Some species of comb jellies have two tentacles that emerge from the middle of their bodies and are retractable. Unlike species from the Cnidaria phylum, these tentacles do not have stinging cells, but 'colloblasts' or 'lasso cells'. When the tentacle comes in contact with the prey, sticky threads emerge from the from the colloblasts and entangle the prey.

Ctenophores are free-floating creatures and inhabit almost all the marine waters of the world. Except for one particular species which is parasitic in nature, all comb jellies are carnivorous by nature. Their primary diet usually consists of microscopic plankton and zooplankton. But, comb jellies are also known to consume some young fish, larvae of other animals like crabs, clams and oysters, copepods, worms, small crustaceans and even some species of the Cnidaria phylum

No comments:

Post a Comment