Comb jellyfishes

    Comb jellies are similar to cnidarian jellyfishes in general appearance, but differ in lacking tentacles or stinging cells. Some species of the gooseberry jelly group have a pair (never more--another difference from the many-tentacled cnidarians) of trailing tendrils equipped with colloblast cells that secrete a sticky substance that captures microscopic organisms as food. None are venomous. Other species, such as the flat comb jelly (genus Beroe), have a large mouth-like orifice that is used in capturing large prey items such as prawns, plankton and small fishes.

    The name comb jelly comes from the numerous tiny guanine plates on the outer body. The plates form eight rows of combs. These rows of rectangular plates are controlled by nervous actions and propel the ctenophore through the water. Thus, unlike the passive mobility of cnidarian jellies, the comb jellies have some control of their direction.

    The common Pacific comb jellyfish, Beroe, is a flat, nearly invisible predator. They 
are only visible when seen under special lighting, which also illuminates the tiny combs 
along the body. The guanine crystals that make up the combs give them the rainbow 
luster when illuminated. Photo by Dr. Robert Sprackland.

    There is one species of ctenophore, Haeckelia rubra, that does have stinging nematocysts on its tentacles, but these are obtained from cnidarian species it eats. 

    There are two classes within the Ctenophora: Nuda, which lacks tentacles, and Tentaculata, whose members have a pair of tentacles.