Ctenophora (tĭnŏfˈərə) [key], a small phylum of exclusively
marine, invertebrate animals, commonly known as sea walnuts or
comb jellies. Because they are so delicate that specimens are
difficult to collect, little was known about them until the
advent of blue-water scuba and submersible collecting.
Ctenophores are characterized by eight rows consisting of
ciliated plates called ctenes (combs), which are radially
arranged on the spherical body surface. The animals swim weakly,
powered by those structures. The two hemispheres of the
ctenophore body are marked by a mouth, or oral pole, on the
underside, and an opposite aboral pole, on which is located the
statocyst, a unique sense organ controlling equilibrium. Most
ctenophores resemble biradially symmetrical (see symmetry,
biological) jellyfish (phylum Cnidaria) but lack the cnidarian
whorl of tentacles around the mouth. They lack the specialized
stinging cells (nematocysts) found in coelenterates, but one
species (Haeckelia rubra) incorporates those of its jel