hydrophoraOne of the three divisions into which Huxley and other authors divide the Hydrozoa, the other two being the Discophora and the Siphonophora. The members are, in all cases except that of Hydra, fixed ramified hydrosomes, on which many hydranths and gonophores are developed. The tentacles are either scattered over the hydranths or arranged in one circle round the mouth, or in two circles, one close to the mouth and one near the aboral end. Very generally—for example, in all Sertulariidæ and Tubulariidæ—there is a hard chitinous cuticular skeleton or cœnosarc, which usually gives rise to hydrothecæ, into which the hydranths can be retracted. The gonophores present every variety, from sacs to free-swimming medusoids. The inner margin of the bell in these medusoids is always produced into a velum, and otolithic sacs and eye-spots are very generally disposed at regular intervals round the circumference of the bell. The great majority of what are sometimes termed the naked-eyed medusæ, Gymnophthalmata, are simply the free-swimming gonophores of Hydrophora.