Fam. 1. Antipathidae.—In this family the zooids have six tentacles and six or ten mesenteries. It includes nearly all the familiar genera, such as Stichopathes, Cirripathes, Antipathes, Antipathella, Cladopathes, and Bathypathes. Schizopathes and its allies occurring in deep water are the forms regarded by Brook as dimorphic.
Fig. 178.—A portion of a branch of Antipathes ternatensis, showing three zooids and the horny axis beset with thorn-like projections. (After Schultze.)
Fam. 2. Leiopathidae.—This family includes the single genus Leiopathes of the Mediterranean Sea. It is distinguished from the others by the presence of twelve mesenteries.
Fam. 3. Dendrobrachiidae.—This family also consists of a single genus, Dendrobrachia, from 400 fathoms in the South Atlantic. It is distinguished by having pinnate retractile tentacles.
Order VI. Cerianthidea.
This order contains the remarkable Sea-anemone called Cerianthus. Two of the species have been placed in separate genera, but they do not appear to be of more than sub-generic rank. Cerianthus has a long cylindrical body with a double crown of numerous long tentacles at the oral extremity and tapering to a blunt point or rounded at the aboral extremity.
There are numerous mesenteries, which increase in number by the addition of bilateral pairs, arising only in the ventral inter-mesenteric space throughout the greater part, if not the whole, of the life of the zooid. The right mesentery of each young pair is always more advanced than the left, so that the mesenteries have the appearance of arising alternately right and left. None of the mesenteries bear conspicuous bands of retractor muscles. The movements of the body are effected by a thick band of longitudinal fibres lying between the ectoderm and the mesogloea in the body-wall.
The absence or very slight development of muscles on the mesenteries renders it difficult to recognise the homologues of the protocnemes of other Zoantharia in the adult. From the evidence of embryology, however, it seems certain that the six dorsal pairs of mesenteries represent the protocnemes (Fig. 163, 3, p. [368]) and the others are metacnemes.
The stomodaeum exhibits a single long deep siphonoglyph, which is probably dorsal in position.