The base of a tentacle bisected in the middle line.
The athorome of Physophora, &c., consisting of siphon, tentacle, one or more palpons with palpacles, and one or more gonophores.
From the broader portion of the planula an outgrowth arises which becomes the first tentacle of the cormus.
Foot with anterior transverse groove; a posterior pallial tentacle; generally burrowing.
Further, two distinct types of otocyst can be recognized in the Hydro medusae; that of the Leptolinae, in which the entire organ is ectodermal, concrement-cells and all, and the organ is not a tentaculocyst; and that of the Trachylinae, in which the organ is a tentaculocyst, and the concrement-cells are endodermal, derived from the endoderm of the modified tentacle, while the rest of the organ is ectodermal.
