SUB-ORDER 1. HYDROIDEA GYMNOBLASTEA (ANTHOMEDUSAE).--Trophosome without hydrothecae or gonothecae, with monopodial type of budding. Gonosome with free medusae or gonophores; medusae usually with ocelli, never with otocysts. The gymnoblastic polyp usually has a distinct perisarc investing the hydrorhiza and the hydrocaulus, sometimes also the hydranth as far as the bases of the tentacles (_Bimeria_); but in such cases the perisarc forms a closely-fitting investment or cuticule on the hydranth, never a hydrotheca standing off from it, as in the next sub-order. The polyps may be solitary, or form colonies, which may be of the spreading or encrusting type, or arborescent, and then always of monopodial growth and budding. In some cases, any polyp of the colony may bud medusae; in other cases, only certain polyps, the blastostyles, have this power. When blastostyles are present, however, they are never enclosed in special gonothecae as in the next sub-order. In this sub-order the characters of the hydranth are very variable, probably owing to the fact that it is exposed and not protected by a hydrotheca, as in Calyptoblastea. [Illustration: FIG. 50.--_Sarsia (Dipurena) gemnifera._ b, The long manubrium, bearing medusiform buds; a, mouth.] [Illustration: FIG. 51.--_Sarsia prolifera._ Ocelli are seen at the base of the tentacles, and also (as an exception) groups of medusiform buds.] Speaking generally, three principal types of hydranth can be distinguished, each with subordinate varieties of form. 1. Club-shaped hydranths with numerous tentacles, generally scattered irregularly, sometimes with a spiral arrangement, or in whorls ("verticillate"). (a) Tentacles filiform; type of _Clava_ (fig. 5), _Cordylophora_, &c. (b) Tentacles capitate, simple; type of _Coryne_ and _Syncoryne_; _Myriothela_ is an aberrant form with some of the tentacles modified as "claspers" to hold the ova. (c) Tentacles capitate, branched, wholly or in part; type of _Cladocoryne_. (d) Tentacles filiform or capitate, tending to be arranged in definite whorls; type of _Stauridium_ (fig. 2), _Cladonema_ and _Pennaria_. 2. Hydranth more shortened, daisy-like in form, with two whorls of tentacles, oral and aboral. (a) Tentacles filiform, simple, radially arranged or scattered irregularly; type of _Tubularia_ (fig. 4), _Corymorpha_ (fig. 3), _Nemopsis_, _Pelagohydra_, &c. (b) Tentacles with a bilateral arrangement, branched tentacles in addition to simple filiform ones; type of _Branchiocerianthus_. 3. Hydranth with a single circlet of tentacles. (a) With filiform tentacles; the commonest type, seen in _Bougainvillea_ (fig. 13), _Eudendrium_, &c. (b) With capitate tentacles; type of _Clavatella_. 4. Hydranth with tentacles reduced below four; type of _Lar_ (fig. 11), _Monobrachium_, &c.