7. Corymorphidae (including the medusa-family Hybocodonidae).—Trophosome solitary polyps, with two whorls of tentacles; gonosome, free medusae or gonophores. Corymorpha (fig. 3), a well-known British genus, sets free a medusa known as Steenstrupia (fig. 22). Here belong the deep-sea genera Monocaulus and Branchiocerianthus, including the largest hydroid polyps known, both genera producing sessile gonophores.
| After Haeckel, System der Medusen, by permission of Gustav Fischer. |
| Fig. 53.—Pteronema darwinii. The apex of the stomach is prolonged into a brood pouch containing embryos. |
8. Dendroclavidae.—Trophosome, polyp with filiform tentacles in three or four whorls. Dendroclava, a hydroid, produces the medusa known as Turritopsis.
9. Clavidae (including the medusa-family Tiaridae (figs. 27 and 51). Trophosome, polyps with scattered filiform tentacles; gonosome, medusae or gonophores, the medusae with hollow tentacles. Clava (fig. 5), a common British hydroid, produces gonophores; so also does Cordylophora, a form inhabiting fresh or brackish water. Turris produces free medusae. Amphinema is a medusan genus of unknown hydroid.
10. Bythotiaridae.—Trophosome unknown; gonosome, free medusae, with deep, bell-shaped umbrella, with interradial gonads on the base of the stomach, with branched radial canals, and correspondingly numerous hollow tentacles. Bythotiara, Sibogita.
11. Corynidae (= hydroid families Corynidae, Syncorynidae and Cladocorynidae + medusan family Sarsiidae).—Trophosome polyps with capitate tentacles, simple or branched, scattered or verticillate; gonosome, free medusae or gonophores. Coryne, a common British hydroid, produces gonophores; Syncoryne, indistinguishable from it, produces medusae known as Sarsia (fig. 51). Cladocoryne is another hydroid genus; Codonium and Dipurena (fig. 50) are medusan genera.
12. Myriothelidae.—The genus Myriothela is a solitary polyp with scattered capitate tentacles, producing sporosacs.
13. Hydrolaridae.—Trophosome (only known in one genus), polyps with two tentacles forming a creeping colony; gonosome, free medusae with four, six or more radial canals, giving off one or more lateral branches which run to the margin of the umbrella, with the stomach produced into four, six or more lobes, upon which the gonads are developed; the mouth with four lips or with a folded margin; the tentacles simple, arranged evenly round the margin of the umbrella. The remarkable hydroid Lar (fig. 11) grows upon the tubes of the worm Sabella and produces a medusa known as Willia. Another medusan genus is Proboscidactyla.
14. Monobrachiidae.—The genus Monobrachium is a colony-forming hydroid which grows upon the shells of bivalve molluscs, each polyp having but a single tentacle. It buds medusae, which, however, are as yet only known in an immature condition (C. Mereschkowsky [41]).
15. Ceratellidae.—Trophosome polyps forming branching colonies of which the stem and main branches are thick and composed of a network of anastomosing coenosarcal tubes covered by a common ectoderm and supported by a thick chitinous perisarc; hydranths similar to those of Coryne; gonosome, sessile gonophores. Ceratella, an exotic genus from the coast of East Africa, New South Wales and Japan. The genera Dehitella Gray and Dendrocoryne Inaba should perhaps be referred to this family; the last-named is regarded by S. Goto [16] as the type of a distinct family, Dendrocorynidae.