272 COELENTERATA HYDROZOA chap. 



whole branch is enclosed in a common layer of ectoderm. The 

 zooids have scattered capitate tentacles. The Ceratellidae occur 

 in shallow water off the coast of N'ew South Wales, extend up 

 the coast of East Africa as far as Zanzibar, and have also been 

 described from Japan. 



Fam. Pennariidae. — In the hydrosome stage the zooids have 

 numerous oral capitate tentacles scattered on the hypostome, and 

 a single circlet of basilar filiform tentacles. The medusa of 

 Pennaria, a common genus of wide distribution, is known under 

 the name Globiceps. 



Fam. Corynidae.- — In the hydrosome stage the zooids of this 

 family possess numerous capitate tentacles arranged in several 

 circlets or scattered. 



In Gladocoryne the tentacles are branched. Syncoryne is a 

 common and widely distributed genus with numerous unbranched 

 capitate tentacles irregularly distributed over a considerable 

 length of the body-wall of the zooid. In many of the species 

 the gonophores are liberated as Medusae, known by the name 

 Sarsia, provided with four filiform tentacles and a very long 

 manubrium. In some species {S. prolifera and S. siphonophora) 

 the Medusae are reproduced asexually by gemmation from the 

 long manubrium. A common British Anthomedusa of this family 

 is Dipurena, but its hydrosome stage is not known. In the 

 closely related genus Coryne the gonophores are adelocodonic, and 

 exhibit very rudimentary medusoid characters. 



Fam. Olavidae. — This is a large family containing many 

 genera, some with free -swimming Medusae, others with adelo- 

 codonic gonophores. In the former group are included a number 

 of oceanic Medusae of which the hydrosome stage has not yet 

 been discovered. The zooids of the hydrosome have numerous 

 scattered filiform tentacles. The free -swimming Medusae have 

 hollow tentacles. 



Clava contains a common British species with a creeping 

 hydrorhiza frequently attached to shells, and with adelocodonic 

 gonophores. Cordylophora is the genus which has migrated into 

 fresh water in certain European localities (see p. 269). It forms 

 well-developed branching colonies attached to wooden gates and 

 piers or to the brickwork banks of canals. Several Anthomedusae, 

 of which the hydrosome stage is not known, appear to be related 

 to the Medusae of this family, but are sometimes separated as 



