38 



HYDROIDA 



Section Filif era K ii h n. 

 Family Clavidae. 



Hydroids forming colonies, with polyps fnsiforni or capitate, the distal part of which is coni- 

 cally tapering. The stinging cells are small and rodformed. The tentacles are filiform, irregularly dis- 

 tributed over the body of the polyp, now and then showing a heterogeneous development or even 

 reduced to a single large tentacle. The endoderm forms a homogeneous gastral cell-layer through 

 the whole of the polyp. The colonies have no calcareous skeleton. 



The family Clavidae, as it is here defined, includes the genus much in dispute Monobrac/iiiini, 

 which has been distinguished by most investigators as the representative of a family of its own, Mo- 

 iiobrachiidac. This family is maintained even by Kiihn (1913), who has obviously failed to notice 

 the significant pointing out by Vanhoffen (1909) of the heterogeneous development of the tentacles 

 of Campaniclnva cliouis Vanhoffen, forming an obvious link between Moiwbracliiiim and the other Cla- 

 vidae. Vanhoffen, therefore, does away with the family Moiiobrac/iiidar and refers Moiiobracliiuin 

 to Clavidae. In this he is rightly followed by vStechow (1913). 



(Jien. Clava Ciinelin. 



The reptant colonies have polyps capitate or subfusiform with filiform tentacles irregularly 

 distributed over the polyp. The proboscis is conically pointed. The hydrocauli are not surrounded 

 by any distinct stiff perisarc. The gonophores are clustered on the polyp below the portion bearing 

 tentacles, or seated on the reptant stolons either solitary or in clusters. 



According to this diagnosis also the genus Rliizogcton must be included under Clava. The two 

 genera have hitherto generally been distinguished on the ground that in Rhizogefon the gonophores 

 are seated on the stolons, while in Clava they are borne by the polyp itself. This criterion, however, 

 is too insignificant to justify a division of genera, and it is also suggested by Stechow (1913) that 

 very likely the two genera have to be united. In his key of genera, indeed, Stechow puts down 

 Rhizogefon. in a jjarenthesis under Clava. 



Clava multicornis (Forskal) Gmelin. 



1775 Hydra multicornis., Forskal, Descriptiones auimalium, p. 131. 



1776 — sqiiatiiata, Miiller, Zoologia Danicjje Prodromus, p. 230. 



1788 Clava parasitica, Gmelin, in Linne: Systema natura Ed. 13, vol. I, p. 3131. 



On the reptant stolons the capitate or almost fusiform polyps are placed in close or opener 

 clusters. Tlie stem of the polyp is without perisarc. The filiform tentacles are irregularly distributed 

 over the distal parts of the polyp. 



The gonophores are cryptomedusoid, and placed in larger or smaller groups like clusters of 

 grapes closely below the portion of the polyp bearing the tentacles. 



