HTDR0ID8 OF EASTERN CANADA 139 



Planula or planule. An oval or pyriform, ciliated, free-swimming embryo, 

 developed from the ovum, which later becomes attached to form the beginning of a 

 hydroid colony. 



Proboscis. The hollow elevation from the body of the hydranth which supports 

 the mouth. 



Sessile. A hydranth or a gonophore is said to be sessile when no pedicel is 

 present. 



Simple. A stem or branch is said to be simple when it consists of a single tvibe. 



Sporosac. The sac that contains the generative elements. 



Stolon. A creeping stem. This may be filiform, or may have cross communica- 

 tions with other stolons to form a network. 



Trophosome. A collective term for all the nutritive zooids that go to make up 

 a colony and structures that are directly connected with them. 



Zooid. One df the individuals, more or less independent, that go to make up a 

 colony. Zooids may be nutritive, generative, defensive or sensory. 



HYDROIDS OF EASTERN CANADA. 



KEY TO FAMILIES. 

 Sub-order A. Gvmnoblastea. 



Ilydroids with hydranths unprotected by hydrothecse and gonophores unprotected 

 by gonangia or other structures having a similar function. 



a Hydranths with scattered filiform tentacles. Clavidce. 



aa Hydranths with one whorl (or two whorls closely approximated) of tentacles 

 around the base. 



h Hydranths with tentacles much reduced in number, even on the nutritive 

 zooids. Lar'utcc. 



hh Hydranths with tentacles not reduced in number. 



c Proboscis conical, dome-shaped or clavate. 



d Colony regularly- branched. 



e Gonophores producing fixed sporosacs. Bimerida\ 



ee Gonophores producing free-swimming sporosacs. 



Dicorynidce. 



eee Gonophores producing free medusae. Bougainvillidw. 



dd Colony not branched, with basal encrusting coenosarc. 



Hydraciinidke. 

 cc Proboscis trumpet-shaped. Eudendridce. 



aaa Hydranths with a proximal and a distal set of filiform tentacles. 



/ Proximal set in a single whorl, distal set in several closely placed whorls. 



Corymorphidcp. 

 ff Proximal and distal set each in a single whorl. Tubularidce. 



aoaa Hydranths with all tentacles capitate. 



g Tentacles scattered. Gonophores producing free medusse. 



Syncorynidce. 



gg Tentacles extremely numerous ajid closely set. Gonophores producing 

 fixed sporosacs. Myriothelidce. 



aaaaa Hydranths with a single whorl of filiform tentacles around the base and 

 capitute tentacles scattered over the rest of the body. Pennarid-r. 



