SIPHONOPHOEA 123 



Key to the suborders of Siphonophora : 



o t Pneumatophore present. 

 &! Pneumatophore very large ; nectophores absent. 



c t Pneumatophore a disc, with a large central gastrozooid 1. DISCONECTAE 



c 2 Pneumatophore more or less cylindrical, without a large central gas- 

 trozooid 2. CYSTONECTAE 



& 2 Pneumatophore usually small ? nectophores present ; colony usually 



elongate 3. PHYSONECTAE 



a, Pneumatophore absent ; nectophores very large ; colony swimming rapidly. 



4. CALYCONECTAE 



SUBORDER 1. DISCONECTAE. 



Siphonophores with a very large disc-like pneumatophore and with- 

 out swimming individuals (Fig. 205). The pneumatophore has a com- 

 plex structure; it contains a number of air chambers and beneath its 

 center is a single large trunk which bears the principal mouth and 

 stomach of the colony. Surrounding the trunk are small reproductive 

 individuals which bear the gonads, and surrounding them near the rim 

 of the disc are long dactylozooids or tentacles armed with nemotocysts. 

 The whole colony bears a striking resemblance to a medusa: 36 species, 

 grouped in 2 families. 



FAMILY VELELLIDAE.* 



Pneumatophore a circular or elliptical disc without marginal inden- 

 tations: about 30 species. 



1. VELELLA Bosc. Disc elliptical and very flat and with an ele- 

 vated ridge passing diagonally across it, which acts as a sail as the 

 animal floats on the surface of the water: 13 



species. 



V. mutica Bosc (Fig. 206). Length of 

 disc 4 cm., breadth 2 cm. : along the South 

 Atlantic coast, occasionally off New England. 



2. PORPITA Lamarck. Disc circular, and Fig. 206 Velella mutica 



(from Lankester). 

 without the sail: 8 species. 



P. linnseana Lesson (Fig. 205). Diameter of disc 3 to 5 cm.: along 

 the South Atlantic coast, occasionally off New England. 



SUBORDER 2. CYSTONECTAE. 



Siphonophores with a very large pneumatophore from the under side 

 of which project nutritive individuals, no large central trunk and no 

 swimming individuals being present. The colony floats on the surface 

 of the water, often carried by currents and the wind long distances, 

 and can sink beneath the surface by compressing the pneumatophore 



* See "The Porpitidae and Velellidae," by A. Agassiz, Mem. Mus. Comp. Zool., 

 Vol. 8, 1883. 



