SIPHONOPHORA 123 



Key to the suborders of Siphonophora : 



Oi rnoumatophore present. 

 hi Pneumatophore very large ; nectophores absent. 



Ci I'neumatophore a disc, with a large central gastrozooid 1. Disconectae 



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

 trozooid 2. Cystonectae 



&2 Pneumatophore usually small ; nectophores present ; colony usually 



elongate 3. Physonectae 



Oa Pneumatophore absent ; nectophores very large ; colony swimming rapidly. 



4. Calyconectae 



Suborder 1. DISCONECTAE. 



Siphonophores with a very larg-e 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 daetylozooids or tentacles armed with nemotocysts. 

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

 grouped in 2 families. 



Family YELELLIDAE.* 



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 — Veieiia mutica 



(from Lankester). 

 without the sail: 8 species. 



P. linnaeana 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 whieli 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. 



