SCYPHOZOA 



125 



Family DIPHYIDAE. 



Two nectophores present: 10 genera and about 35 species. 



DiPHYES Cuvier. Nectophores conical and veiy large; the remain- 

 der of colony can be retracted into a groove in the nectophores and is 

 constantly being shortened by the breaking off of 

 the terminal and oldest groups of individuals, each 

 gi'oup (which is called an Eudoxia) thus separated 

 leading an independent life and becoming sexually 

 mature : 6 species. 



D. bipartita Costa (Fig. 208). Total length 30 

 mm.; length of the nectophores 10 mm.; body trans- 

 parent: tropical and subtropical Atlantic; Mediter- 

 ranean; occasionally on New England coast; often 

 very common. 



Class 2. SCYPHOZOA. (Scyphomedusae.) 



These animals have usually an alternation of 



generations, in a few (Pelagia), however, the medu- 



soid generation and in others {Lucernaria) the 



hydroid alone being present. The medusoid plays 



a much more conspicuous part than the hydroid. 



The latter is a small, usually non-colonial animal 



called the scyphistoma, which is less than a centimeter in height and 



resembles the fresh-water Hydra in appearance (Fig. 217, A). It differs 



from Hydra, however, in that the aboral end is fixed to the bottom in a 



cup formed of the perisarc, in the possession of four longitudinal folds 



of the entoderm called mesenteries which project into the gastrovascular 



space and of an ectodermal gullet. The scyphistoma is an asexual 



animal and reproduces by budding exclusively. New scyphistomas may 



be produced by a process of lateral budding from stolons sent off from 



the foot. The medusoid generation is produced by a process of terminal 



budding called strobilation (Fig. 217, B). The scyphistoma grows in 



height and a series of constrictions appear which divide it into a number 



of discs. Each disc is called an ephyra (Fig. 217, C) and is a young 



medusa or jellyfish, which on becoming free grows in time to be a sexual 



animal. 



The medusa which is thus produced is often a large animal; Cyanea 

 may be two meters and more in diameter with tentacles thirty-five 

 meters or more long. It is called acraspedote because the velum, which 

 is so characteristic of the cras^Dedote Hydromedusae, is wanting or 

 rudimentary. The periphery of the bell is lobed or scalloped and may 

 or may not have tentacles. The manubrium is sometimes very long and 



Fig. 208 



Diphyes bipartita 

 (Hargitt). 



