SCYPHOMEDUSiE. 



501 



The Orders of the Scyphomedusce. 



The CarybdeidiE are highly specialized forms which are confined to tropical and warm 

 seas. They live upon the bottom in shallow water along coasts, and are not commonly found 

 upon the surface until nearly mature. Their developmental stages are practicall\- unknown 

 and their exact relationship to the other orders of Scyphomedusae is problematical. In com- 

 mon with the Stauromedusae and Coronatae they have 4 perradial stomach-pouches. They 

 bear a remarkable, but wholly superficial, resemblance to the Hydromedusae in the shape of 

 the bell and in the presence of an annular diaphragm which constricts the aperture of the 

 bell-cavity. This velar diaphragm is, however, only an extended part of the subumbrella 

 in Carybdeidae whereas both exumbrella and subumbrella take part in its formation in 

 Hydromedusae. 



The Coronatae are deep-sea and pelagic forms and are therefore of world-wide distri- 

 bution in common with other creatures of similar habits. 



The Semaeostomeae are mainly coastal forms which develop through strobilization from 

 scyphostoma larvae. The genus Pclagia is peculiar, however, in that the larva is not attached, 

 but remains free-swimming and develops directly into the medusa; and thus it is that medusae 

 of this genus are widely distributed, independently of the proximity of land and are found in 

 all warm seas. Certain families, such as the Cyaneidae, are practically confined to the 

 Arctic and Antarctic, and to cold seas; whereas the Pelagidae are found only in warm oceans. 

 On the other hand the genus AurcUia is of world-wide distribution. 



The Rhizostomae form a well-defined order which are clearly descended from the Semae- 

 ostomeae. They are confined to tropical and warm seas and are most abundant in the Malay 

 Archipelago. They develop through strobilization from scyphostoma larvae, and are therefore 

 confined to coastal waters of a depth suitable for the maturation of their attached larvae. 



In the Semaeostomeae and Rhizostomae the egg develops into a pyriform, ciliated planula 

 which is set free from the mouth-folds of its parent and swims freely through the water. Soon 

 it attaches itself by means of its forward end. An ectodermal invagination is said by Goette to 



