274 



COELENTERATA — HYDROZOA 



I'l. 



Fam. Monobrachiidae. — MonohracMum, found in the White 

 Sea by Mereschkowsky, forms a creeping stolon on the shells of 

 I'ellina. The zooids of the hydrosome have only one tentacle. 



Fam. Myriothelidae. — This family contains the single genus 

 Myriothela. The zooid of the hydrosome stage is solitary and is 

 provided, as in the Corynidae, with numerous scattered capitate 

 tentacles. The gonophores are borne by blastostyles situated 

 above the region of the tentacles. In addition to these blastostyles 

 producing gonophores there are, in M. phrygia, supplementary 

 blastostyles which capture the eggs as they escape from the 

 gonophores and hold them until the time when the larva is ready 

 to escape. They were called " claspers " by AUman. In some of 

 the Arctic species Frl. Bonnevie ^ has shown that they are absent. 

 Each zooid of M. phrygia is hermaphrodite. 



Fam. Pelagohydridae.— This family was constituted by 

 Dendy ^ for the reception of Pelagohydra mirabilis, a remarkable 



new species discovered by 

 him on the east coast of 

 the South Island of New 

 Zealand. The hydrosome 

 is solitary and free- 

 swimming, the proximal 

 Terty.yi. portion of the body being 

 modified to form a float, 

 the distal portion form- 

 ing a flexible proboscis 

 terminated by the mouth 

 and a group of scattered 

 manubrial tentacles. The 

 tentacles are filiform and 

 Fi, The float ; Scattered over the surface 



Medusae 

 are developed on stolons 

 between the tentacles of the float. They have tentacles arranged 

 in four radial groups of five each, at the margin of the umbrella. 



As pointed out by Hartlaub,^ Pelagohydra is not the only, 

 genus in which the hydrosome floats. Three species of the genus 

 Margelopsis have been found that have pelagic habits, and two 



Fio. 134. — Pelagohydra mirabilis. 



M, position of the mouth; 2t'ft.i^;, tilamentous „f ii,„ flmf 

 tentaeles of the float. (After Dendy.^ "'■ ''"" ^^"'''^■ 



^ Zeitschr. f. wiss. Zool. Ixiii. 1898, p. 489. 

 ^ Quart. Journ. Micr. Sci. xlvi. .1902, p. 1. ^ Zool. ZentralU. x. 1903, p. 27. 



