250 



GdiLENTERATA. 



Fig. 197. — Hahjclyslu^ 

 anrtculiu ia.* (After 

 Clark.) 



Some forms differ from the foregoing description in structure and ap 

 parently in development. Some have only four sen- 

 sory bodies, tiie places of the other four being taken 

 by tentacles. In these cases the sensory organs 

 lie (Peromedusa;) in the same radii (i.e., interradii) 

 as the sexual organs or (Cubomedusae) the sense 

 organs are perradial. Lastly, some have no sensory 

 organs, their place being either taken by tentacles oi' 

 left vacant (Stauromedusse). This sliovrs that tenta- 

 cles can replace sensory pedicels, and since they have 

 essentially the same structure, they, like the oordylii 

 of the Trachymedusse, are modified tentacles. 

 Order I. Stauromedusae (Calycozoa). 



The best known forms are the Lucernarias 

 (fig. 198), whose extimbrellar surface is drawn out 

 into a stalk by which the animals ai'e attached. The 

 disc is drawn out into eight lobes, each with a cluster of knobbed tentacles. 

 Several species, dark green in color, occur in New England waters. The 

 Tesseridce (unknown in America) are free-swimming. 



Order II. Peromedusse. 



Cup-shaped medusae with four i)iterradial sense bodies. Mostly high 

 sea forms. Pencolpa, Peiip/iyl/a in the Gulf Stream. 



Order III. Cubomedusae. 



Sense organs perradial in position. Occurring in tropical and semi- 

 tropical seas. Charijhdea (fig. 198). Development 

 unknown. 



Order IV. Discomedusse. 

 These are the most abundant and richest in spe- 

 cies of Scyphomednsse and hence have served as the 

 basis of the foregoing account. The order is subdi- 

 vided according to the characters of the mouth. 



(1) Gannostom.e, mouth triangular without oral 

 tentacles; .shape and other features of the ephyra 

 retained in the adult. Nausithoe alhida (fig. 86) of 

 Europe is noticeable because its scyphopolyp, de- 

 scribed as Stephanocjjphus inirabih's, is parasitic in 

 sponges. Liiienjes and Atnlla in the Gulf Stream. 



(2) Sem.eostom.e, mouth X-shapod with long fringed 

 and folded arms at the corners. AureJia flavidida* 

 and Cijiniea ai liiea* commow in New England, the 

 latter, the 'blue jelly,' often very large; disc 7 feet in 

 diameter, tentacles extending a hundred feet or 

 more, l^'lidjin * in our warmer waters. (3) Rhizo- 

 STOME.E.foui- oi-al arms, these brancheddichotomously. 



- (iiiinih,h;i. 'pi,g month and irrooves on the arms closed bv union 

 tliiisi'iii'k.) of their edges so (hat numv small sucking stomata 



Fid. ins.- 



