250 



C(ELENTERATA. 



Some forms differ from the foregoing description in structure and ap- 

 parently in development. Some have only four sen- 

 sory bodies, the places of the other four being taken 

 by tentacles. In these cases the sensory organs 

 lie (Peromedusae) 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 or 

 left vacant (Stauromedusae). This shows that tenta- 

 cles can replace sensory pedicels, and since they have 

 essentially the same structure, they, like the cordylii 

 of the Trachymedusae, are modified tentacles. 

 Order I. Stauromedusae (Calycozoa). 



The best known forms are the Lucernariae 

 (fig. 197), whose exumbrellar surface is drawn out 

 into a stalk by which the animals are 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. 



Fia. 197. Halyclystus 

 auricularia.* (After 

 Clark.) 



Order II. Peromedusae. 



Cup-shaped medusae with four interradial sense bodies. 

 ,sea forms. Pericolpa, Periphylla in the Gulf Stream. 



Mostly high 



Order III. Cubomedusae. 



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

 tropical seas. Charybdea (fig. 198). Development 

 unknown. 



Order IV. Discomedusae. 



These are the most abundant and richest in spe- 

 cies of Scyphomedusae and hence have served as the 

 basis of the foregoing account. The order is subdi- 

 vided according to the characters of the mouth. 



(1) CANNOSTOMJS, mouth triangular without oral 

 tentacles; shape and other features of the ephyra 

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

 Europe is noticeable because its scyphopolyp, de- 

 scribed as Stephanocyplius mirabilis, is parasitic in 

 sponges. Liner ges and Atolla in the Gulf Stream. 



(2) SEM^OSTOMJE, mouth X-shaped with long fringed 

 and folded arms at the corners. Aurelia flamdula * 

 and Cyanea arctica* common in New England, the 

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

 diameter, tentacles extending a hundred feet or 

 more. Pelagia * in our warmer waters. (3) RHIZO- 

 STOME^E.four oral arms, these brancheddichotomously. 



19 ?-,~ c j iar ybdea -phe !nou th and grooves on the arms closed by union 



ipialis.* (From * 



ihek.) of their edges so that many small sucking stomata 



FIG. 



marsi 

 Hatsc 



