MEDUSAE OF THE WORLD. 



THE HYDROMEDUSAE. 



Order LEPTOMEDUS.E (Continued). 



Family EUCOPIDAE Gegenbaur, 1856. 



Eucopidtf, Gegenbaur, 1856, Zeit. fiir wissen. Zool., Bd. 8, p. 241. — Haeckel, 1879, Syst. der Mcdusen, p. 161. — Maas, 1897, 

 Mem. Museum Comp. Zool. at Harvard College, vol. 23, p. 20; 1905, Craspedoten Medusen der Siboga Exped., Monog. 

 10, p. 31. 



FAMILY CHARACTERS. 



Leptomedusae with lithocysts, and with less than 8 radial-canals upon which the gonads 

 are developed. 



The great majority of these medusae have 4 radial-canals, and none are known to have 

 more than 6 radial-canals. They develop through alternation of generations from Cam- 

 panularian hydroids. The Eucopidae are possibly derived from the more simply organized 

 Thaumantiadae. Indeed, the young medusae of the subfamily Eireninae of the Eucopidae lack 

 marginal lithocysts, and in this respect resemble the adult stages of the medusae ot the Thau- 

 mantiadae. 



Asexual budding is exceedingly rare in the medusae of the Eucopidae. In all known forms 

 the marginal ring-canal is simple and does not give rise to blindly ending, centripetal vessels. 



The lithocysts are open or closed folds of the velum at the bell-margin, and the concre- 

 tions are always of ectodermal origin and are ennervated by the inner nerve-ring. 



The Eucopidae, being dependent for their development upon a fixed hydroid stage, are 

 not commonly found far out at sea, but are very abundant along shores, the shallow waters of 

 which afford suitable habitats for their hydroids. 



We may divide the Eucopidae into two cohorts, the first being composed of the sub- 

 families Obelinae and Phialinae in which the stomach either lacks a peduncle or is mounted 

 upon a very short, wide, flaring peduncle, which is always readily distinguished from the 

 elongate, prominent peduncle of the second cohort composed of the subfamilies Euteminae 

 and Eireninae. There are very few intergrading forms with peduncles of only moderate 

 length, and one is never in doubt as to which cohort a given medusa belongs. 



The synopsis of the genera of Eucopidae follows. 



Subfamily Obelin-i : Eucopida' with 8 adradial lithocysts. Manubrium without a well-developed peduncle. 



Eucopella von Lendenfeld, 1883. Degenerate medusa without manubrium or tentacles. The 4 radial-canals give nse to 



side branches upon which gonads are developed. Closed vesicular lithocysts. Hydroid: Eucopella von Lendenfeld. 

 Agastra Hartlaub, 1897. Degenerate medusa without manubrium, but with rudimentary tentacle-bulbs. No cirri, 4 



sac-like gonads upon the 4 simple radial-canals. Closed vesicular lithocysts. 

 Eiiftft Gegenbaur, 1856. Closed vesicular lithocysts upon bell-margin between tentacles. Basal bulbs of tentacles simple 



and hollow and do 170/ extend inward into gelatinous substance of bell. No cirri. Hydroid: Campanulina Van 



Beneden. 

 Obelin Peron and Lesueur, 1809. Closed vesicular lithocysts placed upon subumbrella side of basal bulbs of 8 tentacles. 



Entodermal cores of all tentacles extend inward into gelatinous substance of bell. No cirri. Hydroid is Obeha. 

 Tiaropsis L. Agassiz, 1849. Lithocysts are open folds of velum containing numerous concretions. Entodermal ocellus above 



each lithocyst. Tentacles numerous with simple, hollow basal bulbs. No cirri. Hydroid unknown. 

 Casmetira Hartlaub, 1909. Lithocysts in 8 open folds of the velum. Tentacles of two sorts — large hollow ones arising 



from the bell-margin, and small cirrus-like ones arising from the sides of the exumbrella above the margin and also 



from the margin itself. 



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