CORONATE — ATOLLA. 561 



Family COLLASPID^ Haeckel, 1880. 



Collaipidx, Haeckel, 1880, S)st. der Medusen, p. 488. — Vanhoffen, 1906, Nordisches Plankton, Nr. 11, p. 44. 

 Aiollidrz, BiGELow, H. B., 1909, Mem. Mus. Comp. Zool. at Harvard College, vol. 37, pp. 21, 37. 



FAMILY CHARACTERS. 



Coronatae with numerous (more than 8) marginal sense-organs which alternate with an 

 equal number of tentacles. Marginal lappets twice as numerous as the tentacles. 



Atolla is the onl)- known genus. 



Genus ATOLLA Haeckel, 1880, sensu Fewkes. 



Atolla+CoUaspis, Haeckel, 1880, Syst. der Medusen, p. 488; 188 1, Deep-Sea Medus.T, Challenger Report, Zool., vol.4, p. ill. 



Atolla, Fewkes, 1886, Report Commiss. Fish and Fisheries U. S. A. for 1884, p. 934; ( r) Ephyroides, 1885; Ihid. for 1883, 

 p. 597; and i885, p. 948; 1889, p. 532. — Vanhoffen, 1892, Ergeb. der Plankton Expedition, Bd. 2, K. d., p. 16; 1902, 

 Wissen. Ergeb. deutsch. Tiefsee Expedition, Dampfer Valdivia, Bd. 3, Lfg. i, p. 5; J906, Nordisches Plankton, Nr. n, 

 p. 44. — Maas, 1897, Mem. Mus. Comp. Zool. at Harvard College, vol. 23, No. I, pp. 78, 79; 1899, Bull. Soc. Zool. de 

 France, p. 165; 1904, Result Camp. Sci. Prince de Monaco, fasc. 28, p. 48; 1903, Scyphomedusen der Siboga Expedition, 

 Monog. II, p. 14; 1907, Ergeb. und Fortschritte der Zool., Bd. i, p. 195. — Browne, 1908, Trans. Roy. Soc. Edinburgh, 

 vol. 46, p. 240. — BiGELow, H. B., 1909, Mem. Mus. Comp. Zool. at Harvard College, vol. 37, p. 37. 



GENERIC CHARACTERS. 



Coronatse with numerous (9 or more) tentacles and equally numerous marginal sense- 

 organs. Twice as many marginal lappets as sense-organs. 8 adradial gonads and 4 inter- 

 radial subgenital ostia. 4 lips. The tentacles and marginal sense-organs alternate regularly, 

 but the insenions of the tentacles and their pedalia are higher up on the exumbrella than are 

 the insertions of the pedalia of the sense-organs. 



The type species is luyvillei Haeckel. 



Haeckel distinguished "Atolla" with 8 gonads grouped in 4 pairs and "Collaspis" with 

 8 separate, equally spaced gonads. As was first shown by Fewkes, 1886, both of these con- 

 ditions may exist upon one and the same medusa, some of the gonads being paired, others 

 separated by equal spaces. The name "Collaspis" must therefore be dropped, being equiva- 

 lent to Atolla. 



The medusae of this genus are deep-sea forms and are inhabitants of all oceans, and 

 large numbers of them have been taken in open nets dragged at 350 to 2,500 fathoms. A few 

 specimens have also been found upon the surface, but this is unusual. They are often brought 

 up from depths of about 100 fathoms where the ocean is more than 2,000 fathoms deep. 



In the sculpturing of the exumbrella, the structure of the tentacles, the general features 

 of the anatomy of the gastrovascular system, and in the arrangement of the muscular system, 

 these medusa are strikingly similar to Periphylla but differ in the absence of funnel cavities 

 in the floor of the subumbrella and in the flat, discoidal shape of the bell. The central stomach- 

 cavity is thus less complex, but not essentially different from that of Periphylla. 



The details of the structure of gastrovascular system, sense-organs, gonads, etc., are 

 given in the description of A. bandit. 



Ephyroides rotaformis Fewkes, 1886 (Report U. S. Fish Commission for 1884, p. 949), 

 may be closely related to Atolla. The 16 to 32, or more, pedalia are separated by wide intervals 

 instead of by narrow clefts, as in Atolla. Several specimens are mentioned by Fewkes as 

 having been dredged from depths of 389 to 1,555 fathoms in the Gulf Stream off the coast 

 of the United States, but were not sufficiently well preserved to admit of description. 



Vanhoffen, 1902, discovered in Atolla, a system of excretory openings which consists of 

 8 pores, 2 in each principal radius near the perradial angles of the stomach and centripetal 

 to the zone of the gonads, with which this system has no connection. The position of these 

 openings is marked by 8 oval spots upon the floor of the subumbrella. The closely allied 

 EphyropsidcT have numerous openings on the subumbrella at the place of connection between 

 the tentacular canals and the ring-canal, but these have not been observed in Atolla. 



Vanhoffen (1902), Maas (1904,) and Bigelow (1909), have given the best detailed descrip- 

 tion of the genus Atolla. The development is unknown. 



