ATLANT. DEEP-SEA EXPED. 1910. VOL. Ill] 



SCYPHOMEDUSAE. 



Nausithoe Kolliker. 



During the cruise of the "Michael Sars" two species oi 

 Nausithoe were taken, both apparently new to science. They 

 add many interesting facts to our systematic knowledge 

 of the genus. First of all, they confirm the fact first 

 pointed out by Bigelow 1 ) that the rhopalia of the typical 

 deep-sea inhabitants of the genus are devoid of an ocellus, 

 which is found, however, in the species of Nausithoe 

 inhabiting the surface layers. Bigelow called attention 

 to the absence of an ocellus in N. rubra Vanhoffen and 

 ocelli are also missing in N. atlantica n. sp. and A', globi- 

 fera n. sp. 



The new species are also of great interest because 

 of the position and shape of their gonads; they might 

 both be referred to Haeckel's 2 ) genus Nausicaa. Maas 3 ) 

 has, however, pointed out that N. picta Agassiz and 

 Mayer, in the position of its gonads shows every transitory 

 stage between the typical Nausithoe and Nausicaa; thus 

 Maas in opposition to Vanhoffen 4 ) finds that an inter- 

 radial approximation of the proximal parts of the gonads 

 does take place in the N aus it h o i da e. In the present 

 case we find two species showing a proximal approach 

 of their gonads, and in one of the species this 

 approach sometimes apparently results in a 

 coalescence. 



It is rather surprising that no previously 

 known species of Nausithoe were taken, and 

 especially N. punctata Kolliker, which occurs 

 in several parts of the Atlantic crossed by the 

 "Michael Sars"; the only reasonable explana- 

 tion seems to be that N. punctata is limited 

 to coastal waters, and the "Michael Sars" 

 material includes very few specimens of neritic 

 Medusae. 



species, but the following description will suffice for 

 the recognition of the characteristic species. 



The medusa attains a diameter of at least 28 mm. 

 It is of a dark, yellowish-brown colour, which often be- 

 comes almost black. The surface of the umbrella is 

 smooth. The central disc of the umbrella is sometimes 

 rather flat, sometimes rather arched, the arched disc repre- 

 senting probably the natural state, the flat one being 

 found only in damaged specimens. The furrow separating 

 the central disc from the marginal parts, is not very prom- 

 inent, but we can always trace it, and in the better 

 preserved specimens it is rather distinct. The marginal 

 parts of the medusa on the exumbrellar side are furnished 

 with two rows of pedalia (pi., fig. 1), one row containing 

 the rhopalar, the other the tentacular pedalia. The eight 

 rhopalar pedalia are prominent and almost semi-globular, 

 often a little broader than they are long. The eight ten- 

 tacular pedalia are of the same breadth as the rhopalar 

 ones, but they are about twice as long and not very 

 distinctly circumscribed. The alternation of the short and 

 rather prominent rhopalar pedalia with the long and not 

 very prominent tentacular ones gives the marginal parts 

 of the medusa a peculiar appearance, unlike any previ- 



Nausithoe atlantica n. sp. 

 PI., figs. 1—4. 



At Stat. 56 two specimens were taken at 

 a depth of 500 metres which bear a strong resem- 

 blance to Nausithoe rubra Vanhoffen, but prove 

 on closer examination to be specifically distinct. 

 Later six more specimens were taken in the 

 youngfish trawl from a depth of 500 metres. 

 All the specimens being more or less damaged, 

 it is impossible to give full details of the 



Q'Nausitlwe atlantica 

 A — ..— globifera 



Fig. 5. 



1 ) The Medusae (Mem. Mus. Comp. Zool., Vol. XXX1I1), p. 36. 



2 ) System der Medusen. Jena 1880, p. 485. 



3 ) Die Scyphomedusen der Siboga-Expedition (Siboga Expeditie, Monogr. XI), Leiden 1903, p. 20. 



4 ) Deutsche Tiefsee-Expedition, p. 32. 



