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



PELAGIC NEMERTEANS. 



There are about 50 pairs of ovaries, each forming 

 a large curved organ, and containing, when fully deve- 

 loped, some 6—8 eggs, which attain a size of no less 

 than 2.5 mm. 



Habitat: 



The type specimen 1 ) was taken east of the Lacca- 

 dives, (Lat. 12° 2' N; long. 73" 46' E) at a depth of 1154 

 fathoms. The implement used was a bottom trawl, the 

 individual was however doubtless taken during the hauling 

 up; both the specimens from the "Michael Sars" are cer- 

 tainly pelagic. These latter were taken at St. 81 (Lat. 

 48° 2' N; long. 39" 55' W) on the 12 h 1910, and St. 64 

 (Lat. 34° 44' N; long. 47°, 52' W) on the 24 /« 1910, depth 

 2000 metres (3000 metres of wire). The horizontal area 

 of distribution is thus extensive, the species having been 

 found both in the Indian Ocean and in the Atlantic. 



Nectonemertidae (Verrill 1892) Brinkmann emend. 



Slender, small to medium sized forms, with 

 almost parallel sides. The body relatively small 

 and only sligtly flattened. The hinder end is 

 shaped into a higly developed caudal fin narrowing 

 at the root. The diverticula of the intestine lack 

 ventral branch. The male, when mature, has a 

 pair of large lateral tentacles a little beyond the 

 fore end. 



Nectonemertes Verrill 1892 (partim). 

 Syn. Hyalonemertes Verrill 1892. 

 Characters of the family. 



Nectonemertes mirabilis Verrill 1892. 

 (Plate II, Figs. 14—22). 



Synonyms: 

 d" N. mirabilis Verrill 1892 (20). 

 N. mirabilis Biirger 1895, 1904, 1905 (3, 4, 5). 

 N. mirabilis Coe 1905 (7). 

 N. Grimaldi Joubin 1904, 1906 (12, 13). 

 N. pelagica Cravens & Heath 1907 (8). 

 N. japonica Foshay 1912 (9). 

 2 Hyalonemertes atlarltica- Verrill 1892 (20). ■■ 

 Hyalonemertes atlantica Burger 1895, 1904, 1905 (3, 4, 5). 

 <f&% Nectonemertes mirabilis Brinkmann 1912, 1915 (1, 2). 



Nectonemertes mirabilis Brinkmann in Murray and Hjort, 1912(18). 

 nnn; N. mirabilis and H. atlantica Burger 1907 (1912) (6). 



From the list of synonyms given above 2 ) it will be 

 seen that my view as to this species differs essentially 



l ) Laidlaw states that this was a male. On examining his sec- 

 tion series, however I found it to be a female with eggs almost mature. 



-) In the preliminary survey of the more prominent species among 

 the material, (in Murray & Hjort p. 577) I mentioned N. lobata Joubin 

 as synonymous with N. mirabilis. Closer investigation subsequently 

 showed this to be erroneous; the form belongs to the genus Balaena- 

 nemertes Biirger (6). 



BRINKMANN — 2 



from those of previous writers. This may be explained 

 by the fact of my having had so large a quantity of 

 material to deal with, comprising no less that 82 spe- 

 cimens from the present expedition alone. 



First of all, with regard to Verrill's two "species", a 

 perusal of the works quoted shows that of N. mirabilis 

 16 specimens are known, all being males, while H. at- 

 lantica is represented by two individuals, both female. 

 The only noteworthy difference Verrill has been able to 

 demonstrate as between the two "species" -- apart from 

 the difference of sex - - is the existence of the two lateral 

 tentacles which characterise the former. An examination 

 of the "Michael Sars" material from this point of view 

 revealed the fact that all specimens with tentacles were 

 male, all others with genital organs so far developed as 

 to be visible through a magnifying glass, being female. 



As long as only 16 and 2 specimens respectively 

 were known, it was of course permissible to regard the 

 peculiar distribution of the sexes as possibly accidental; 

 when, however, the same was found to be the case with 

 the 82 from the „Michael Sars" the accident theory was 

 no longer tenable and another had to be sought. And in 

 my opinion, the true explanation is that we have here 

 to deal with males and females of one and the same 

 species. 



This hypothesis is strongly supported by the fact 

 that the tentacles exhibit a series of gradual stages af 

 developement from young to full-grown specimens (Plate II, 

 Figs. 16 — 22); it is advanced to a certainty by the fact 

 that I have succeeded in demonstrating that the develop- 

 ment of the tentacles progresses simultaneously with that 

 of the testicles. Further confirmation is moreover afforded 

 by the fact that a like secondary sexual difference can be 

 shown to exist in two other species of the same genus. 



N. mirabilis has been very closely investigated by 

 Cravens and Heath; the specimens which they found 

 to differ from' Verrill's first description, and which they 

 therefore placed under the new species N. pelagica have 

 all been found to fall within the range of variability of 

 the present species; the same applies to N. Grimaldi 

 Joubin, as also N. japonica Foshay. 



Thorough demonstration of this will be found in the 

 monograph on pelagic nemerteans by the present writer; 1 ) 

 it will here suffice to indicate the area of distribution of 

 the species, as evidenced by the finds made by the 

 „Michael Sars". 



The specimens of N. mirabilis hitherto known were 

 taken at widely different localities, Verrill found it off the 

 east coast pf North America, Cravens and Heath off the 

 west coast of California, Joubin off the west coast of 

 Europe, while Foshay brought it from Japan. The species 



') Vide Introduction. 



