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



PELAGIC NEMERTEANS. 



the intestine in a single row on either side of the pro- 

 boscis sheath, commencing in the cascal region. The ovaries 

 open to the exterior on the outer side of the lateral 

 nerve. A considerable number of eggs are developed in 

 each of the ovaries. 



Habitat; St. 92 (Lat. 48° 29' N; long 13° 55' W.) 

 - 3 — 2i h, 2000 metres depth (3000 metres of wire). 1 ) 



Plotonemertes nov. gen. 



Forepart of the body thickened to a club-shape. 

 Mouth and proboscis pore separate. Muscles fol- 

 lowing the lateral nerve lacking. The male has a 

 large double integumental glandular organ on the 

 under side of the tail. 



Plotonemertes adhserens nov. sp. 

 (Plate I, Figs. 9—10.) 



This species is likewise based upon a single speci- 

 men. As will be seen from Fig. 9, the shape of the body 

 differs from that in Bathynemertes by the club-shaped 

 thickening of the forepart; the proboscis is unusually thick, 

 owing to the presence of a highly developed exterior 

 basement layer, a character which renders the species 

 easily distinguishable. The male is further easily recog- 

 nised by the large double integumental glandular organ 

 on the under side of the tail, some idea of which may 

 be obtained from Fig. 10. Judging from the structure 

 of the organ it can be pushed out, and the enormous 

 glandular apparatus would appear to indicate that it is 

 an adhesive organ, probably used to grip the female 

 during fecundation. 



The species is somewhat smaller than Bathynemertes, 

 length 30 mm., greatest breadth 9 mm., greatest thick- 

 ness 4 mm. 



The muscle layers of the body wall are highly reduced, 

 this being especially the case with the circular layers, 

 but the longitudinal musculature is also very thin laterally. 



The mouth opening lies very close to the terminal 

 proboscis pore, being however distinctly separated from 

 it. Oesophagus lacking. Stomach well developed, its 

 length together with that of the pyloric tube making in 

 all 4.75 mm. The intestine narrow but furnished with 

 over 50 pairs of large and highly ramificated diverticula. 

 The well-developed intestinal caecum has 6 pairs of 

 diverticula. 



The proboscis is more than twice as long as the 

 animal itself; its maximal thickness is about 2 mm. In its 

 wall are 27 proboscideal nerves; the stylet apparatus 

 developed as in Bathynemertes. The proboscis sheath is 

 likewise similar in structure to that of the species men- 



') The question of depth as estimated from length of wire is 

 further discussed on p. 10. 



tioned, but does not extend to the hindmost quarter of 

 the body. 



Save for the lack of metamerical commissures bet- 

 ween the lateral and the dorso-median vessel, the vascular 

 system exhibits but one peculiartty, a short, median vessel 

 extending from the dorsal anastomose of the lateral vessels 

 in the tail, into which the dorso-median vessel opens, 

 out to the extreme point of the tail. 



The lateral nerves are connected by numerous ventral 

 transverse anastomoses. 



The specimen in question is a young male. The 

 testicles form an almost regular row in the head on either 

 side of the proboscis sheath; the one row contained 8, 

 the other 11, opening ventrally. 



Habitat; St. 80 (Lat. 47° 34' N; long. 43 u 11' W.) 

 u h, 2000 metres depth (3000 metres of wire). 



Pendonemertes nov. gen. 



Body thickening to a club-shape at the fore 

 end, the hinder end somewhat applanated. Mouth 

 and proboscis pore separate. Muscles following 

 the lateral nerve well developed 1 ). The proboscis 

 sheath does not extend to the rear half of the 

 body. Only few eggs are developed in the ovaries. 



Pendonemertes Levinseni nov. sp. 

 (Plate I, Fig. 4). 



The "Michael Sars" expedition brought home two 

 specimens of this form, which is of especial interest, 

 since the species - - or at any rate the genus to which 

 it belongs - must be regarded as the original form of 

 a closely related series, the families of Pelagonemertidce 

 and Artnaueriidce. 



The shape of the body is still but very slightly dif- 

 ferent from the Drepanophorus species of the bottom; 

 the fore part is almost circular in section, the hinder end 

 somewhat flattened, though not forming any caudal fin. 



The dimensions of the two specimens were as follows: 

 Length. Greatest breadth. Greatest thickness. Length of prob. sheath. 

 I 26 mm. 6 4 13 



II 20 „ 5 3.5 11 



The musculature of the body wall is here also highly 

 reduced, even the longitudinal muscle layer being later- 

 ally almost entirely lacking. 



The stomach is well developed, leading close behind 

 the brain into the pyloric tube, the two sections together 

 making up a length of 3.6 mm. 



The intestine has between 30 and 40 pairs of diver- 

 ticula; here again they are, with the exception of the 



J ) These muscles were first designed by Burger (6) under the 

 name of "Seitenstammuskel" as found by him in Balaenanemertes 

 chuni. 



