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



PELAGIC NEMERTEANS. 



intervals. Ramification of the diverticula altog- 

 ether extreme. The muscle layers of the proboscis 

 sheath are arranged in an inner layer of circular, 

 and an outer one of longitudinal fibres. 



Biirgeriella nov. gen. 

 Characters of family. 



Burgeriella notabilis n. sp. 



(Plate I, Figs. 6—7.) 



It has been found necessary to institute a new family 

 for this highly peculiar form, of which unfortunately only 

 a single specimen (male) is known ; it is doubtless derived 

 from forms such as the Planktonemertidce, but cannot be 

 included in this group, differing therefrom in particular as 

 regards the structure of the intestine and of the proboscis 

 sheath. 



Unfortunately, nothing is known as to the appearance 

 of the animal in a living state: judging from that of the 

 specimen preserved in formalin, however (Plate I, Fig. 6) 

 it would seem likely that it is then quite transparent, which 

 would render the intestine even more conspicous. From 

 the habitus figure it will be seen that the extreme and 

 remarkable ramification of the intestine renders this form 

 immediately distinguishable from all other nemerteans. 



Biirgeriella is a very imposing form among pelagic 

 nemerteans, and is in point of size only surpassed by 

 species of the genus Dinoneinertes. 



Length 52 mm. greatest breadth 15 mm. greatest 

 thickness 4 mm. 



The muscular layers of the body wall are thin, the 

 parenchyma however, being highly developed. 



The mouth and proboscis pore are distinctly separate. 

 CEsophagus lacking. The stomach remarkably short, narrow 

 and capable of only slight expansion; at a distance of 

 only 1 mm. behind the mouth-opening it leads into a 

 narrow pyloric tube about 6 mm. long. 



The intestine is narrow, and furnished at intervals 

 with slender but highly ramified diverticula; here also 

 the ramification proceeds from a dorsal and a ventral 

 main branch; these secondary ramifications however, dif- 

 fer from those observed in other nemerteans in being- 

 long, slender, and frequently branching off again. The 

 diverticula being placed at relatively considerable distance 

 one from another, they are further developed to a high 

 degree of ramification on their anterior and posterior 

 surfaces, so that each diverticulum forms a large arboriform 

 appendix to the intestine, not, however, extending so far 

 as to occasion any interweaving of the branches with 

 those from the adjacent stems. 



The intestinal caecum is furnished with 6 pairs of 

 diverticula, which are ramified in the same manner as the 



remaining diverticula, but are, however, somewhat smaller 

 than these. (Plate I, Fig. 7). 



The proboscis is slightly longer than the body. The 

 stylet apparatus does not differ from the type commonly 

 found among pelagic nemerteans. 21 proboscideal nerves 

 are developed. 



The proboscis sheath terminates 5 mm. from the hin- 

 der end; its wall is comparatively thin, and the structure 

 different from that found in all other pelagic nemerteans, 

 inasmuch as the layer of circular muscle fibres is situate 

 on the inner side of the longitudinal layer. 



The lateral nerve stems extend far into the paren- 

 chyma, lying between the dorsal and ventral branch of 

 the intestinal diverticula. Beneath the intestine they form 

 strong transverse anastomoses in the parenchyma, in ad- 

 dition to which several transverse anastomoses were found 

 dorsally and ventrally between the circular and longi- 

 tudinal muscle layers of the body wall, originating in 

 nerve branches from the lateral nerves. 



At the fore end of the body, 6 pairs of testicles are 

 developed (Plate I, Fig. 7), and are here not arranged 

 metamerically, but more or less displaced, the testicular 

 region being, approximately shaped like a horse-shoe. 



The discharge ducts are of greatly varying length, 

 leading to external apertures roughly arranged in two 

 groups close behind the brain; only the apertures from 

 the hindmost testicles are somewhat nearer the caudal 

 region. The testicular wall contains a layer of circular 

 musculature. 



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

 23 — 2 Vt, depth abt. 1333 metres (2000 metres of wire). 



Dinonemertidae nov. fam. 

 Pelagic nemerteans of frequently considerable 

 size. Body broad and flattened. A caudal fin is 

 developed by extreme flattening of the tail. Mouth 

 and proboscis pore distinctly separate. The diverti- 

 cula of the intestine very numerous, with but little 

 or no ramification; the ventral branch always rudi- 

 mentary or altogether lacking. Testicles in two 

 single rows in the head, at times greatly reduced 

 in number. 



Dinoneinertes Laidlaw 1906. 

 Large species. Body broad and flattened, but 

 relatively thick owing to high developement of 

 the parenchyma. Mouth opening situate in front 

 of brain. The diverticula of the intestine vithout 

 lateral ramification. The brain centrally situated. 

 The proboscis sheath does not extend into the 

 rear third of the body. The muscle layers in the 

 wall of the proboscis sheath separate, not inter- 

 woven. 



