114 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.15 



Nephtys acrochaeta, new species 

 Plate 16, figs. 1-6 



Material examined. — Holotype specimen from off Uruguay, South 

 America, Swedish State Museum, Stockholm, Sweden. 



A single specimen, posteriorly not quite complete, consists of 58 

 segments and measures 50 mm long and 1.75 mm wide without, 3 mm 

 with parapodia at the widest region or about segment 16. The body has 

 no color pattern but is pale tan throughout. The prostomium is quadrate, 

 a little longer than wide (proboscis retracted) ; its anterior margin is 

 straight, its sides about parallel, and the posterior margin merges imper- 

 ceptibly into the first segment. The anterior frontal antennae are small, 

 located at the anteroectal margins and continuous with the prostomium. 

 The posterior antennae are much larger and located immediately behind 

 and ventral to the frontal antennae; they are triangular with a broad 

 base. Nuchal organs are conspicuous papillar processes at the postectal 

 margins of the prostomium. There are no eyespots. The ventral folds of 

 the lower lip are deeply longitudinally grooved so as to extend back 

 onto the seventh segment (proboscis retracted). 



The proboscis, seen by dissection, has 21 rows of bifid terminal 

 papillae and about as many rows of subterminal papillae. There is none 

 distinctly middorsal or midventral. The distalmost are about as large 

 as the terminal papillae and those more proximal gradually decrease in 

 size. Those in the 2 or 3 distalmost rows are larger than the others; 

 they are then replaced by 14 longitudinal rows of increasingly smaller 

 papillae in 7 to 9 rows after which they disappear. The proximal sur- 

 face of the proboscis is smooth. The pharyngeal jaws are translucent 

 light horny brown with a sharp distal tooth, a quadrate base and 4 angled 

 ridges that extend from the tip to the base. 



Interramal cirri are first present from the ninth segment as a small 

 filament; they increase gradually in size and are recurved from segment 

 12 though still small and slender; maximum development is not attained 

 until near the midle of the body where a complete spiral is inscribed (fig. 

 1 ) ; interramal cirri are continued back at least through 59 segments 

 (end of the specimen). 



On the dorsal and ventral sides of the body, the lateral margins of 

 the epidermis are laterally prolonged to form scale-like folds that ex- 

 tend back onto the succeeding segments, thus appearing imbricated ; this 

 character is notable in Nephtys squamosa Ehlers (see above) but not so 

 conspicuously developed in N. acrochaeta. 



