EUNICIDAE 



123 



Genus Nicidion, Kinberg 



Nicidion kinbergii, Webster. 



Webster, 1884, p. 320, pi. xii, figs. 81-88. 



Treadwell, 1921, p. 91, pi. vi, figs. 5-8, text-figs. 324-332. 



St. I. 16. xi. 25. Clarence Bay, Ascension Island. 7^ 55' 15" S, 14° 25' 00" W. 16-27 m. 

 Gear NRM. Bottom: coral, sand and shell. Two specimens. 



mmT 



O 



Remarks. The largest of the two incomplete speci- 

 mens measures 13 mm. by i mm. including the feet 

 and has about 65 chaetigers. The colour in spirit is 

 a pale brown. The prostomium is deeply incised in 

 front and the tentacles are short, the median, which 

 is the longest, barely reaching to the 2nd chaetiger. 

 The tentacular cirri are so small as easily to be 

 overlooked . 



The flattened area of the body with the short 

 crowded segments extends from about the 5th to the 

 40th segments, about ten segments further back than 

 in Crossland's (1904, p. 327) Nicidion gracilis. More- 

 over, the change over to the longer and more arched 

 condition of the posterior somites is much more 

 gradual than as recorded by Crossland for his species. 



For the first five feet, there is a stout dorsal cirrus 

 reaching to the tips of the bristles, and a stout conical 

 ventral cirrus. By the loth chaetiger the dorsal cirrus 

 is much reduced and the ventral cirrus is a conical projection on top of a glandular 

 pad. By the 25th the dorsal cirrus is still further reduced in size and the ventral cirrus 

 is a mere button. At the 50th chaetiger the dorsal cirrus is a slight digitiform process 

 as in the 25th foot and the ventral cirrus is again a small conical process. 



The bristles agree with those figured by Treadwell. At about the 35th chaetiger the 

 bidentate acicular chaeta appears, and at the same time the yellow aciculum gives place 

 to a stouter black aciculum. 



The dental formula (Fig. 43) is 5 — 5 : 5 + 4 — 6. Details of the jaws are given in 

 the figure. 



A'^. gracilis, Crossland, A^. brevis, Ehlers (1887, p. 98), and the present species are 

 all closely allied. In addition to the diflrerences between A^. gracilis and A^. kinbergii 

 already mentioned, Crossland makes no reference to the winged type of capillary bristle 

 such as is present in Webster's species. 



Ehlers' N. brevis from Key West has slightly different upper jaws and the secondary 

 lateral supports to the lower jaws figured by Ehlers (PI. xxix, fig. 2) are absent from the 

 present species. 



Fig. 43. Nicidion kinbergii. 

 Upper jaws. 



l6-2 



