Comprehensive Description

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Eusamytha sexdentata, new species


(Plate 46)



Record: 12:24 sta. 995 (4, TYPE).



Description: All specimens are in long, cylindrical, silt-covered tubes from which they are removed with parapodia and setae closely appressed to the body. Length of a nearly complete specimen is 28 mm, and width in the postbranchial or widest region is 1.08 mm. Segments include 15 thoracic and 15 abdominal with setae. Paleae are present and conspicuous (Fig. A); they form a fan-shaped fascicle at the outer bases of the branchiae. The prostomium is shovel-shaped, trilobed, and has a median lobe slightly set off from the larger lateral lobes by narrow grooves; eyes are lacking; its frontal margin is nearly straight except for a longer, pro­jecting median lobe.


The oral cavity, laid bare by dissection, is filled by a broad, folded membrane with a straight free margin; it lies over a smooth, thick, transverse, fleshy membrane resembling a lower lip but lying immediately over it.


Branchiae, numbering three pairs, are inserted on a raised membrane behind the prostomium. The dorsalmost pair is basally separated by a narrow space (Fig. B); the second and third pairs are successively more ventral, and all are long, smooth, tapering distally, and directed forward (fixed in the tube).


The paleal segment exceeds in size the segment immediately follow­ing. Each fascicle has about 18 long, distally curved spines in which the base is cylindrical and the distal curved part is thin and knifelike (Fig. C). The first normal setiger is smallest and located immediately behind and within the paleal fascicle. The second is much larger, and the third setigerous segment has a dorsal crest, best seen in lateral view (Fig. A). The fourth setigerous segment is the first uncinigerous. The presence of a dorsal crest allies the genus with the subfamily Melinninae but the species lacks the modified fine setae of anteriormost segments which char­acterize this subfamily.


Notosetae are numerous, long, slender and distally pointed. Thor­acic uncini are platelike ; each has about six teeth in a single row along the cutting edge (Fig. D).


The body cavity contains large, though not mature, ova. Nephridial papillae are present in anterior segments. The tube is long, cylindrical, measures to 100 mm long by 3.5 mm wide at the distal end; it is ex­ternally covered with brown silt and clay.


Distribution: Limited to Bransfield Strait, in 2119-2562 m.”



(Hartman, 1967)


Creative Commons Attribution Non Commercial 3.0 (CC BY-NC 3.0)

© National Museum of Natural History, Smithsonian Institution

Source: Antarctic Invertebrates Website (NMNH)

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