Scoloplos sparsaciculus new species

Figures 15–16

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Material examined. South China Sea, off Brunei, Island of Borneo, Site CA1, R / V Emma, coll. J.A. Blake, box corer, Sta. 50, 2 Jun 2011, 5°42.932′N, 114°12.392′E, 1214 m, holotype (MCZ 153591); Sta. 41, 3 Jun 2011 ,

5°43.452′N, 114°11.302′E, 1268 m, 1 paratype (MCZ 153592); Sta. 11, 6 Jun 2011, 5°50.464′N, 114°10.949′E, 1405 m, 2 specimens (MCZ 153593); Sta. 36, 3 Jun 2011, 5°46.07′N, 114°12.158′E, 1313 m, 1 specimen (MCZ 153594); Sta. 39, 3 Jun 2011, 5°41.492′N, 114°07.681′E, 1443 m, 1 specimen (MCZ 153595); Sta. 44, 2 Jun 2011, 5°47.387′N, 114°15.605′E, 1294 m, 1 specimen (MCZ 153596); Sta. 48, 2 Jun 2011, 5°45.482′N, 114°15.391′E, 1219 m, 1 specimen (MCZ 153597); Sta. 61, 31 May 2011, 5°40.548′N, 114°13.261′E, 1050 m, 1 specimen (UBD).— Site CA2, R / V Emma, coll. P.A. Neubert, box corer, Sta. DA 3, 3 Jul 2011 , 5°25.251′N, 113°29.509′E, 1772 m, 3 paratypes (MCZ 153598); Sta. JA1, 30 Jun 2011, 5°28.376′N, 113°36.642′E, 1888 m, 1 specimen MCZ 153599); Sta. JA4, 30 Jun 2011, 5°30.906′N, 113°37.352′E, 1967 m, 1 paratype (MCZ 153600); Sta. JA6, 30 Jun 2011, 5°31.035′N, 113°36.46′E, 1999 m, 1 specimen (MCZ 153601); Sta. ME5, 25 Jun 2011, 5°18.475′N, 113°33.071′E, 1572 m, 1 specimen (MCZ 153602); Sta. SE2, 29 Jun 2011, 5°31.362′N, 113°42.309′E, 1955 m, 1 specimen (MCZ 153603); Sta. SE5, 28 Jun 2011, 5°35.739′N, 113°47.115′E, 1947 m, 1 specimen (MCZ 153604); Sta. TA4, 2 Jul 2011, 5°26.28′N, 113°26.45.6′E, 1954 m, 1 specimen (UBD) .

Description. All specimens incomplete, most small, less than 3 mm long. Holotype with 56 setigers, 13.7 mm long, 0.4 mm wide across thoracic setigers; paratype from Sta. 41 (MCZ 153592), with 54 setigers, 7.85 mm long, 0.38 mm wide across thorax. All specimens with elongate, narrow bodies (Figs. 15A, 16A), cylindrical in cross section. Most with thoracic and anterior setigers well preserved and intact; posterior segments variable, often with podial lobes and setae damaged. With 9–12 thoracic segments, actual number size related. Thoracic segments narrow, but only about 2.5 times wider than long (Fig. 15A); abdominal segments longer, about twice as long as wide. Color in alcohol: light tan.

Pre-setiger region triangular (Figs. 15A, 16 A–B). Prostomium conical, narrowing to rounded tip; nuchal organs oval openings on posterior lateral margin (Figs. 15A, 16B); eyespots absent. Peristomium about 1½ times longer than first setiger, with one smooth annular ring (Fig. 15A). Proboscis with 2–3 thin lobes when everted.

Thoracic notopodia swollen with a digitiform postsetal lamella (Fig. 15B), short at first, then becoming long, narrow in posterior thoracic segments (Fig. 15A). Thoracic neuropodia similar, with postsetal lamella shorter, thick- er (Figs. 15B, 16C). Transition to abdominal segments abrupt, with fewer noto- and neurosetae. Thoracic notopodia transitioning in abdomen to short, triangular setal lobe with a long, narrow, finger-like postsetal lamella, often with a swollen or bulbous apex (Fig. 15C). A short interramal process present on a few anterior and middle abdominal setigers (Fig. 15C). Neuropodia elongate, thickened, rounded apically with short, narrow ventral cirrus (Figs. 15C, 16E); narrow subpodial flange present ventral to neuropodium followed by short subpodial papillate lobe (Fig. 15C), sometimes paired in a few transitional setigers. Subpodial papillae not observed on smallest specimens.

Branchiae from last thoracic setiger or an anterior abdominal setiger, usually from setiger 11–14, short at first (Fig. 15A), becoming longer, tapering, sometimes asymmetrical, with subapical enlargement (Fig. 15C).

Thoracic notosetae numerous thick, camerated or bristled capillaries arranged in 3–4 rows. Thoracic neurosetae with about 3–4 rows of similar camerated capillaries (Fig. 16 C–D), with posterior row also containing 1–3, rarely 4, inconspicuous uncini (Figs. 15B, 16 C–D). Individual uncini with smooth shafts and two rows of small barbs or camerations along one side (Figs. 15D, 16 C–D), tapering to narrow pointed tip; camerations not visible in some views (Fig. 15E). Abdominal notosetae thin, camerated capillaries. Abdominal neurosetae with 2–3 thin capillaries and a single curved acicula, sometimes protruding, with rounded tip (Fig. 15C). Furcate and flail setae not observed.

Pygidium not observed.

Methyl Green stain. Prostomium not staining, rest of body stains uniformly with no pattern.

Remarks. Comparative comments for S. sparsaciculus n. sp. and the closely related S. californiensis n. sp. are discussed in the Remarks section for the latter species (above). Scoloplos sparsaciculus n. sp. and S. californiensis n. sp. both have only a few uncini in thoracic neuropodia. Most species of the genus recorded from the Pacific have two or more rows of uncini that are mixed with numerous longer capillaries (Hartman, 1957). In addition, both species have a subpodial flange and one or two subpodial lobes ventral to the neuropodium in anterior and some middle abdominal setigers.

Scoloplos sparsaciculus n. sp. is similar to S. intermedius (Hartman, 1965) from slope depths off New England in having 12 thoracic setigers, branchiae from setiger 11, and a subpodial flange and subpodial papillae in abdominal neuropodia. S. intermedius, however, has an interramal cirrus on anterior abdominal parapodia (Hartman, 1965; Mackie 1987); an interramal process is also present on a few anterior abdominal segments of S. sparsaciculus n. sp. but this is low, inconspicuous and not always observed. The two species differ most conspicuously in that the tip of the shaft of some thoracic neuropodial uncini of S. intermedius has an apical hood, and furcate setae are present in abdominal notopodia; in contrast, S. sparsaciculus n. sp. has no hood on the tip of thoracic neuropodial uncini and furcate setae are entirely absent. Scoloplos intermedius is being redescribed in another paper dealing with U.S. Atlantic deep-water orbiniids (Blake, in preparation).

Etymology. The epithet is from the Latin sparsus for few, and acicula for small pin or needle, referring to the reduced number of acicular spines or uncini found in thoracic neuropodia of this species.

Distribution. South China Sea, off Brunei, Island of Borneo, 1219–1955 m.