Kirkegaardia carinata, Blake, James A., 2016

Blake, James A., 2016, Kirkegaardia (Polychaeta, Cirratulidae), new name for Monticellina Laubier, preoccupied in the Rhabdocoela, together with new records and descriptions of eight previously known and sixteen new species from the Atlantic, Pacific, and Southern Oceans, Zootaxa 4166 (1), pp. 1-93: 47-50

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Kirkegaardia carinata

new species

Kirkegaardia carinata   new species

Figures 23–24 View FIGURE 23 View FIGURE 24

Monticellina   sp. 3: Blake et al. 2009: 1796.

Material examined. California continental slope west of the Farallon Islands, San Francisco Deep Ocean Disposal Site (SF-DODS): 2003 monitoring survey, R/ V Point Sur, Sta. 116, 37º35.080′N, 123º29.039′W, 2908 m GoogleMaps   , 13 July 2007, coll. J.A. Blake, holotype (LACM-AHF Poly 8928); Sta. 23, 37º36.860′N, 123º28.850′W, 24 September 2003, 2821 m, coll. J.A. Blake, 1 paratype (LACM-AHF Poly 8924); 2006 monitoring survey, R/V Point Sur, Sta. 64, 37º35.968′N, 123º32.989′W, 3145 m, 27 September 2006, coll. J.A. Blake, 1 paratype (LACM- AHF Poly 8925); Sta. DR2A, 37°22.924′N, 124°01.001′W, 3775 m, 29 July 2006, coll. J.A. Blake, 1 paratype (LACM-AHF Poly 8926); 2007 monitoring survey, R/V Point Sur, Sta. 19, 37º38.166′N, 123º30.213′W, 3100 m, 11 July 2007, 1 paratype (LACM-AHF Poly 8927); Sta. DR3A, 37°17.537′N, 124°09.192′W, 3864 m, 13 July 2007, 1 specimen, coll. J.A. Blake (JAB).

Description. An elongate, narrow-bodied species, all specimens incomplete. Holotype mostly complete, 17 mm long, 0.5 mm wide across thoracic region, with 71 setigerous segments; paratypes smaller, with fewer segments; length and number of setigerous segments variable, age dependent. Thoracic region with 10–12 setigerous segments, with slender, less mature specimens having fewest. Thoracic segments about 2x as wide as long ( Figs. 23 View FIGURE 23 A, 24A–B), transitioning to anterior abdominal segments only slightly wider than long with segmental boundaries indistinct ( Figs. 23 View FIGURE 23 C, 24C); middle and posterior segments becoming oval, but not moniliform; no ventral grooves or ridges present; thin ventral line evident along abdominal segments, not a raised ridge.

Pre-setigerous region about 1.8x as long as wide. Prostomium conical, tapering to narrow rounded apex ( Figs. 23 View FIGURE 23 A–B, 24A–B); eyes absent; slit-like nuchal organs present on posterior lateral margins ( Fig. 23 View FIGURE 23 B). Peristomium smooth without obvious annulations, dorsal surface raised, but without an obvious crest ( Figs. 23 View FIGURE 23 A–B, 24A–B), peristomium merging posteriorly with raised mid-dorsal ridge of thoracic region ( Fig. 23 View FIGURE 23 A). Dorsal tentacles arising on posterior margin of peristomium, with first pair of branchiae posterolateral to tentacles in notch between peristomium and setiger 1 ( Fig. 23 View FIGURE 23 A–B); second pair of branchiae on posterior margin of setiger one dorsal to notosetae and on edge of mid-dorsal channel ( Fig. 23 View FIGURE 23 A); subsequent thoracic branchiae in similar location; anterior abdominal branchiae, when present dorsal to notosetae, but not in as dorsal a position because parapodia shift laterally; no branchiae observed in middle and posterior segments.

Parapodia of thoracic region elevated above dorsal midline, producing shallow mid-dorsal channel or groove between parapodia ( Fig. 23 View FIGURE 23 A); this channel with narrow elevated ridge or keel continuing to end of thoracic region; ridge broken into elevated lobes in last 2–3 thoracic segments ( Fig. 23 View FIGURE 23 A).

Parapodia well-developed throughout, with short triangular-shaped podial lobes in thoracic region and broad membranous parapodia in abdominal segments ( Fig. 23 View FIGURE 23 A); abdominal parapodia surrounded by dark glandular tissue that retains MG stain imparting distinctive pattern along entire body ( Fig. 24 View FIGURE 24 C, see below). Thoracic setae consisting of 11–12 long simple capillaries per notopodium and 8–10 similar setae per neuropodium; anterior abdominal setae similar with neurosetae becoming shorter, wider basally, and with minute denticles along one edge from setigers 16–17 on holotype visible at 400– 1000x ( Fig. 23 View FIGURE 23 E); notosetae also developing denticles along one edge from setigers 17–18 on holotype ( Fig. 23 View FIGURE 23 D). Notosetae numbering 5–6 per notopodium in anterior abdominal parapodia and 4–5 in posterior parapodia; neurosetae shorter and broader than notosetae, numbering up to 10 per neuropodium in anterior abdominal segments and 4–5 in posterior abdominal segments. Noto- and neurosetae of abdominal segments with fine denticles or teeth along one margin ( Fig. 21 View FIGURE 21 D–E). Notosetae with denticles directed ventrally and denticles of neurosetae directed dorsally, vis-à-vis.

Nature of posterior end and pygidium not known.

Methyl Green stain. Kirkegaardia carinata   n. sp. has a distinctive MG staining pattern, with the holotype having a mid-dorsal elongate oval patch on the peristomium that extends somewhat laterally ( Fig. 24 View FIGURE 24 A–B); the venter of thoracic region has dark-blue-staining segmental bands that extend dorsally to the mid-dorsal ridge ( Fig. 24 View FIGURE 24 A–B); the parapodia of abdominal segments stain heavily producing lateral lines along each segment ( Fig. 24 View FIGURE 24 C).

Etymology. The species name, carinata   is from the Latin carina, a keel, referring to the mid-dorsal ridge that is within the channel between the parapodia of the thoracic region of this species.

Remarks. Kirkegaardia carinata   n. sp. is another species in the group of 12 species that have the thoracic parapodia elevated over a mid-thoracic channel. Of these 12 species, K. carinata   n. sp. is most similar in morphology to K. dorsobranchialis   , K. chilensis   n. sp., and K. cryptica   in having an entirely smooth peristomium with no dorsal ridge. Of these, K. carinata   n. sp. and K. chilensis   n. sp. have a prominent mid-dorsal ridge within the dorsal channel on the thorax that is lacking in both K. dorsobranchialis   and K. cryptica   . K. carinata   n. sp. differs from K. chilensis   n. sp. in having a distinctively rich MG staining pattern on the peristomium, thoracic region, and the abdominal parapodia whereas a MG pattern is largely absent on K. chilensis   n. sp. except for weak retention on the thoracic segments. In addition, the mid-ventral segments of the thoracic region of K. chilensis   n. sp. are expanded whereas the thoracic segments of K. carinata   n. sp. are all of the same size.

Biology. A rare species, K. carinata   n. sp. is limited to lower continental slope and abyssal depths in soft muddy sediments. Some paratypes partially covered with thin crust of silt particles, suggesting a thin sediment tube may be present.

Distribution. Lower continental slope and continental rise off northern California, 2821–3864 m.