Kirkegaardia brigitteae Blake, 2016, new species

Kirkegaardia brigitteae new species

Figures 32–33

Monticellina sp. 2: Hilbig 2001: 540; Hilbig et al. 2006: 714–719; Montiel et al. 2015: Appendix 1.

Material examined. Weddell Sea, Halley Bay, R/ V Polarstern, EASIZ II Cruise (ANT-XV/3), Sta. 48-136, 74°33.0′S, 27°13.1′W, 2012 m, 0 9 Feb 1998, multibox corer, coll. B. Ebbe, holotype (ZMH P-27812).— Weddell Sea, Drescher inlet, South of Vestkapp (West Cape), R/ V Polarstern, EASIZ II Cruise (ANT-XV/3), Sta. 48- 0 91, 73°28.4′S, 22°48.8′W, 1510 m, 0 4 Feb 1998, multibox corer, coll. B. Ebbe, 7 paratypes (ZMH P-27807); Sta. 48-093, 73°28.3′S, 22°54.5′W, 1988 m, 0 4 Feb 1998, multibox corer, coll. B. Ebbe, 15+ paratypes, were dry and rehydrated (ZMH P-27808); Sta. 48-131, 73°23.7′S, 22°09.1′W, 1985 m, 0 8 Feb 1998, multibox corer, coll. B. Ebbe, 9 paratypes (ZMH P-27809); Sta. 48-132, 73°20.7′S, 22°18.4′W, 2387 m, 0 8 Feb 1998, multibox corer, coll. B. Ebbe, 7 paratypes (ZMH P-27810). — Powell Basin, SW of South Orkney Islands, R/ V Polarstern, ANDEEP III Cruise (ANT-XXII/3), Sta. 150-3, 61°48.63′S, 47° 27.67′W, 1956 m, 20 Mar 2005, 0.25m 2, box corer, 1 specimen (ZMH P-27813); Sta. 150-8, 61°48.56′S, 47°27.48′W, 1942 m, 20 Mar 2005, multi corer, 1 specimen (ZMH P-27814); 1 specimen SEM (JAB).— Antarctic Peninsula, South Shetland Islands, off King George Island, R/ V Polarstern, EASIZ II Cruise (ANT-XV/3), Sta. 48-330, 61°20.6′S, 58°15.1′W, 2009 m, 18 Mar 1998, multibox corer, coll. B. Ebbe, 1 specimen (JAB).— Bellingshausen Sea, NW Anvers Island, R/ V Polarstern, ANDEEP III Cruise (ANT-XXII/3), Sta. 154-3, 62°31.52′S, 64°39.64′W, 3801 m, 30 Mar 2005, multi corer, 1 specimen (ZMH P-27815).

Description. A moderately sized, threadlike species; none complete, but several posterior fragments appear to belong to the species. Holotype largest specimen, 16 mm long, 0.5 mm wide across thoracic segments and 0.8 mm wide across abdominal segments for 65 setigerous segments. Posterior fragments greatly expanded, up to 3 mm long, 0.8 mm wide with up to 22 segments; these suggest that complete worms would be at least 20 mm long and have 80 or more segments. Body light tan in alcohol with no obvious pigment. Pre-setigerous region elongate, narrow, approximately 2.5x as long as wide (Figs. 32 A–B, 33A–B), as long as first eight setigers of thoracic region on largest specimens. Prostomium short, conical, curved ventrally, tapering to rounded anterior margin (Fig. 32 A– B); eyes absent; nuchal organs narrow slits at posterolateral border. Peristomium elongate, narrow, relatively smooth throughout, lacking distinct lateral grooves (Fig. 32 A–B); anterior one-third to one-half of peristomium with a distinct mid-dorsal ridge continuous with prostomium (Fig. 32 A–B); dorsal surface of remaining peristomium smooth. Transition of peristomium to setigerous segments indistinct, merging smoothly with middorsal channel of thoracic region (Fig. 32 A). Dorsal tentacles arising close together anterior to level of setiger 1; first pair of branchiae lateral to these tentacles (Fig. 32 A–B); second pair of branchiae on posterior dorsal border of setiger 1; subsequent branchiae in similar locations overlying mid-dorsal channel (Fig. 32 A). Most branchiae evident as stubs; branchiae rarely observed in abdominal segments.

Thoracic segments numbering 6–12, smaller specimens with fewest; each thoracic segment short, 3.5x wider than long, parapodia shifted dorsally, overlying a mid-dorsal channel, with narrow ridge along midline of channel (Fig. 32 A). Abdominal segments becoming longer, almost as wide as long (Fig. 32 C), segments narrowing, becoming somewhat moniliform in posterior, last 15 or so segments greatly expanded; pygidial segment with dorsal anus overlying short conical ventral lobe (Fig. 32 D); ventral surface of far posterior segments with low midventral ridge; other regions of body without ventral groove or ridge.

Parapodia of thoracic segments best developed as distinct raised noto- and neuropodial lobes (Fig. 32 A–B), continuing in abdominal segments (Fig. 32 C). Thoracic parapodia shifted dorsally (Fig. 32 B), abdominal parapodia in lateral locations (Fig. 32 C). Setae of thoracic region initially all smooth capillaries transitioning to denticulated setae in last thoracic segments and anterior abdominal segments. Thoracic notosetae numbering 6–8, neurosetae 6– 10 per fascicle, depending on size of worm; abdominal notosetae numbering 4–7 per fascicle, neurosetae 4–7. Notosetae longer, thinner than shorter, thicker neurosetae especially on abdominal segments. Noto- and neurosetae with denticles first present from anteriormost abdominal setigers, 12–14 in largest specimens; denticles larger and more prominent on neurosetae (Fig. 33 E) than on notosetae (Fig. 33 G); notosetae with denticles directed ventrally in fascicles, denticles of neurosetae directed dorsally, vis-à-vis. In light microscopy only the denticles along the cutting edge visible, best seen at 1000x (Fig. 32 E). With SEM large blunt-tipped denticles seen to occur along the cutting edge of each neuroseta, with numerous smaller denticles or thick fibrils occurring lateral to larger denticles (Fig. 33 E–F); notosetae with most denticles on cutting edge of a similar size to lateral denticles (Fig. 33 G).

Methyl Green stain. The peristomium retains an overall diffuse green stain, with a darker posterior dorsal patch developed to variable degrees. The middle and posterior segments of the thoracic region are stained as broad blue bands that encircle each segment up to the border of the mid-dorsal channel but leaving the actual parapodia unstained (Fig. 33 A–C); the stain is an intense dark blue on the last 2–3 thoracic segments (Fig. 33 A). The abdominal segments retain a bright green stain laterally on each parapodium and a mid-ventral spot or short longitudinal band (Fig. 33 D).

Etymology. This species is named for Dr. Brigitte Ebbe, benthic ecologist and polychaete systematist, who collected the majority of these specimens and provided them to me for study. Dr. Ebbe is a long-time colleague and authority on deep-water benthos of Antarctica and elsewhere.

Remarks. Kirkegaardia brigitteae n. sp., a deep-sea Antarctic species, is most closely related morphologically to the type-species of the genus, K. heterochaeta, from shallow subtidal habitats in the Mediterranean Sea. The two species are similar in having a distinct mid-dorsal ridge that extends from the prostomium to part way along the peristomium, leaving the rest of the dorsal peristomial surface smooth; a mid-dorsal thoracic ridge; and similar MG staining patterns. The two species differ in that in K. heterochaeta the mid-dorsal thoracic ridge encompasses the entire dorsal surface of the channel, whereas in K. brigitteae n. sp., there is a separate narrow ridge on the larger dorsal surface within the channel. Further, the peristomium of K. heterochaeta has at least one lateral groove producing two annular rings, whereas K. brigitteae n. sp. has none. The far posterior pre-pygidial segments of K. brigitteae n. sp. include about 15 segments that are greatly expanded, whereas the same segments of K. heterochaeta, although also expanded, are few in number. Although the basic patterns of MG staining reactions are similar, K. heterochaeta has an intense dorsal green stain on the peristomium, whereas K. brigitteae n. sp. has only a weakly staining reaction that de-stains rapidly.

Biology. No specimens were observed to have gametes.

Distribution. Antarctica, Weddell Sea, in slope depths, 1510–2387 m; Powell Basin, 1942–1956 m; South Shetland Islands, 2009 m; Bellingshausen Sea, 3801 m.