Family Maldanidae Malmgren, 1867
Subfamily Nicomachinae Arwidsson, 1906
Genus Nicomache Malmgren, 1865
Subgenus Loxochona Arwidsson, 1906
sp. nov. (Figs. 2, 3, 4; Table 1)
Loki’s Castle vent field, Arctic mid-ocean ridge, 73°33.97′N 08°09.51′E, 2,350 m depth.
Type locality from sedimentary area with low-temperature diffuse venting with barite chimneys, R/V “G.O. Sars” H2DEEP cruise 2009 sample ROV-8, 07 August 2009, fixed in 96% alcohol: Holotype (ZMBN 86266) and 10 paratypes, all complete specimens (ZMBN 86267–86269, 86271–86272, 86274, 86276–86279).
Type locality from chimney walls near the base of black smokers: R/V “G.O. Sars” BIODEEP cruise 2008, sample ROV-11, 14 July 2008, fixed in 96% alcohol: 1 spm. (ZMBN 86283); 1 spm. (ZMBN 86284) and 14 spms (ZMBN 86285). Type locality from sedimentary area with low-temperature diffuse venting with barite chimneys: R/V “G.O. Sars” H2DEEP cruise 2009, sample ROV-8, 07 August 2009, fixed in 96% alcohol: 1 spm. (ZMBN 86267); 1 spm. (ZMBN 86270); 2 spms (ZMBN 86273); 4 spms (ZMBN 86275); 10 spms (ZMBN 86280); 4 spms (ZMBN 86281) and 1 spm. (ZMBN 86282). R/V “G.O. Sars” CGB DEEP cruise 2010: Sample ROV-04, 15 July 2010, fixed in 6% formaldehyde and preserved in 80% alcohol: 3 spms (ZMBN 86286); 6 spms (ZMBN 86287); 20 spms (ZMBN 86288); several spms in block of tubes (ZMBN 86289). Sample ROV-05, 16 July 2010, fixed in 96% alcohol: 7 spms (ZMBN 86290). Sample ROV-09, 18 July 2010, fixed in 96% alcohol: 2 spms (ZMBN 86291).
A large species, up to 125 mm long and 1.8 mm wide, for 22–25 setigerous segments. Asetous preanal segments absent, Pygidial funnel asymmetric, with anal opening ventrally inside anal funnel. First three setigers with 1–2 (3) straight neuropodial spine(s). From setiger four, neurosetae as rostrate hooks; up to 20 hooks in mid-body setigers. Hooks with maximum four apical teeth above main fang and several subrostral hairs. Spiral notosetae absent. 3–4 pairs of nephridial papillae, starting on setiger 7 or 8.
CO1 sequences (DNA barcodes): ZMBN 86269, paratype (Genbank accession nr FR877579) and ZMBN 86270 (Genbank accession nr FR877578).
Body long, cylindrical with asetigerous head, 22–25 setigerous segments and pygidial funnel. Holotype 100 mm long and 1.2 mm wide, with 23 setigerous segments. Paratypes 22–125 mm long and 0.5–1.8 mm wide (Table 1). Prostomium and peristomium fused to form a well-defined head, about 1.5–2 times longer than wide, anteriorly rounded, with wide anterior part (prostomial palpode) (Fig. 2b, c). Cephalic keel well defined, arched. Paired nuchal grooves moderately long, on each side of cephalic keel; posterior part of nuchal grooves parallel, anterior part curving laterally (Fig. 2b). Ocelli not observed. Mouth large, oval, with thick lower lip. Transverse epidermal furrow presents ventrally and laterally slightly posterior to mouth. Dissection of head revealed a foregut with well-developed ventral pharynx and dorso-lateral folds.
Anterior seven setigers with swollen anterior margin. Segmental borders distinct in anterior and posterior setigers and indistinct in middle setigers, from about setigers 8–14. Anterior 6 setigers all relatively short, about 1–2 times as long as wide (Fig. 2a). Setiger seven longer, about 2–3 times as long as wide. Length of setigers 8–9 uncertain due to indistinct segmental borders, but setiger 8 probably short and setiger 9 comparatively long. Setiger 10 and following setigers four times as long as wide or longer. Posterior setigers progressively shorter, with last 1–2 setigers shorter than wide. Parapodia located on anterior half of segments in setigers 1–8, and near posterior end of setiger 9 and remaining setigers.
Pygidial funnel slightly shorter than wide and asymmetrical, with ventral part longer than dorsal part and somewhat curved outward (Fig. 2d). Posterior rim of pygidium with 20–30 small cirri/papillae (Table 1), exceptionally up to 38 (ZMBN 86280), some of which are bilobed. Mid-ventral cirrus absent. Base of pygidium oblique, with dorsal part of pygidial funnel deeper than ventral part (indicated by stippled line in Fig. 2d). Anus situated ventrally inside pygidial funnel. Base of anal funnel with longitudinal folds from pygidial rim towards anal opening; each fold with several small papillae. Anal valve absent.
Distribution of glandular tissue characteristic and well stained by methyl blue. Head uniformly stained, except for the nuchal organs. First nine setigers with complete band anteriorly; staining less distinct dorsally in setigers 7–9. Remaining setigers with staining restricted to parapodia and, in posterior setigers, a narrow transverse band dorsally between the parapodia. Pygidial funnel uniformly stained.
All setigers biramous. Setigers 1–3 with comparatively small noto- and neuropodia. Mid-body and posterior setigers with well-developed notopodial lobes and neuropodial tori. Posterior setigers distinctly swollen at level of parapodia. Anterior setigers with notosetae in single row. From setiger 4, notosetae arranged in double rows. Notosetal rows in dorso-ventral direction in all setigers. All notosetae simple winged capillaries (Fig. 3a, b); capillaries from anterior row shorter and more slender than capillaries from posterior row. Setigers 1–3 with 1–2 (3) straight acicular spines per neuropodium (Fig. 3c). Setiger 4 and following setigers with single vertical row of rostrate hooks (Fig. 3d, e). Number of rostrate hooks varies along body and with body size increasing to a maximum in mid-body setigers and thereafter decreases progressively towards the last setiger. Large specimens with 4–5 hooks in setiger 4, up to 20 hooks in mid-body setigers, and 8–10 hooks in the posterior most setiger. Rostrate hooks of setiger 4 with 2–3 apical teeth above the main fang and few, short subrostral fibrils, or fibrils absent (Fig. 3d). Fully developed hooks from setiger 5, each with four apical teeth above the main fang and several strongly curved subrostral fibrils (Fig. 3e).
Anterior part of body with six internal septa separating setigers 1–7. Three–four pairs of nephridia present, with nephridipores located ventrally beneath row of hooks on setigers 7–11 (Table 1).
Dark-green-to-black pigmentation on head, anterior and posterior setigers and on pygidium. Some specimens with reddish pigmentation on posterior part of setigers 3–7 (Fig. 4a, b).
Flexible, attached, up to about 200 mm long, with inner thin transparent organic layer of fine and regular woven mesh of fibres, incrusted with fine-particulate material (Fig. 4e). The tubes of several specimens are often tightly felted into a thick crust (Fig. 4c, d).
Sexes are separate and several females with oocytes in mid-body setigers and males with sperm were observed (Table 1). Oocytes of variable size, discoid, up to about 240 μm in diameter. Asexual reproduction by architomy was observed. A specimen divides into two fragments at setiger 12/13, each of which subsequently regenerates the lost parts. The two specimens, after undergoing architomic division, were found in the same tube. Several specimens regenerating posterior or anterior end were also observed separately.
The species is named after the Norse god Loki and subsequently the Loki’s Castle vent field.
The new species is referred to the subgenus N. (Loxochona) based on presence of an asymmetric pygidial funnel, with the base of the funnel being oblique with a ventrally placed anal opening, and the absence of nephridial papillae on setiger 6 (Arwidsson 1906). Some confusion about the number of species referred to the subgenus N. (Loxochona) exists in the literature. De Assis et al. (2007a) referred the following six species to the subgenus: N. arwidssoni Blake, 1985; N. quadrispinata Arwidsson, 1906; N. trispinata Arwidsson, 1906
N. canadensis McIntosh, 1913; N. ohtai Miura and Hashimoto, 1991; and N. venticola Blake and Hilbig, 1990. De Assis et al. (2007b) referred, in addition, two more species, N. personata Johnson, 1901 and N. maculata Arwidsson, 1911
, to the subgenus. However, N. canadensis, N. maculata and N. personata are all well-documented members of the subgenus N. (Nicomache) Arwidsson, 1906, as they all possess a more or less symmetrical pygidial funnel with a centrally placed anus within the funnel, and nephridial papillae present on setiger 6 (not known for N. canadensis) (Johnson 1901; Arwidsson 1911; McIntosh 1913; Arwidsson 1922; Imajima and Shiraki 1982). To summarize, the subgenus N. (Loxochona) comprises at present six species, including the new species described herein (Table 2). N. (L.) lokii sp. nov. differs from N. (L.) ohtai, N. (L.) quadrispinata and N. (L.) trispinata in the absence of an asetous preanal segment and the absence of spiral notosetae. Further, it differs from N. (L.) arwidssoni and N. (L.) venticola, both known from hydrothermal vent habitats, in the number of setigerous segments and in maximum number of hooks per setiger. N. (L.) venticola differs from both N. (L.) arwidssoni and N. (L.) lokii sp. nov in the number of acicular spines per neuropodium in setigers 1–3.
A pronounced difference in size and abundance of N. (L.) lokii sp. nov. was observed when comparing samples from the black smoker chimney walls and the low-temperature sedimentary area. On the chimney walls, small specimens (generally smaller than 25 mm) form thin crusts of tubes heavily incrusted by ferrous material (Fig. 4c). In the sedimentary Sclerolinum field, large specimens (up to 125 mm) form an up to 5-cm-thick mat in the upper part of the sediment (Fig. 4d). Just below this mat, the sediment is anoxic, and a minor part of the Sclerolinum tubes penetrate this deep into the sediment. The observed stable isotope values of δ13C = −22.5 and δ15N = 3.8 suggest that N. (L.) lokei sp. nov. is a grazer, utilizing both the bacterial mats found on the chimney walls and on the sediment surface as well as sinking particles from the water column. This is supported by the morphology of the foregut in N. (L.) lokei sp. nov., where the ventral pharynx is well developed and may be used for scraping off food particles from the substrate (Tzetlin and Purschke 2005). However, the sulphur isotope signal (δ34S = 11.1) indicate a trophic relationship with the microbial community (Kennicutt et al. 1992).
SEM micrographs of the inner gut show that the inner wall is densely populated by bacteria (Fig. 4f). From our 16SrDNA clone library of the endobiont community, a total of 53 sequences were obtained. Through DOTUR analysis, we obtained four OTUs with a distance level of 1%. A pronounced dominance of bacteria clustering within the Sphingomonas was found (43 out of 53 sequences), with more than 99% sequence similarity with Sphingomonas melonis Buonaurio et al., 2002
. Further phylogenetic analysis using ARB confirmed these results as all the sequences clustered within the phylum Proteobacteria, where the majority clustered within the alphaproteobacteria and the genus Sphingomonas, a group generally known as decomposers (data not shown).
The mat of polychaete tubes provides both a shelter and substrate for a rich and specialized polychaete assemblage as well as clusters of nematodes and dense populations of gastropods of the genera Pseudosetia and Skenea.