Kainonereis polaris ( Hartman, 1967 ) Conde-Vela & Wu & Salazar-Vallejo, 2018

Conde-Vela, Víctor Manuel, Wu, Xuwen & Salazar-Vallejo, Sergio Ignacio, 2018, Elisesione imajimai Jimi & amp; Eibye-Jacobsen & amp; Salazar-Vallejo 2018, sp. nov., Zoological Studies (Zool. Stud.) 57 (6), pp. 1-24 : 16-20

Kainonereis polaris ( Hartman, 1967) comb. n.

( Figs. 1D ; 2 I-J; 7A-I; 8A-K)

Nicon polaris Hartman 1967:68-69 , Pl. 19, Figs. 19A-E.

Type material: Antarctic Ocean , Antarctica. Holotype USNM 55514 , female epitoke, and paratype USNM 55515 , atoke, R/ V Eltanin, Sta. 432 (62°53'31.2"S, 59°21'W), South Shetland Islands , Nelson Island, Coll. University of Southern California, 884-935 m, 7 January 1963.

Type locality: Bransfield Strait, 884-935 m depth.

Epitoke description: Holotype ( USNM 55514) complete, female epitoke, 22 mm long, 1 mm wide at chaetiger 10, 66 chaetigers. Specimen in good condition, body yellowish, tapering posteriorly, parapodia previously dissected, no staining pattern observed.

Prostomium wider than long, pentagonal, anterior margin entire, medial shallow groove present; one pair of antennae, not articulated; eyes faded, reddish, rounded, subequal, posterior eyes on lappets extended over achaetous ring ( Fig. 7A ). Achaetous ring as long as first chaetiger; anterior cirri with distinct cirrophores, cirrostyles articulated, longest reaching chaetiger 5 ( Fig. 7A ). Pharynx bare; jaws dentate, cutting edge with 5-6 teeth visible, eroded teeth ( Fig. 7C ).

Body divided into two regions: 1) pre-natatory region include chaetigers 1-14, sub-divided into three regions; 2) natatory region from chaetiger 15 to end of body.

First two chaetigers with neuroaciculae only, remaining with both noto- and neuroaciculae. In chaetigers 3-4 ( Fig. 1D ), dorsal cirrus swollen basally, cirrostyle narrow, digitate, distinctly separated from cirrophore. Both notopodial dorsal and ventral ligules digitate, subequal. Acicular neuropodial ligule subconical, half as long as postchaetal lobe; postchaetal lobe digitate; neuropodial ventral ligule digitate, slightly longer than postchaetal lobe. Ventral cirrus pyriform, cirrostyle slightly distinct.

In chaetigers 5-7 ( Fig. 7D ), dorsal discs petal-like, disc with thin, folded margin; cirrostyle narrow, laterally inserted. Notopodial dorsal ligule as long as notopodial ventral one; both ligules subconical, separated by a short, rounded prechaetal lobe. A c i c u l a r n e u r o p o d i a l l i g u l e s u b c o n i c a l, a s long as postchaetal lobe; neuropodial ventral ligule subconical, slightly longer than acicular neuropodial lobe. Ventral cirrus cirriform, half as long as acicular neuropodial lobe.

In chaetigers 8-14 ( Figs. 2I ; 7E ), dorsal cirrus cirriform, as long as notopodial dorsal ligule. Both notopodial dorsal and ventral ligules subequal, subconical, tapering, separated by a short, digitate prechaetal lobe. Acicular neuropodial ligule subconical; postchaetal lobe digitate, half as long as acicular neuropodial ligule; neuropodial ligule subconical, as long as acicular neuropodial lobe. Ventral cirrus cirriform, half as long as acicular neuropodial lobe.

Parapodia from 15 to end of body similarly modified throughout ( Figs. 2J ; 7 F-G). Dorsal cirrus smooth, twice longer than notopodial dorsal ligule, with two small basal, lateral lamellae, upper lamella larger than lower one; dorsal lamella twice longer than upper one, division between it and upper lamella slightly conspicuous. Both notopodial dorsal and ventral ligules digitate, subequal; both notopodial ligules separated by a large, rounded prechaetal lobe. Acicular neuropodial ligule digitate; postchaetal lobe becoming into a lamella, as wide as and longer than acicular neuropodial ligule, tip with a rounded lobe and a small apex; neuropodial ventral ligule digitate, medially inserted to and half as long as acicular neuropodial ligule. Ventral cirrus cirriform, as long as acicular neuropodial ligule, with two large basal lamellae.

Notochaetae homogomph spinigers. Neurochaetae homogomph spinigers and heterogomph falcigers in supra-acicular fascicles; heterogomph spinigers and falcigers in sub-acicular fascicles.

Notopodial homogomph spinigers pectinate, teeth decreasing in size towards tip. Neuropodial heterogomph spinigers pectinate, teeth fine, decreasing towards tip. Neuropodial heterogomph falcigers pectinate, teeth minute, distal tooth stout, incurved, fused to blade ( Figs. 7 H-I); supra- and sub-acicular falcigers similar, both decreasing in size slightly towards posterior chaetigers.

Pygidium with two lobes ( Fig. 7B ); anal cirri as long as last seven chaetigers ( Fig. 7B ).

Atoke description: Paratype ( USNM 55515) incomplete, 16 mm long, 1 mm wide at chaetiger 10, 40 chaetigers. Specimen in good condition, body yellowish, tapering posteriorly, no pigmentation pattern observed. Tube flexible, incorporating fine sediment particles, with algal stipe-like structures and shell fragments attached ( Fig. 8D ).

Prostomium wider than long, pentagonal, anterior margin entire, medial shallow groove present; one pair of antennae, not articulated; eyes faded, subequal, posterior eyes lappets absent ( Figs. 8A, B ). Achaetous ring as long as first chaetiger; anterior cirri with distinct cirrophores, cirrostyles articulated, longest anterior cirri reaching chaetigers 9-10 ( Fig. 8A ). Pharynx bare; jaws dentate, cutting edge with 6-7 visible teeth ( Fig. 8C ).

Parapodial cirri pattern. Dorsal cirri cirriform, longer than notopodial dorsal ligules throughout body; basally inserted on anterior region, displaced medially toward posterior body. Ventral cirri cirriform, basally inserted throughout body, subequal to neuropodial ventral ligules in anterior region, progressively diminishing in size, becoming half as long as ventral ligules towards posterior end.

First two chaetigers with neuroaciculae only, remaining with both noto- and neuroaciculae. In chaetigers 1-2 ( Fig. 8H ), dorsal cirrus cirriform, 1.5 times longer than dorsal ligule. Dorsal ligule as long as postchaetal lobe and neuropodial ventral ligule; acicular neuropodial ligule subconical, half as long as postchaetal lobe.

Ventral cirrus cirriform, as long as neuropodial ventral ligule.

In chaetigers 3-4 ( Fig. 8I ), notopodial dorsal ligule present, as long as notopodial ventral one; remaining structures as in first two chaetigers.

In anterior and middle chaetigers ( Fig. 8J ), dorsal cirrus cirriform, slender, 1.2 times longer than notopodial dorsal ligules. Both notopodial dorsal and ventral ligules subequal, conical, tapering, twice longer than prechaetal lobe; prechaetal lobe digitate. Acicular neuropodial ligule subconical, twice longer than postchaetal lobe; postchaetal lobe digitate; neuropodial ventral ligule subconical, tapering, as long as acicular neuropodial ligule. Ventral cirrus cirriform, half as long as neuropodial ventral ligule.

In posterior chaetigers ( Fig. 8K ), dorsal cirrus more displaced medially; remaining structures as in anterior and middle chaetigers.

Notochaetae homogomph spinigers. Neurochaetae homogomph spinigers and heterogomph falcigers in supra-acicular fascicles; heterogomph spinigers and falcigers in sub-acicular fascicles.

Notopodial homogomph spinigers pectinate, teeth decreasing in size towards tip ( Fig. 8E ). Neuropodial heterogomph spinigers pectinate, teeth fine, decreasing towards tip, shorter than notopodial ones ( Fig. 8G ). Neuropodial heterogomph falcigers pectinate, teeth minute, distal tooth stout, incurved, fused to blade ( Fig. 8F ); supra- and sub-acicular falcigers similar, both decreasing in size slightly towards posterior chaetigers.

Pygidium missing.

Remarks: Kainonereis polaris comb. n. is easily recognized by having dorsal cirri twice longer than notopodial dorsal ligules and large postchaetal lamellae with a distal apex in natatory parapodia; whilst remaining species have dorsal cirri subequal and postchaetal lamellae with one or two rounded, distal lobes. This species has a remarkable prostomial modification, which was called ‘lappets’ by Hartman, clearly illustrated in the original drawing ( Hartman 1967, Fig. 19A). The lappets consist of a hypertrophy of the posterior prostomial margin and carry the posterior eyes ( Fig. 7A ). Like the hypertrophied antennal bases in K. alata , these features are regarded as exclusively present in K. polaris comb. n. Further, although their presence was not used as a diagnostic feature for this species, they cannot be regarded as a preservation artifact. Furthermore, the petal-like discs resemble those found in K. alata , but in K. polaris comb. n. they are large, covering the complete dorsal surface of the corresponding chaetiger, whilst in K. alata they are short, not covering the chaetigers.

Hartman (1967:68) included two specimens in her description, one was indicated as the type and as an epitoke, but for the atoke she wrote ( Hartman 1967:69): “Its atokous stage has not been identified.” The comparison of prostomial shape, antennae, eyes, jaws, anterior cirri, the absence of pharyngeal ornamentation, the almost identical shape of parapodial processes and chaetae along chaetigers 8-14, ensure the conspecificity of atoke specimen with the epitoke one. This is the only Kainonereis species of which the atokous stage is known. A remarkable feature is the appearing of notopodial dorsal ligule from chaetiger 3 as in epitokal females of other species. Also, the vial with the atoke also contains a tube, as wide as the worm, such that if it belonged to the atoke, at least this species has tubiculous habits. In all Kainonereis species, blades of neuropodial falcigers are subequal, finishing in an incurved, fused tooth, giving them a hooked appearance, as usual in other tubiculous genera such as Platynereis (e.g. Daly 1973; Read 2007; Cañete et al. 2013; Darbyshire 2014, Merz 2015).

This species was originally regarded as belonging to Nicon ; however, Hartman recognized the high dissimilarity among conspecifics ( Hartman 1967:68). The features she recognized as relevant were the diverging antennae, dentition of jaws, and the prostomial posterior prolongations (lappets) carrying the posterior eyes ( Hartman 1967:69), but not the elytriform cirri in chaetigers 5-7. The only Nicon species known with fully developed heteronereis is N. aestuarensis Knox, 1951 , but it differs from epitokes of Kainonereis by having smooth anterior cirri, only one large lamella above dorsal cirri, notopodial ventral ligules develop a lamella, and lack large, rounded prechaetal lobes separating considerably the notopodial ligules ( Knox 1951).

Atoke specimens could be easily confused with other Nicon species, especially because the contemporary (e.g. Hartman 1958) and current ( de León-González and Trovant 2013) generic diagnosis overlap features such as the bare pharynx, notopodial prechaetal lobes and only homogomph spinigers in notopodia. Based on the presence of notopodial prechaetal lobes, N. polaris was regarded as resembling N. aestuarensis , N. japonicus Imajima, 1972 , N. rotunda Hutchings and Reid, 1990 , and N. sinica Wu and Sun, 1979 ( de León-González and Trovant 2013:70). Although, these species differ notably from K. polaris comb. n.: N. japonicus lacks articulated anterior cirri, and its neuropodial falcigers are anchylosed; N. rotunda has neuropodial homogomph falcigers in anterior chaetigers, and lacks heteronereis phase; and N. sinica has distally, faintly annulated (not articulated) anterior cirri ( Imajima 1972, Wu and Sun 1979, Hutchings and Reid 1990). Finally, in the short redescription of Nicon pictus Kinberg, 1865 (type species of Nicon ), Hartman (1948) included the presence of neuropodial homogomph falcigers, and large postchaetal lobe in posterior chaetigers; these features are absent in the atoke of K. polaris comb. n. It may be noted that Kainonereis is a better-defined set of species in comparison to Nicon that currently includes different body patterns with distinct features ( De León-González and Trovant 2013).

The atoke of K. polaris comb. n. also differs from R. zebra , the type species of Rullierinereis Pettibone, 1971 , in both having notopodial dorsal ligules and lacking notopodial homogomph falcigers in posterior chaetigers. In Rullierinereis , R. mexicana was described based on male and female specimens, being the only species with known epitokes. It can be easily separated from Kainonereis species because it has three body regions instead of two, and males lacks notopodial homogomph falcigers and elytriform structures in chaetigers 5-7 ( Treadwell 1942, Hartman 1956, Pettibone 1971).

Figures

Fig. 1. Morphology of Kainonereis Chamberlin, 1919 species. K. chamberlini sp. n. A-C, E (USNM 1422199); K. polaris comb. n. D (USNM 55514). (A) anterior end, dorsal view (transparency, 10x); (B) elytriform dorsal cirrus from mounted parapodium 6, anterior view; (C) same, non-mounted, lateral view; (D) parapodium 3, anterior view; (E) parapodium 40, anterior view. Abbreviations: Ac, anterior cirri; An, antennae; Cr, cirrostyle; DoLa, dorsal lamella of dorsal cirri; Di, disc; Jw, jaws; LDc, lower lamella of dorsal cirrus; LVc, lower lamella of ventral cirrus; NaL, neuroacicular ligule; NeV, neuropodial ventral ligule; NoD, notopodial dorsal ligule; NoV, notopodial ventral ligule; Ph, pharynx; PoL, neuropodial postchaetal lobe; Pr, prostomium; PreL, notopodial prechaetal lobe; St, stalk; UDc, upper lamella of dorsal cirrus; UVc, upper lamella of ventral cirrus; Vc, ventral cirrus; VeLa, ventral neuropodial lamella. Scale bars: A = 0.3 mm; B-E = 50 µm. All chaetae omitted.

Fig. 2. Drawings from parapodia of Kainonereis species. K. alata A, B (USNM 19386); K. chamberlini sp. n. C (UMML 22.1126), D (USNM 1422199); K. elytrocirra comb. n. E, F (MBMCAS A-44); K. peltifera sp. n. G, H (LACM-AHF 7400p); K. polaris comb. n. I, J (USNM 55514). (A) parapodium 11, anterior view; (B) parapodium 40, anterior view; (C) parapodium 11, anterior view; (D) parapodium 25, anterior view; (E) parapodium 12, anterior view; (F) parapodium 20, anterior view; (G) parapodium10, anterior view; (H) parapodium 22, anterior view; (I) parapodium 13, posterior view; (J) parapodium 30, posterior view. Scale bars: A, B = 50 µm; C-H = 0.1 mm; I-J = 0.2 mm. E redrawn from Wu and Sun (1979:109). All chaetae omitted.

Fig. 7. Kainonereis polaris (Hartman, 1967) comb. n. Holotype female (USNM 55514). (A) anterior end, dorsal view (arrows point lappets); (B) posterior end, dorsal view; (C) anterior end, pharynx, ventral view; (D) parapodium 7, anterior view; (E) parapodium 13, anterior view; (F) parapodium 19, anterior view; (G) parapodium 30, anterior view; (H) neuropodial supra-acicular heterogomph falciger, parapodium 13; (I) neuropodial sub-acicular heterogomph falciger, parapodium 13. Scale bars: A = 1 mm; B, C = 0.5 mm; D-G = 0.2 mm; H, I = 10 µm.

Fig. 8. Kainonereis polaris (Hartman, 1967) comb. n. Paratype atoke (USNM 55515). (A) anterior end, dorsal view; (B) close-up of prostomium; (C) anterior end, pharynx, ventral view; (D) tube; (E) notopodial homogomph spiniger, parapodium 13 (insert: closeup of teeth); (F) neuropodial sub-acicular heterogomph falciger, parapodium 13; (G) neuropodial sub-acicular heterogomph spiniger, parapodium 1; (H) parapodium 1, anterior view; (I) parapodium 3, anterior view; J parapodium 13, anterior view; K parapodium 37, anterior view. Scale bars: A-D = 0.5 mm; E = 20 µm; F, G = 10 µm; H-K = 0.2 mm.