Kainonereis Chamberlin, 1919

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 : 3-5

Genus Kainonereis Chamberlin, 1919

Kainonereis Chamberlin 1919:194 (key), 196 (etymol.).

Type species: Kainonereis alata Chamberlin, 1919 , by original designation.

Diagnosis: (emended, new features highlighted in boldface). Two antennae, separate (not fused) or sometimes basally fused in male epitokes, articulated in some species. Four pairs of articulated anterior cirri. Pharynx bare. Chaetigers 1 and 2 with neuroacicula only. Notopodial prechaetal lobes present, subconical to digitate in atokes, rounded in epitokes. Body of epitokes divided into two regions (one pre-natatory and one natatory). Chaetigers 5-7 with dorsal cirri modified into elytriform structures or dorsal discs in epitokes. Males with notopodial homogomph falcigers and spinigers in chaetigers 1-7. Females with notopodial homogomph spinigers in chaetigers 1-7. Notopodial dorsal ligule present from chaetiger 4 in males, chaetiger 3 in females.

Distribution: Species of the genus are found in tropical, temperate and polar regions, from surface down to 935 m depth; habitat unknown.

Remarks: Species belonging to Kainonereis are easily identified by having elytriform dorsal cirri in chaetigers 5-7 only in epitokes. Chamberlin (1919) noted that their specimens were similar to other already described heteronereis; however, he considered two main attributes as sufficient to erect a new genus: the bifurcate appendages on the prostomium, and the elytriform structures on chaetigers 5-7. Even in the key, Chamberlin (1919:194) used the basally fused antennae as the main feature to separate it from all other genera. Also, he thought that Kainonereis was closely related to Nereis ( Chamberlin 1919:197) , perhaps after the epitokal condition of the specimens, and because he did not observe the everted pharynx.

K. alata has only been recorded once since its original description from the Eastern Tropical Pacific ( Hernández-Alcántara and Solís-Weiss 1991:254). Two additional records of Kainonereis species have been made but in other genera: one from the Yellow Sea as a new species of

Rullierinereis Pettibone, 1971 , R. elytrocirra by Wu and Sun (1979); and another from Antarctica as a new species of Nicon Kinberg, 1865 , N. polaris by Hartman (1967).

It must be emphasized that atoke morphology of Kainonereis was unknown until now. An atoke specimen was found as part of N. polaris ’ type material, but it was not described even though it was available at the time of its first description ( Hartman 1967:68). This specimen has bare pharynx, articulated anterior cirri, notopodial prechaetal lobes and only homogomph spinigers in notopodia, all these are diagnostic features of Nicon ( de León-González and Trovant 2013:69) . However, although roughly similar, there are sufficient features to separate Kainonereis atokes from Nicon ones (see below, under K. polaris ( Hartman, 1967) comb. n.).

Subfamily placement: The subfamily affinities of Kainonereis have not been addressed previously. Even though Kainonereis was well described and illustrated, it was not included in previous phylogenetic analyses ( Fitzhugh 1987; Santos et al. 2005), likely because the incompatibility of adding epitoke features are not compatible with an atoke-based matrix, avoiding unnecessary problems.

Based on the supposed relationship with Nicon and Rullierinereis , Kainonereis could be placed in Gymnonereidinae sensu Fitzhugh (1987) , or in any subfamily in the Santos et al. (2005) phylogeny; it did not show close affinity with related genera Nicon and Rullierinereis , or with any other remaining genera, and therefore they could not be placed in a specific subfamily ( Santos et al. 2005). Given that Kainonereis is not compliant with any subfamily as currently defined, it is regarded here as subfamily incertae sedis. This situation must not affect its recognition as a valid genus, since it can be separated from other genera without paragnaths or papillae.

Epitokal morphology

Kainonereis species share some distinctive epitokal features that diverge from typical nereidid morphology. To help recognize them, relevant features of the genus are summarized and illustrated in figure 1.

Parapodia

Based on the transformation of parapodia, epitokes have two body regions: a non-natatory region comprising chaetiger 1 to 14, and a natatory region comprising chaetigers 15 to the end of the body. In turn, the non-natatory region is sub-divided into three regions, based on the modifications in parapodial cirri: a) chaetigers 1-4 with both dorsal and ventral cirri basally to medially swollen; b) chaetigers 5-7 with dorsal cirri elytriform and ventral cirri cirriform; c) chaetigers 8-14 with both dorsal and ventral cirri cirriform. Other relevant features are: the late appearing of notopodial dorsal ligule up to chaetiger 4 in males ( Fig. 6E ), while in females it appears from chaetiger 3 ( Fig. 1D ); the notopodial prechaetal lobes increase in size and become rounded, separating notably the dorsal and ventral notopodial ligules ( Figs. 1 D- E); and the absence of crenulated dorsal cirri in parapodia from natatory region of males.

The parapodia of the natatory region have a set of lamellae. Dorsal and ventral cirri develop two basal lamellae, one above or upper, and one below or lower of each cirrus ( Fig. 1E ); generally, the upper lamella is larger than the lower one in both cirri. Also, a larger, dorsal lamella is present, not always well defined and separated from the upper lamella of dorsal cirri ( Fig. 1E ). Moreover, neuropodial postchaetal lobes become modified into a large lamella, typically distally multilobate ( Fig. 1E ).

Dorsal discs

Chaetigers 5-7 are distinct by having modified elytriform structures ( Figs. 1 A-C). There were some doubts concerning how dorsal cirri are modified into elytra-like features, or if they are separate structures. In K. elytrocirra comb. n. ( Wu and Sun 1979, Fig. 8d ) and in K. polaris comb. n. ( Hartman 1967, Pl. 19, Fig. B), the cirrostyle was illustrated as arising from the stalk, whereas in K. alata , it was illustrated as inserted to the elytriform structure ( Chamberlin 1919, Pl. 28, Fig. 9). The examination of the type material of K. elytrocirra comb. n. and K. polaris comb. n. confirms that cirrostyles are not basal nor projected from the stalk, but rather arise from the elytriform structure.

Although there is no clear discontinuity, stalk and disc are distinguished in the cirrophores of Kainonereis : the stalk is the narrow, basal section, while the disc is the plate-like, distal one; it must be added that the disc surface has no ornamentation ( Figs. 1 A-C). The stalk is inserted in the lower disc surface, i.e., a peltate insertion, as it is clear in K. peltifera sp. n. ( Fig. 6B ), but not so obvious in the other species. This is because their discs are not rounded, and are arranged vertically in relation to the parapodium. The discs can be modified into thick structures, as in some specimens of K. alata and K. chamberlini sp. n. ( Figs. 3F and 4E , respectively), likely resulting from the fixation process. Finally, the cirrostyles are the short, distal portion, generally attached to the lower surface of the discs ( Figs. 1 A-C), not always completely discernible.

Chaetae

Chaetae only include notopodial homogomph falcigers along chaetigers 3-7 in male epitokes. At first instance, the presence of notopodial homogomph falcigers in K. alata was regarded as a specific trait ( Chamberlin 1919). However, females of K. chamberlini sp. n., K. peltifera sp. n. and K. polaris comb. n. do not have notopodial homogomph falcigers, only notopodial spinigers along chaetigers 3-14. This fact indicated sex-related chaetal dimorphism in Kainonereis species. It is well known that epitoke males and females are dimorphic in parapodial morphology, but chaetal dimorphism is really rare in nereidids; one example is the presence of simple, ribbed chaetae in posterior chaetigers of males of Platynereis p u l c h e l l a G r a v i e r, 1 8 9 9 a n d P. p o l y s c a l m a Chamberlin, 1919 ( Gravier 1899; Chamberlin 1919; Holly 1935).

Sex

Males were identified by the presence of whitish sperm bundles in coelom of K. peltifera sp. n., or free sperm in K. alata and K. elytrocirra comb. n. Certainly, the morphology of sperm could not be observed directly under a compound microscope, but the whitish color, shape and position in body and parapodia of both bundles and free-floating tiny spheres are indicative of male gametes. A female specimen of K. peltifera sp. n. was the only one with few oocytes in coelom and parapodia. Epitoke specimens of K. chamberlini sp. n. and K. polaris comb. n. were identified as females after comparison with K. peltifera sp. n.

Figures

Fig. 6. Kainonereis peltifera sp. n. A, B, holotype male (POLY-AHF 7400h); E, J-L, paratype male (POLY-AHF 7400p); C, D, F-I, M, N, paratype females (POLY-AHF 7400p). (A) anterior end, dorsal view; (B) close-up of chaetigers 5-7, dorsal view; (C) close-up of anterior end, dorsal view; (D) parapodium 1, anterior view; (E) parapodium 3, anterior view; (F) parapodium 6, anterior view; (G) parapodium 10, anterior view; (H) parapodium 22, anterior view; (I) parapodium 45, anterior view; (J) notopodial homogomph falciger, parapodium 3; (K) neuropodial sub-acicular falciger, parapodium 3; (L) neuropodial sub-acicular spiniger, parapodium 3; (M) neuropodial supra-acicular falciger, parapodium 10; (N) neuropodial sub-acicular falciger, parapodium 10. Scale bars: A, B, = 0.5 mm; C-I = 0.1 mm; J-N = 10 µm.

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. 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.

Fig. 3. Kainonereis alata Chamberlin, 1919. Paratypes males (USNM 19386). (A) whole specimen, dorsal view; (B) anterior end, dorsal view; (C) anterior end, ventral view; (D) close-up of prostomium, dorsal view (arrow points beginning of ceratostyles); (E parapodium 3, anterior view; (F parapodium 5, anterior view; (G) parapodium 11, posterior view; (H) close-up of noto- and neuropodium, chaetiger 3 (dorsal and ventral cirri omitted); (I parapodium 40, posterior view; (J) notopodial homogomph falciger, parapodium 2; (K) pygidium, dorsal view. Abbreviations: An, antennae; Pa, palps. Scale bars: A = 1 mm; B, C = 0.5 mm; D, K = 0.1 mm; E-I = 50 µm; J = 10 µm.

Fig. 4. Kainonereis chamberlini sp. n., A-C, F-H, J, K, holotype (USNM 1422199); D, E, I, paratype (UMML 22.1126). (A) whole specimen, dorsal view; (B) anterior end, dorsal view; (C) same, lateral view; (D) whole specimen, dorsal view; (E) same, lateral view; (F) neuropodial sub-acicular heterogomph spiniger, chaetiger 6; (G) neuropodial sub-acicular heterogomph falciger, parapodium 6; (H) parapodium 6, anterior view; (I) parapodium 11, anterior view; (J) parapodium 25, anterior view; (K) parapodium 40, anterior view. Scale bars: A, D = 1 mm; B, C, E = 0.5 mm; F, G = 10 µm; H-K = 0.1 mm.