Travisia sanrikuensis, Kobayashi & Kojima, 2021

Kobayashi, Genki & Kojima, Shigeaki, 2021, Travisia sanrikuensis, a New Species of Travisiidae (Annelida) from the Lower Bathyal Zone of the Northwestern Pacific, Species Diversity 26 (2), pp. 131-136 : 134-135

Travisia sanrikuensis sp. nov.

( Figs 2 , 3 )

Type material. Holotype: (NSMT-Pol H-827), off Miyagi, Japan, the northwestern Pacific , the cruise KS-16-18 ( R / V Shinsei-Maru), St. ON 6, 11 November 2016, 871– 880m deep, 38°23′57″–22′58″N, 142°20′05″E, collected using a 3 m beam trawl. Four paratypes: (NSMT-Pol P-828–P-831), from the same sample as the holotype.

Other material examined. Non-type specimen: off Otsuchi, Japan, the northwestern Pacific, the cruise KS-17- 12 ( R / V Shinsei-Maru), St . Bent4, 3 October 2017, 1659– 1684 m deep, 39°17′30″–18′18″N, 142°48′25″–49′59″E, collected using a 3 m beam trawl, identifier GK627, 1 specimen.

Description. All type specimens complete. 18.9–25.8 mm (holotype 24.6 mm) in length and 5.0–6.4 (holotype 5.8 mm) in width at widest segment, whitish in alcohol, without pigmentation ( Fig. 2A–C ). Epidermal papillae present, indistinctive without Methyl green staining ( Fig. 3 ). All specimens with 25 segments; first 20 segments chaetigerous, last five achaetous. Achaetous segments less developed ( Fig. 2E ) except first achaetous segment in the posterior region of paratype (NSMT-Pol P-829). Prostomium conical, eyes absent, a pair of nuchal organs present as dorsolateral slits. Peristomium short restricted to the mouth; mouth ventral with folds ( Fig. 2D ). Parapodia biramous, no parapodial lamellae on chaetiger 1. Parapodial lappets developed from chaetiger 15 or 16 to end of body. Subsequent parapodia very small. All chaetae capillary, approximately 10–20 per ramus, most chaetae shorter than branchiae. Notopodial and neuropodial chaetal rami well separated. Transverse ridges projected on last 10–11 segments, but somewhat indistinct in relaxed specimens. Middle body triannulate, an- teriorly and posteriorly less annulated (biannulate or not annulated). Annulation in lateral body indistinctive. Branchiae cirriform from chaetiger 2 (19 pairs) except for paratype (NSMT-Pol P-829) with 20 branchiae, the last one short. Branchiae just posterior to notochaetae, long on middle chaetigers, short on first 3–4 chaetigers and most posterior chaetigers. Interramal pores, present on all chaetigers, posterior ones indistinct ( Fig. 2F ). Mid-ventral groove absent. Pygidium with shallow incisions, resulting in about 8 lobes around terminal anus ( Fig. 2E ). Methyl green staining pattern not characteristic in entire body, except white band (non-staining) on prostomium ( Fig. 3 )

Type locality. Off Miyagi, the Sanriku region, Japan, 871– 880 m deep .

Etymology. The specific epithet sanrikuensis refers to the Sanriku region, encompassing the three prefectures Aomori, Iwate, and Miyagi, in the northeastern part of Japan, from where the specimens were collected, with the Latin suffixensis.

Remarks. Travisia sanrikuensis sp. nov. morphologically resembles Travisia chiloensis Kükenthal, 1887 and Travisia oksae Hartmann-Schröder and Parker, 1995 , based on the taxonomic key presented by Rizzo and Salazar-Vallejo (2020). However, there are certain differences between T. sanrikuensis sp. nov. and these two species with respect to the number of segments, chaetigers, branchiae, and achaetous segments [note that achaetous segments in the posterior region of Travisia are regarded as annulations of the pygidium by Maciolek and Blake (2006)] ( Table 3): 25 segments in T. sanrikuensis sp. nov. versus 27 in T. chiloensis ; 20 chaetigers in T. sanrikuensis sp. nov. but 24 in T. chiloensis ; 5 posterior achaetous segments in T. sanrikuensis sp. nov. although 3 or less in T. oksae ; and 19 or 20 pairs of branchiae in T. sanrikuensis sp. nov. compared with 22 pairs in T. oksae . In addition, these three species show notable differences in bathymetric and/or geographic distribution: T. sanrikuensis sp. nov. inhabits sea beds in Japanese waters at depths from 871 to 1684m, whereas T. chiloensis is described from Chile [water depth unavailable from Kükenthal (1887)] and T. oksae is described from South Australia at depths of up to 18 m ( Kükenthal 1887; Hartmann- Schröder and Parker 1995).

The results of phylogenetic analysis based on mitochondrial 16S rRNA gene sequences indicate that T. sanrikuensis sp. nov. is clustered with Travisia brevis (posterior probability=1.0, ML bootstrap value=100%) ( Fig. 4 ) collected from the eastern Pacific (Friday Harbor, WA) ( Paul et al. 2010). However, the genetic difference between these two species is quite large (3.4–3.7%, 11–12 bp of 321 bp) compared with the variation among three specimens of T. sanrikuensis sp. nov. (<0.6%, ≤2 bp in 321 bp). T. sanrikuensis sp. nov. and T. brevis also differ in the following morphological characters ( Table 3): the number of segments (25 in T. sanrikuensis sp. nov. vs. 29 in T. brevis ) and branchiae (19 or 20 in T. sanrikuensis sp. nov. vs. 22 in T. brevis ); branchiae starting from chaetiger 2 in T. sanrikuensis sp. nov. but from chaetiger 3 in T. brevis ( Moore 1923; Rizzo and Salazar-Vallejo 2020). The numbers of branchiae and chaetigers have been established as key diagnostic characters for distinguishing travisiid species ( Rizzo and Salazar-Vallejo 2020). Moreover, T. sanrikuensis sp. nov. and T. brevis differ with respect to bathymetric distribution, with T. sanrikuensis sp. nov. being collected from the lower bathyal zone (871–1684 m depths), whereas T. brevis was collected from the sublittoral zone (50–110 fathoms, i.e., 91–201 m depths in the eastern Pacific off San Diego, California) in the original description ( Moore 1923). These results indicate that T. sanrikuensis sp. nov. differs sufficiently from T. brevis to be considered new to science.

The new species is distinguishable from all known travisiid species recorded from Japan by following characters: the smaller number of segments (25 in T. sanrikuensis sp. nov.) than T. brevis (29) ( Moore 1923), T. japonica (39–40) ( Fujiwara 1933), and in T. pupa (31–34) ( Moore 1906; Imajima 2009); the numbers of chaetigers (20 in T. sanrikuensis sp. nov.) instead T. forbesii (23–26) ( Dauvin and Bellan 1994), T. forbesii intermedia (26–29) ( Annenkova 1937), T. fusus (28) ( Chamberlin 1919), T. profundi (26) ( Dauvin and Bellan 1994; Rizzo and Salazar-Vallejo 2020), and T. pupa (29) ( Imajima 2009); and the number of branchiae (19–20 in T. sanrikuensis sp. nov.) from T. brevis (22) ( Moore 1923), T. fusus (0) ( Chamberlin 1919), T. glandulosa (0) ( Dauvin and Bellan 1994), T. japonica (26) ( Fujiwara 1933), and T. profundi (12) ( Chamberlin 1919).

Distribution. Japan, the northwestern Pacific, in 871– 1684 m deep.

Figures

Fig. 2. Travisia sanrikuensis sp. nov. holotype (NSMT-Pol H-827). A, Dorsal view; B, ventral view; C, left lateral view; D, anterior end, ventral view; E, posterior end, ventral view; F, close-up view showing details of the lateral morphology. Arrows indicate interramal pores. Scale bars: 10mm (A–C); 1mm (D–F).

Fig. 3. Methyl green staining pattern on the prostomium of a Travisia sanrikuensis sp. nov. paratype (NSMT-Pol P-831), ventral view. Scale bar: 1mm.

Fig. 4. Bayesian phylogeny of travisiid species based on 16S rRNA gene sequences (482 characters). Numbers above branches indicate posterior probability followed by percentage maximum likelihood bootstrap values greater than 50%. Travisia sanrikuensis sp. nov. is shown in bold type.