Antrokoreana asuwaensis Kato & Umemura & Nakano 2022, sp. nov.

Antrokoreana asuwaensis sp. nov.

Figs 1A, B, 2–5

urn:lsid:zoobank.org:act: CA391B59-C457-471B-8DEF-6BBF52DECC1E

Antrokoreana sp. — Umemura et al. (2019: 70).

Material examined. Holotype: KUZ Z4004, ♂, Nanatsuoguchi Mine (entrance: 36.056006°N, 136.197563°E; Fig. 1C), Mt. Asuwa, Fukui City, Fukui Prefecture, Honshu, Japan, 2019-11-23 /12-11, leg. S. Umemura.

Paratypes: 31 specimens collected from the same locality. FCMNH-Ar131, 1 ♀, 2017-12-02, leg. S. Umemura; FCMNH-Ar132, 2 ♂♂, 2018-02-02 /03-02, leg. S. Umemura; FCMNH-Ar206, 2 ♂♂, 2018-03-28 /04-05, leg. S. Umemura; FCMNH-Ar207, 1 ♂, 2018-02-02 /02-26, leg. S. Umemura; FCMNH-Ar208, 2 ♂♂, 2017-12-14 /12-22, leg. S. Umemura; FCMNH-Ar212, 2 ♀♀, 2019-02-27 /03-22, leg. S. Umemura; FCMNH-Ar213, 2 ♂♂, 1 ♀, 2018- 11-28 /12-13, leg. S. Umemura; FCMNH-Ar228, 3 ♂♂, 2 ♀♀, same data as for preceding; FCMNH-Ar232, 2 ♂♂, 2018-11-09 /11-28, leg. S. Umemura; FCMNH-Ar240, 1 ♂, 2019-11-23, leg. S. Umemura; FCMNH-Ar243, 2 ♂♂, 3 ♀♀, same data as for holotype; FCMNH-Ar245, 1 ♀, 2018-11-28 /12-13, leg. S. Umemura; FCMNH-Ar246, 1 ♂, 2019-12-11 /12-24, leg. S. Umemura; FCMNH-Ar250, 1 ♀, same data as for holotype; FCMNH-Ar251, 1 ♂, same data as for holotype; FCMNH-Ar252, 1 ♀, same data as for holotype.

Diagnosis. The new species is clearly distinguishable from all congeners by each coxal process of the anterior gonopods being expanded distally in lateral view, its distal part concave, and its posterior part curved and directed mesad in posterior view.

Description.

Size and number of body rings. Holotype male: 22.3 mm long, vertical diameter of largest body ring 1.0 mm; body with 33 podous rings + 1 apodous rings + telson. Paratype males: 21.5–29.2 mm long, vertical diameter of largest body ring 1.2–1.8 mm; body with 32–36 podous rings + 1 apodous rings + telson. Paratype females: 22.7–27.6 mm long, vertical diameter of largest body ring 1.2–1.9 mm; body with 31–33 podous rings + 1 apodous rings + telson.

Head (Fig. 2). Without ommatidia (Figs 1A, B, 2A); with 4 frontal setae. Labrum (Fig. 2B) with 3 labral teeth, 4 supralabral setae and 15 labral setae (holotype). Mandibular cardo with 1 seta; mandibular stipes with 2 setae, unexpanded in males. Gnathal lobe (Fig. 2C–E): external tooth with 3 cusps; internal tooth with 5 cusps (Fig. 2C); 6 (4 complete + 2 incomplete) pectinate lamellae (Fig. 2D), posterior teeth of each lamella with 2 or 3 finger-like branches (Fig. 2E). Gnathochilarium (Fig. 2F) with triangular promentum. Lamellae linguales each with 4 setae in row, stipites each with 3 distolateral setae, without short medial setae. Antennae (Fig. 2G–I) in holotype, 2.8 mm long, ~2.8× longer than vertical diameter of largest body ring, with 4 apical cones. Lengths of antennomeres I–VIII (VIII = apical cones) (in mm): 0.16 (I), 0.48 (II), 0.55 (III), 0.42 (IV), 0.41 (V), 0.39 (VI), 0.38 (VII) and 0.02 (VIII). Length/width ratio of antennomeres I–VII: 1.2 (I), 3.1 (II), 4.3 (III), 3.4 (IV), 2.7 (V), 2.4 (VI) and 2.7 (VII). Antennomeres V–VI (Fig. 2H) each with terminal corolla of large sensilla basiconica bacilliformia; antennomere VII (Fig. 2I) whole surface covered with numerous short sensilla chaetica among longer sensilla trichodea.

Collum. With whorl of 8 setae located about one-third of collum length from posterior margin.

Body rings (Fig. 3A). Prozona to metazona of each ring with 4–8 transverse furrows on ventral half of lateral surfaces. Metazona dorsal surface smooth, ventral surface with 4–8 longitudinal striae; with posterior marginal whorl of setae, length of mid-body setae ~1.2% of vertical diameter of rings; one pair of ozopores present at center of lateral surface of each metazona of 6th ring to ultimate podous ring. (Fig. 1A, B). Sternum of each ring, free from pleurotergum, with wing-like expansions anteriorly.

Legs (Fig. 3B–D). In holotype, mid-body legs ~1.7× longer than vertical diameter of ring; prefemur to claw in length ratio of 1.0:1.2:1.2:1.0:1.4:0.3 (leg-pair 10). Claw slender, ~7.0× longer than height (holotype); with accessory claw. In males, tibia of leg-pair 1 with 1 long spine directed proximad (Fig. 3B). Femur, post-femur, and tibia of following legs each with adhesive pad (Fig. 3C). Penes (Fig. 3D) shorter than coxae of leg-pair 2, each with 1–3 microsetae apically.

Telson (Fig. 3E, F). Preanal ring without projection, with marginal whorl of setae and 5 additional dorsal setae in front of marginal whorl. Anal valves rounded, each with 7 setae; subanal scale without any modifications, with 2 setae.

Gonopods (Figs 4, 5A–F). Both anterior and posterior gonopods projecting ventrad. Anterior gonopods (Figs 4, 5A–D): each coxal process (cp) expanded distally, distal part concave (Fig. 5C), anterior part with 6 setae on lateral surface (Fig. 4A), posterior part with several setae, curved and directed mesad (Fig. 4B); telopodite (tl) slender, club-shaped, composed of single article, with several long setae on distal margin, field of spine-like setae absent; each flagellum (fl) with minute spinules (sps) distally (Fig. 5D). Posterior gonopods (Fig. 5E, F) slender, straight, with 1 longitudinal furrow, field of spine-like setae absent; anterior surface covered with minute scalelike processes (slps); posterior surface smooth, with 3 or 4 long bristles (lbs) on distal part reaching apex of each posterior gonopod; apex forming 3 flattened branches.

Vulvae (Fig. 5G–I). Each vulva pyriform, located inside body ring 3. Operculum (op) slightly longer than bursa (bu), anterior surface of distal part with 4 setae located in 2 longitudinal rows (Fig. 5G, H). Each valve with pair of setae. Receptaculum seminis (rs) single, long, claviform (Fig. 5I).

Coloration. In life, yellowish brown with the defense glands visible by transparency as reddish spots (Fig. 1B). In ethanol, yellowish white or reddish brown.

Distribution and natural history. Known only from the type locality in Japan. Observed at the Nanatsuoguchi Mine (Fig. 1C) from late autumn (November) to early spring (March) (see Umemura et al. 2019).

Derivatio nominis. The specific name is derived from the type locality of this species.

DNA sequences. Five sequences were obtained: two of a male (FCMNH-Ar251)—28S (INSD accession number, LC654434; 517 bp) and 16S (LC654436; 425 bp); and three of a female (FCMNH-Ar252)—28S (LC654435; 517 bp), COI (LC654438; 658 bp), and 16S (LC654437; 425 bp).

Remarks. The new species is clearly judged to be a member of the genus Antrokoreana as it possesses the following diagnostic characteristics of the genus (Enghoff 1985; Shinohara et al. 2015): 1) head without ommatidia; 2) antennomere VII almost as long as antennomere VI, and its whole surface covered with short sensilla chaetica among longer sensilla trichodea; 3) posterior margin of each ring with one row of setae; 4) tibia of leg-pair 1 with 1 long spine; 5) femur, post-femur, and tibia of other leg pairs with adhesive pads; 6) coxa of leg-pair 2 with pair of penes; 7) both gonopods without fields of spine-like setae; and 8) anterior gonopods with telopodites.

Antrokoreana asuwaensis sp. nov. is distinguishable from all seven congeners, including A. gujoensis and A. uenoi which are endemic to central Honshu, by the distally expanded coxal processes of the anterior gonopods, in accordance with the descriptions of the six species known thus far (Takashima & Haga 1956; Shinohara 1960, 1973; Murakami & Paik 1968; Murakami 1969; Masuda 2010). In common with A. gujoensis and A. takakuwai, the posterior gonopods of A. asuwaensis sp. nov. each bears 3 or 4 long bristles reaching the distal edge of the gonopod (Shinohara 1960, 1973; Masuda 2010); this shared feature suggests these species may be closely related. Future studies are needed to elucidate phylogenetic relationships among Antrokoreana species, and clarify whether A. asuwaensis sp. nov., A. gujoensis and A. takakuwai form a monophyletic lineage.

Molecular analyses. The topology of the BI tree (Fig. 6), which was constructed to estimate the phylogenetic position of Antrokoreana asuwaensis sp. nov., was identical to that of the ML tree (not shown). The monophyly of A. asuwaensis sp. nov. and A. gracilipes was fully supported (BS = 96%, PP = 0.99), and the monophyly of the nemasomatid Nemasoma C.L. Koch, 1847 and Thalassisobates Verhoeff, 1908 was also recovered (BS = 94%, PP = 1.0). The monophyly of the nemasomatid genera Antrokoreana and (Nemasoma + Thalassisobates) was not elucidated, but nonetheless, the obtained phylogenies failed to resolve the basal nodes and phylogenetic relationships among Antrokoreana, (Nemasoma + Thalassisobates) and parajuloidean species.

The COI uncorrected p -distance between A. asuwaensis sp. nov. and A. gracilipes was 16.9% (111/658 bp).