Nipponasellus sudzukhensis, Sidorov, 2023

Sidorov, Dmitry, 2023, Trans-Japan Sea land-bridge disjunction: A case of vicariance in the subterranean genus Nipponasellus (Crustacea, Isopoda, Asellidae) in a largescale biogeographical context, Zootaxa 5357 (3), pp. 342-374 : 351-358

publication ID	https://doi.org/ 10.11646/zootaxa.5357.3.2
publication LSID	lsid:zoobank.org:pub:0ADD6DD7-153F-4ABF-BD89-533ACBA9F3C8
DOI	https://doi.org/10.5281/zenodo.10063688
persistent identifier	https://treatment.plazi.org/id/AD104235-78DB-488B-B036-3BF5BD884D5D
taxon LSID	lsid:zoobank.org:act:AD104235-78DB-488B-B036-3BF5BD884D5D
treatment provided by	Plazi
scientific name	Nipponasellus sudzukhensis
status	sp. nov.

Treatment

Nipponasellus sudzukhensis spec. nov.

Figs 4A, B View FIGURE 4 , 5A–D View FIGURE 5 , 6–9 View FIGURE 6 View FIGURE 7 View FIGURE 8 View FIGURE 9 , ESupplement4

Diagnosis (both sexes): Body flattened dorsoventrally, lateral margins subparallel, lateral expansion of pereonites 1–7 and pleotelson colored with a light brown semitransparent rim. Head sub-trapezoidal, about as long as broad. Dorsal and ventral surface of body, and limbs covered with minute scales of irregular shape. Eyes absent. Antennula length ca. 50% of antennal podomeres length. Antenna length ca. 60% of total body length. Pereopods 1–7 slightly increasing in length towards posterior pairs (except pereopod 4, somewhat slender). Pleopod 2 endopodite in males of primitive type. Uropod short, about half length of pleotelson. Color creamy white. Body length 4.6–6.0 mm (♀♀), 5.5 mm (♁♁).

Etymology: Species named ‘ sudzukhensis ’ (Latin), an adjective that refers to the Sudzukhe River (known today as Kievka), where it was collected.

Bionomics (see map, Fig. 1 View FIGURE 1 ): Nipponasellus sudzukhensis , spec. nov. is a phreatobite that lives in groundwater near the confluence of the Lazovka, Kievka and Pasechnaya Rivers in the foothills of the southwestern slope of the Sikhote-Alin Ridge. Known only from the type locality. Ecology is mostly unknown, but it was accompanied by the following stygobiont fauna: Asellus (A.) primoryensis Henry & Magniez, 1993 ( Isopoda , Asellidae ), Mackinia sp. ( Isopoda , Janiridae ), Pseudocrangonyx kseniae Sidorov, 2012 , and P. sympatricus Sidorov & Gontcharov, 2013 ( Amphipoda , Pseudocrangonyctidae ), Paramoera (G.) myslenkovi Sidorov, 2010 ( Amphipoda , Pontogeneiidae ).

Material examined: Holotype: male, 5.5 mm, X54657/Cr-2475-FEFU, Russia, Primorsky Krai, Lazovsky District, ca. 3 km E of Lazo, Kievka River (Code: 3Lazo), 43°22.160’ N 133°55.485’ E (altitude 217 m a.s.l.), groundwaters, 1.2 m depth, rocks, pebbles, fine-grained sand, detritus, woody debris, riffle, steep riverbank, 3 Aug. 2009, coll. D. Sidorov, K. Semenchenko. GoogleMaps Paratypes: 11 females (2 6.0 mm, 9 4.6 mm), 18 juv. ca. 2.5 mm , 16 juv. ca. 1.5 mm, X54658/Cr-2476-FEFU, same data as holotype. GoogleMaps Material for SEM: Male 5.5 mm, female 5.0 mm, same data as holotype (extra specimen, not included to the type series).

Description (holotype X54657/Cr-2475 and specimen used for SEM): Body ( Figs 4A, B View FIGURE 4 , 5A–D View FIGURE 5 ) elongate and flattened dorsoventrally, ca. 4.6 times longer as wide, lateral margins subparallel to each other and bearing fine simple setae; color creamy white in alcohol; head sub-trapezoidal with frontal margin concave, without posterolateral expansion, about as long as broad, post-mandibular lobes blunt, each with 3 setae; lateral expansion of pereonites 1–7 rounded, colored with a light brown semitransparent rim, each with 2 stiff setae dorsally, pereonites 1–4 directed slightly anteriorly, pereonite 5 with evenly rounded lateral margins, pereonites 6 and 7 sub-similar, with slightly concave distal margins, pereonite 7 the longest; coxopodites well developed, margins not visible from above; pleon 2-segmented; pleotelson oblong, ca. 0.3 times longer as wide and 25% of total body length, with median convexity on posterior margin, lateral margins evenly rounded, setiferous; paired genital papilla located sub-laterally on sternite of pereonite 7, rather large, a little longer than protopodite of pleopod 1; sternal epithelium (blisters) on ventral surface of pereonites 1–7 present.

Antennula ( Figs 4A, B View FIGURE 4 , 5A–D View FIGURE 5 , 4 View FIGURE 4 ) length ca. 50% of antennal podomeres length; articles 1–3 length relations: 1: 0.8: 0.3, article 1 swollen, article 2 with 1 broom seta at inferodistal angle; flagellum length ca. 0.5 times of podomeres length, of 6 articles, successive articles shorter, distal 4 articles with one minute aesthetasc, each with one seta. Antenna ( Figs 4A, B View FIGURE 4 , 5A–D View FIGURE 5 , 4 View FIGURE 4 ) length ca. 60% of total body length; articles 2–6 length relations 0.2: 0.25: 0.25: 0.7: 1, article 5 with a group of short seta at anterodistal angle, article 6 with 2 broom setae and cluster of simple setae of different lengths on distal margin; flagellum length 70% of total antenna length, composed of 29 articles.

Labrum ( Fig. 6E View FIGURE 6 ) sub-quadrate with fine setae on apex. Labium sub-triangular, split almost one-third, outer lobes rounded and tapered proximally. Mandibles ( Figs 6C, D View FIGURE 6 ) sub-equal, with 4-cuspidate pars incisiva (incisor) and 5-cuspidate left lacinia mobilis, setal row of 3–4 serrate and 5–6 plumose stiff setae; palp 3-segmented, ca. twice shorter than mandibular corpus, article 1 with 1 short distal seta, article 2 as long as article 1, with a row of 4 simple medial setae, article 3 paddle-shaped, with a row of 7 simple setae. Maxillula ( Fig. 6F View FIGURE 6 ) inner plate with 5 apical pappose setae; outer plate with 12 serrate robust setae and 1 simple thin seta, 1 simple seta sub-apically on lateral margin, 1 very long simple seta on ventral face. Maxilla ( Fig. 6G View FIGURE 6 ) inner plate longer than outer plate, sharply rounded, sub-triangular, with longer row of 8 setae (4 serrate and 4 simple setae apically), and with double oblique rows of 16 and 5 thin simple setae respectively; lateral and middle plates with 17 simple and 11 striated setae, respectively. Maxilliped ( Fig. 6H View FIGURE 6 ) basal endite broad, apex triangular and reaching tip of palp article 3, about twice longer than wide, with 5 bulbous recurved coupling hooks at distomesial margin, about 20% wider than palp article 2 width, with 20 pappose stiff setae distally, 9 simple slender setae in oblique row and with numerous short simple setae sub-apically on ventral surface; palp article 1 shortest, 3 times as wide as long; article 2 sub-rectangular, ca. 0.3 times shorter than article 4; articles 3–5 length relations: 0.6: 1: 0.4, with a few setae along outer margin, densely setose along inner margin; apex of epipodite sub-square, not pointed, with sparse setae along lateral margin.

Pereopods 1–7 ( Figs 7A–G View FIGURE 7 ) sub-similar in construction, slightly increasing in length towards posterior pairs (except pereopod 4, which is somewhat slender); pereopods 2–7 with 1 denticle and 1 seta along dactylus inner margin. Pereopod 1 length ca. 25% of body length; basis slender, ca. 15% longer than propodus, with 2 and 4 short setae on superior and inferior margins, respectively; ischium length 53% of basis length; merus sub-trapezoidal, dilated distally with moderately curved superior margin bearing 2 stiff setae on distal-superior angle, merus inferior margin with sparse short setae; carpus poorly developed, sub-quadrate, with 1 short stiff seta at distal-superior angle and 2 short stiff and 1 thin setae along inferior margin; propodus unicuspidate, slender, oblong, ca. 3.0 times as long as wide, superior margin as long as palm, both margins slightly convex, palmar margin armed with 6 stiff simple setae and 3 thin setae, ca. half of palmar edge with pilosity pattern; dactylus curved, 0.5 times shorter than palm, with 6 denticles (one of which strong) along inferior margin and with 5 simple setae along superior margin, claw length 30% of total dactylus length, with 1 basal seta. Pereopod 2 ca. 10% longer than pereopod 1; basis–dactylus length relations: 1: 0.6: 0.4: 0.7: 0.7: 0.3; merus sub-trapezoidal, dilated distally with moderately curved superior margin bearing 2 stiff short setae on distal-superior angle; propodus somewhat longer than carpus, with biungulate dactylus; claw about half as long as dactylus length. Pereopods 3–7 slender, similar to pereopod 2.

Pleopod 1 ( Figs 8A, B View FIGURE 8 ) protopodite sub-rectangular, tapered distally, as wide as long, about 50% of exopodite length, with 2 denticulate coupling hooks on medial margin; exopodite broad, rounded sub-rectangular, about 1.6 times as long as wide, without concavity on lateral margin, with 12 short simple setae extending from lateral to terminal margins. Pleopod 2 ( Figs 8C View FIGURE 8 , 9A–D View FIGURE 9 ) protopodite sub-quadratic, clearly tapered distally, as long as wide, with a pattern of cuticular scales; exopodite ca. twice shorter than protopodite, article 1 sub-rectangular, with 1 simple seta on lateral margin, terminal article rounded, catch lobe moderately developed, with 3 plumose and 1 simple on medial, and 2 setae on lateral margins, respectively; endopodite massive, crescent, as long as protopodite, tapered distally, ornamented with sparse finger-like (or ctenoid) cuticular scales close to terminal end, basal spur slender, long, length ca. 50 % of endopodite length, ‘crypte’ incomplete, ‘cannula’ distinct, immersed in ctenoid (i.e., comb-like margined) cuticular scales and delineated circumferentially by an edge of ‘soft limbus’. Pleopod 3 ( Fig. 8D View FIGURE 8 ) exopodite semicircular, with almost rectilinear medial and rounded lateral margins, 2.2 times as long as wide, divided by oblique line into two sub-equal parts, terminal and lateral margins fringed with sparse simple setae; endopodite oblong, sac-like, length ca. 70% of exopodite length. Pleopod 4 ( Fig. 8E View FIGURE 8 ) exopodite sub-ovoid, 2.0 times as long as wide, terminal and lateral margins fringed with numerous minute hairs, respiratory area surface ca. 25% of exopodite surface; endopodite length ca. 90% of exopodite length. Pleopod 5 ( Fig. 8F View FIGURE 8 ) exopodite elongate, ovoid, 2.3 times as long as wide, respiratory area surface ca. 35% of exopodite surface, linea area beginning and ending as slightly curved suture from internal to terminal margin; endopodite elongate, ovoid, longer than wide. Uropod ( Fig. 8G View FIGURE 8 ) short, about half length of pleotelson; peduncle a little longer than both rami, length relations: 1: 0.7: 0.4.

Variation: Not observed.

Sexual dimorphism: Females are generally similar to males except for being slightly larger. Collected females did not have developed marsupial plates (oostegites). Pereopod 1 propodus is not sexually dimorphic; male and female pereopods are similar. Pereopod 4 not sexually dimorphic. Female pleopod 2 sub-triangular, tapered distally, apex and distal half of lateral margin with 2 minute setae.

Taxonomic comments: Nipponasellus sudzukhensis spec. nov., with a moderately broad body, closely fitting pereonites, antennula and antenna with 6 and 29 articles in males, uropods shorter than pleotelson and a body length of up to 6 mm, most closely resembles N. hubrichti (Matsumoto, 1956) , but can be distinguished by (character states of N. hubrichti in brackets): mandibular palp 3-articulated (reduced, 1-articulated); length of antenna in males about 60% of total body length (up to 80%) (see Table 2 View TABLE 2 ).