Nipponasellus sudzukhensis Sidorov 2023, spec. nov.
Creators: name: Sidorov, Dmitry
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Isopoda
Asellidae
Nipponasellus
Nipponasellus sudzukhensis

description: Nipponasellus sudzukhensis spec. nov.
Figs 4A, B, 5A–D, 6–9, 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): 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. 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. 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, 5A–D) 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, 5A–D, 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, 5A–D, 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) sub-quadrate with fine setae on apex. Labium sub-triangular, split almost one-third, outer lobes rounded and tapered proximally. Mandibles (Figs 6C, D) 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) 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) 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) 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) 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) 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, 9A–D) 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) 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) 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) 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) 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).
description: Published as part of 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, pp. 342-374 in Zootaxa 5357 (3) on pages 351-358, DOI: 10.11646/zootaxa.5357.3.2, http://zenodo.org/record/10061379