Pseudocrangonyx asuwaensis, Shintani & Umemura & Nakano & Tomikawa, 2023

Shintani, Aki, Umemura, Shinya, Nakano, Takafumi & Tomikawa, Ko, 2023, A new species of the genus Pseudocrangonyx (Crustacea: Amphipoda: Pseudocrangonyctidae) from subterranean waters of Japan, Zootaxa 5301 (3), pp. 383-396 : 385-394

publication ID	https://doi.org/ 10.11646/zootaxa.5301.3.4
publication LSID	lsid:zoobank.org:pub:B7A65F4C-DD8D-48D7-A3C0-058D34DE212F
DOI	https://doi.org/10.5281/zenodo.8030534
persistent identifier	https://treatment.plazi.org/id/CB49C31C-5ACB-4BE0-A732-296952ADE19A
taxon LSID	lsid:zoobank.org:act:CB49C31C-5ACB-4BE0-A732-296952ADE19A
treatment provided by	Plazi
scientific name	Pseudocrangonyx asuwaensis
status	sp. nov.

Treatment

Pseudocrangonyx asuwaensis sp. nov.

( Figs 1–6 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 )

Material examined. Holotype: female 5.4 mm ( KUZ Z4464 View Materials ), Nanatsuoguchi , Mt. Asuwa, Fukui, Japan (36.055822°N, 136.197178°E), collected by K. Tomikawa and S. Umemura on 29 March 2018 GoogleMaps . Paratypes: three females 4.9 mm ( KUZ Z4465 View Materials ), 4.6 mm ( KUZ Z4466 View Materials ), 4.0 mm ( KUZ Z4467 View Materials ), data same as for holotype GoogleMaps ; two females 8.3 mm ( KUZ Z4371 View Materials ), 8.9 mm ( KUZ Z4468 View Materials ), locality same as for holotype, collected by S. Umemura on 10 November 2017 GoogleMaps .

Diagnosis. Female. Head without eyes; antennal sinus with subquadrate angle. Pereonites 1–7 without long marginal setae. Urosomite 1 without setae on ventral margin. Antenna 1 0.6 times as long as body length. Antenna 2 without calceoli. Mandibular palp article 3 longer than article 2. Maxilla 1 inner plate with 3 setae. Maxilla 2 inner plate with oblique inner row of 5 plumose setae. Gnathopod 1 with or without robust serrate setae on posterodistal corner of carpus. Gnathopod 2 with robust serrate setae on posterodistal corner of carpus. Sternal gills absent. Uropods 1 and 2 inner ramus each with 3 robust setae on inner margin. Uropod 3 terminal article 0.3 times as long as proximal article, longer than distal robust setae on proximal article. Telson length 1.2 times as long as wide, cleft for 10% of length.

Description of female (holotype, KUZ Z4464). Head ( Fig. 6A View FIGURE 6 ) without eyes, rostrum short; lateral cephalic lobe weakly produced, rounded; antennal sinus with subquadrate angle. Pereonites 1–7 with small dorsal setae, lacking long marginal setae; pereonites 5–7 with 1, 1 and 3 setae on posterolateral margins, respectively. Pleonite 1–3 ( Figs 2A–C View FIGURE 2 , 6B View FIGURE 6 ) with 12, 10 and 13 setae on dorsal margins, respectively; epimeral plate 1 ( Fig. 5A View FIGURE 5 ) with robust seta on ventral submargin, 4 setae on posterior margin, and robust seta on posterodistal corner; epimeral plates 2 and 3 ( Fig. 5B, C View FIGURE 5 ) each with 3 robust setae on ventral margin, 4 setae on posterior margin, and seta on posterodistal corner. Urosomite 1 ( Fig. 2D View FIGURE 2 ) with 3 pairs of robust setae on dorsal margin, lacking setae on ventral margin; urosomite 2 ( Fig. 2E View FIGURE 2 ) with two pairs of robust setae; urosomite 3 ( Fig. 2F View FIGURE 2 ) without dorsal setae.

Antenna 1 ( Fig. 2G View FIGURE 2 ) 0.6 times as long as body length; length ratio of peduncular articles 1–3 in 1.0: 0.8: 0.5, peduncular article 1 with robust seta on posterior margin; accessory flagellum 2-articulate; primary flagellum 16- articulate, 1.4 times as long as combined length of peduncular articles 1–3, 1 aesthetasc on some articles. Antenna 2 ( Figs 2H View FIGURE 2 , 6C View FIGURE 6 ) 0.6. times as long as antenna 1; peduncular articles 3–5 with robust setae on medial faces, peduncular articles 4 and 5 of the same length; flagellum 7-articulate, with 1 aesthetasc on each article, calcioli absent.

Upper lip ( Fig. 2I View FIGURE 2 ) with rounded anterior margin. Mandibles ( Fig. 2J–L View FIGURE 2 ) with left and right incisors 5-dentate; left lacinia mobilis comprising five teeth, right lacinia mobilis trifurcate with minute serration; molar process triturative with plumose seta; palp consisting of three articles, length ratio of articles 1–3 in 1.0: 2.8: 3.5, article 1 bare, article 2 with 6 setae on ventral margin, article 3 with 2 A-, 11 D-, and 3 E-setae. Lower lip ( Fig. 2M View FIGURE 2 ) with broad, rounded outer lobes; inner lobes indistinct. Maxilla 1 ( Fig. 2N, O View FIGURE 2 ) inner plate with 3 plumose setae; outer plate with 7 serrate teeth apically; palp comprising 2 articles, article 2 with 4 apical and 1 subapical robust setae. Maxilla 2 ( Fig. 2P View FIGURE 2 ) with oblique inner row of 5 plumose setae on inner plate. Maxilliped ( Fig. 3A–C View FIGURE 3 ) inner plate with 2 apical and 2 subapical robust setae; outer plate not exceeding distal end of palp article 1; palp 4-articulate, palp article 2 with setae on medial margin, article 4 with distinct nail.

Gnathopod 1 ( Fig. 3D, E View FIGURE 3 ) coxa rectangle with setae on anterior to ventral margins; basis with long setae on posterior margin, lacking setae on anterior margin; carpus subtriangular, length 0.7 times width with serrate robust seta on posterodistal corner; propodus ovate, length 1.5 times width, palmar margin with 6 medial and 4 lateral robust setae; dactylus with dentate posterior margin. Gnathopod 2 ( Figs 3F, G View FIGURE 3 , 6E, F View FIGURE 6 ) coxa subquadrate with setae on anterior to ventral margins; basis with short seta on anterodistal corner and long setae on posterior margin; carpus elongate, length 1.4 times width, with 2 serrate robust setae on posterodistal corner; propodus subrectangular, length 1.6 times width, palmar margin with 5 medial and 4 lateral robust setae.

Pereopods 3 ( Fig. 4A, B View FIGURE 4 ) coxa subrectangular; basis with short setae on anterior margin and long setae on posterior margin; length ratio of merus, carpus and propodus in 1.0: 0.8: 0.9; posterior margin of dactylus with 2 setae. Pereopods 4 ( Fig. 4C View FIGURE 4 ) coxa subrectangular; basis with short setae on anterior margin and long setae on posterior margin; length ratio of merus, carpus and propodus in 1.0: 0.9: 0.9; posterior margin of dactylus with seta. Pereopod 5 ( Fig. 4D View FIGURE 4 ) coxa bilobed with setae on anterior and posterior lobes; basis with robust setae on anterior margin and slender setae on posterior margin; length ratio of merus, carpus and propodus in 1.0: 0.8: 0.9; anterior margin of dactylus with 2 setae. Pereopod 6 ( Fig. 4E View FIGURE 4 ) coxa bilobed with setae on anterior and posterior lobes; basis with robust setae on anterior and posteroproximal margins; length ratio of merus, carpus and propodus in 1.0: 0.9: 0.9; anterior margin of dactylus with 2 setae. Pereopod 7 ( Fig. 4F View FIGURE 4 ) coxa subtriangular with setae on anterior margin and posterodistal part; basis with robust setae on anterior and posteroproximal margins; length ratio of merus, carpus and propodus in 1.0: 1.0: 1.1; dactylus with 2 setae on anterior margin.

Coxal gills ovate with stalk, on gnathopod 2 and pereopods 3–6. Sternal gills absent. Brood plates (=oostegites) ( Fig. 3H View FIGURE 3 ) narrow, with marginal setae.

Pleopods 1–3 ( Fig. 5D, E View FIGURE 5 ) peduncles with 2, 2 and 1 setae on lateral margins, respectively, and 2, 2 and 1 setae on outer distal corner of peduncle, inner distal corners with paired retinacula; inner ramus of pleopods 1–3 6-, 5- and 4-articulate, respectively, without bifid plumose setae on inner basal margin; outer ramus of pleopods 1–3 6-, 5- and 4-articulate, respectively.

Uropod 1 ( Fig. 5F View FIGURE 5 ) peduncle with 2 basofacial robust setae; inner ramus 0.8 times as long as peduncle, inner and outer margins with 3 and 1 robust setae, respectively, ventroproximal part with long seta; outer ramus 0.6 times as long as inner ramus, with robust seta. Uropod 2 ( Fig. 5G View FIGURE 5 ) inner ramus 1.5 times as long as peduncle, inner and outer margins with 3 and 2 robust setae, respectively; outer ramus 0.6 times as long as inner ramus, with 2 robust setae. Uropod 3 ( Fig. 5H View FIGURE 5 ) peduncle with robust setae distally; outer ramus 2-articulate, proximal article with robust and slender setae on inner and outer margins, terminal article 0.3 times as long as proximal article, longer than distal robust setae on proximal article, with three distal setae.

Telson ( Fig. 5I View FIGURE 5 ) length 1.2 times as long as wide, cleft for 10% of length, each telson lobe with 2 lateral penicillate setae, 2 apical robust seta, and apical penicillate seta.

Variation. Paratype female (8.9 mm, KUZ Z4468 View Materials ) has maxilla 2 with oblique inner row of seven plumose setae on inner plate, gnathopods 1 and 2 each with three serrate robust setae on posterodistal corner of carpus, and telson length 1.3 times as long as wide, cleft for 7% of length . Paratype female (4.0 mm, KUZ Z4467 View Materials ) lacks robust serrate setae on posterodistal corner of carpus of gnathopod 1 ( Fig. 6D View FIGURE 6 ) .

Molecular phylogenetic analyses. The results of the molecular phylogenetic analyses performed in this study are consistent with those of previous studies ( Lee et al. 2018; Tomikawa & Nakano 2018; Tomikawa et al. 2022) ( Fig. 7 View FIGURE 7 ). Pseudocrangonyx asuwaensis sp. nov. clustered with P. komaii from Gifu Prefecture and Pseudocrangonyx spp. 7 and 8 from Mie Prefecture with high statistical support (BS = 84%, PP = 0.99). This monophyletic group corresponds to clade II ( Tomikawa et al. 2022). Among these four species, P. asuwaensis sp. nov. is sister to the clade comprising the remaining three species.

Etymology. This species is named after its type locality, Mt. Asuwa.

Remarks. Pseudocrangonyx asuwaensis sp. nov. is morphologically most similar to P. elenae Sidorov, 2011 , in having a head without eyes, antenna 1 0.6 times shorter than body length, female antenna 2 without calceoli, mandibular palp article 3 longer than article 2, female gnathopod 2 with robust serrate setae on posterodistal corner of carpus, sternal gills absent, urosomite 1 without ventral robust setae, and cleft telson. However, this new species differs from P. elenae in the following features (features of P. elenae in parentheses): 1) head antennal sinus with subquadrate angle (weakly concave); 2) maxilla 1 inner plate with 3 (5) setae; 3) uropods 1 and 2 inner ramus each with 3 robust setae on inner margin (5 and 4 robust setae, respectively); and 4) uropod 3 terminal article 0.3 (0.05) times as long as proximal article, longer (shorter) than distal robust setae on proximal article. Pseudocrangonyx asuwaensis sp. nov. is distinguished from the phylogenetically related P. komaii in the following features (features of P. komaii in parentheses): 1) female antenna 2 without (with) calceoli; 2) mandible palp article 3 longer than article 2 (almost as long as article 2); 3) maxilla 1 inner plate with 3 (4) setae; 4) female gnathopod 2 with (without) robust serrate setae on posterodistal corner of carpus; and 5) telson cleft for 10% (6.8%) of length.

Our molecular phylogenetic analyses also showed that P. asuwaensis sp. nov. is phylogenetically related to two molecular operational taxonomic units (MOTUs), Pseudocrangonyx spp. 7 and 8 recognized by Yonezawa et al. (2020), from cave groundwaters in Mie Prefecture, Japan. However, the taxonomic status of these MOTUs still remains unclarified due to the small number of their specimens available for examination. Further morphological and molecular phylogenetic analyses based on additional specimens for these units are essential to clarify their taxonomic accounts.