Pseudocrangonyx uenoi, Tomikawa & Abe & Nakano, 2019

Tomikawa, Ko, Abe, Yuji & Nakano, Takafumi, 2019, A New Stygobitic Species of the Genus Pseudocrangonyx (Crustacea: Amphipoda: Pseudocrangonyctidae) from Central Honshu, Japan, Species Diversity 24, pp. 259-266 : 259-266

publication ID	https://doi.org/ 10.12782/specdiv.24.259
publication LSID	lsid:zoobank.org:pub:555E885D-53B3-46E0-A3A5-3B66E5714620
persistent identifier	https://treatment.plazi.org/id/2AA7A4D0-AAA8-410E-99C6-753D7145CFF6
taxon LSID	lsid:zoobank.org:act:2AA7A4D0-AAA8-410E-99C6-753D7145CFF6
treatment provided by	Felipe
scientific name	Pseudocrangonyx uenoi
status	sp. nov.

Treatment

Pseudocrangonyx uenoi sp. nov.

( Figs 1–5 View Fig View Fig View Fig View Fig View Fig )

Pseudocrangonyx sp. 3 : Tomikawa et al. 2016: fig. 10; Zhao and Hou 2017: table 1, fig. 8; Lee et al. 2018: table 1, fig. 10; Tomikawa and Nakano 2018: fig. 11; Copilaş-Ciocianu et al. 2019: figs 2, 3.

Diagnosis. Antennal sinus with rounded angle; eyes completely absent; pereonites with short dorsal setae; urosomite 1 without ventral robust seta; dorsal margin of urosomite 3 lacking setae; sternal gill absent; antenna 1 0.4–0.5 times as long as body length; flagellar articles of antenna 2 with calceoli; mandible, palp article 3 slightly longer than article 2; maxilla 1, inner plate with 2–3 setae; maxilla 2, inner plate with oblique inner row of 2 setae; gnathopods 1 and 2, carpi without serrate robust setae on posterodistal corners; palmar margins of propodi of gnathopods 1 and 2 with 8–9 and 10–11 robust setae, respectively; pleopods, peduncles lacking marginal setae and inner margin of inner rami without bifid setae; uropod 1, inner ramus 1.6–2.0 times as long as outer ramus, inner margin of former with 3 robust setae, basal part with 1–2 slender setae, outer ramus with 1 marginal robust seta; uropod 2, inner ramus 1.2–1.5 times as long as outer ramus, its inner and outer margins with 0–2 and 1 robust setae, respectively, outer ramus with 0–1 inner and 1 outer marginal robust setae; uropod 3, terminal article 0.2–0.3 times as long as proximal article; and telson 1.3 times as long as wide, cleft for 17.1–20.4%.

Material examined Holotype: female 4.0 mm, KUZ Z2514 View Materials , from Samenokōmoriana Cave (35.20445°N, 136.34383°E), Taga town, collected by T. Nakano and K. Tomikawa on 28 May 2017 GoogleMaps . Paratypes (5 specimens): male 4.3 mm, KUZ Z2515, female 4.6 mm, KUZ Z2516, data same as for holotype; male 2.4 mm, KUZ Z1963, from Kawachi Wind Cave (Kawachi Fuketsu Cave), Taga town, on 9 October 2009; female 2.9 mm, KUZ Z1964, from Samenokōmoriana Cave, Taga town, on 8 September 2008; female 2.1 mm, KUZ Z1965 from Gongen Cave, Taga town, on 30 September 2009.

Description. Female (KUZ Z2514, 4.0 mm). Head ( Fig. 1 View Fig ) with short rostrum; lateral cephalic lobe rounded; antennal sinus with rounded angle; eyes absent. Pereonites 1–7 with short dorsal setae ( Fig. 1 View Fig ); posterolateral margin of pereonites 6 and 7 each with 1 seta ( Fig. 1 View Fig ). Dorsal margin of pleonites 1–3 with 4, 4, and 5 setae, respectively ( Fig. 2A–C View Fig ). Posterior margin of epimeral plate 1 with 2 setae, posteroventral corner not produced with 1 seta ( Fig. 2D View Fig ); ventral and posterior margins of plate 2 with 1 and 3 setae, respectively, posteroventral corner not produced, with 1 seta ( Fig. 2E View Fig ); ventral and posterior margins of plate 3 with 1 and 2 setae, respectively, posteroventral corner rounded, with 1 seta ( Fig. 2F View Fig ). Ventral margin of urosomite 1 without setae ( Fig. 1 View Fig ); dorsal margin of urosomites 1 and 2 with 2 and 4 slender setae, respectively ( Fig. 2G, H View Fig ), dorsal margin of urosomite 3 lacking setae ( Fig. 1 View Fig ).

Antenna 1 ( Fig. 2I View Fig ) 0.5 times as long as body length, peduncular articles 1 to 3 in length ratio of 1.0: 0.7: 0.5; accessory flagellum 2-articulate; primary flagellum 1.3 times as long as peduncular articles 1–3 combined, 11-articulate, 1 aesthetasc on some articles. Antenna 2 ( Fig. 2J View Fig ) 0.7 times as long as antenna 1; peduncular articles without calceoli; flagellum 0.4 times as long as peduncular articles 4 and 5 combined, consisting of 5 articles, first 2 of which with calceolus ( Fig. 2K View Fig ).

Upper lip ( Fig. 2L View Fig ) with rounded anterior margin, bearing fine setae. Mandibles ( Fig. 2M–O View Fig ) with left and right incisors both 5-dentate; left lacinia mobilis 5-dentate, right lacinia bifid, bearing many teeth; molar process weakly triturative, molar of right mandible with accessory plumose seta; accessory setal rows of left and right mandibles both with 4 weakly pectinate setae; palp 3-articulate, article 3 length 1.1 times as long as article 2 with 1 A-, about 9 D-, and 4 E-setae. Lower lip ( Fig. 2P View Fig ) with broad outer lobes, mandibular process of outer lobe rounded apically; inner lobes indistinct. Maxilla 1 ( Fig. 2Q View Fig ) with inner and outer plates, and palp; inner plate subovate, its medial margin with 3 plumose setae; outer plate subrectangular with 7 serrate teeth apically; palp 2-articulate, longer than outer plate, article 1 lacking marginal setae, article 2 with 2 robust setae and 1 slender seta apically, and 1 slender seta subapically. Maxilla 2 ( Fig. 2R View Fig ) with oblique inner row of 2 plumose setae on inner plate. Maxilliped ( Fig. 2S View Fig ) with inner and outer plates, and palp; inner plate with 3 apical and 1 subapical robust setae; outer plate with 1 apical plumose seta, and 2 robust and some slender setae on medial margin; palp 4-articulate, medial margin of article 2 lined with setae.

Gnathopod 1 ( Fig. 3A View Fig ) with subquadrate coxa bearing 2 setae on anterodistal corner of coxa, width 2.2 times as long as depth; anterodistal submargin of basis with short seta, posterior margin of basis with long setae; posterodistal corner of carpus with weakly serrate slender setae ( Fig. 3B View Fig ), lacking serrate robust setae; propodus stout, ovate, palmar margin with 4 lateral and 5 medial robust setae, some distally notched ( Fig. 3C View Fig ); posterior margin of dactylus dentate ( Fig. 3C View Fig ). Gnathopod 2 ( Fig. 3D View Fig ) with subquadrate coxa bearing setae on its anterodistal and posteroventral corners, width 1.5 times as long as depth; basis with short seta on anterodistal submargin and long setae on posterior margin; posterodistal corner of carpus without serrate robust setae; propodus weakly slender than that of gnathopod 1, with 3 lateral and 7 medial robust setae along palmar margin ( Fig. 3E View Fig ); posterior margin of dactylus dentate ( Fig. 3E View Fig ). Pereopod 3 ( Fig. 3F View Fig ) with subquadrate coxa bearing setae on its anterodistal and posteroventral corners, width 1.5 times as long as depth; anterior and posterior margins of basis with short and long setae, respectively; merus, carpus, and propodus in length ratio of 1.0: 0.8: 0.8; anterior and posterior margins of dactylus with 1 and 2 setae, respectively ( Fig. 3G View Fig ). Pereopod 4 ( Fig. 3H View Fig ) with coxa bearing setae on its anterodistal and posteroventral corners, width 1.7 times as long as depth; anterior and posterior margins of basis with short and long setae, respectively; merus, carpus, and propodus in length ratio of 1.0: 0.8: 0.9; anterior and posterior margins of dactylus each with 2 setae ( Fig. 3I View Fig ). Pereopod 5 ( Fig. 3J View Fig ) with weakly bilobed coxa bearing setae on anterior and posterior lobes; anterior and posterior margins of basis with setae; merus, carpus, and propodus in length ratio of 1.0: 0.7: 0.8; anterior and posterior margins of dactylus each with 1 seta ( Fig. 3K View Fig ). Pereopod 6 ( Fig. 3L View Fig ) with coxa bearing concave lower margin, posteroproximal corner with 1 seta; anterior and posterior margins of basis with short setae; merus, carpus, and propodus in length ratio of 1.0: 0.8: 0.9; anterior and posterior margins of dactylus each with 1 seta ( Fig. 3M View Fig ). Pereopod 7 ( Fig. 3N View Fig ) with subtriangular coxa, posteroproximal corner of coxa with 1 seta; anterior and posterior margins of basis with short setae; merus, carpus, and propodus in length ratio of 1.0: 0.9: 1.0; anterior and posterior margins of dactylus with 3 and 1 setae ( Fig. 3O View Fig ).

Brood plates slender on gnathopod 2 and pereopods 3–5.

Coxal gills ( Fig. 1 View Fig ) on gnathopod 2 and pereopods 3–6; sternal gills absent.

Peduncles of pleopods 1–3 ( Fig. 4A, C, D View Fig ) marginally bare, each with paired retinacula ( Fig. 4B View Fig ), outerdistal corners of pleopods 1–3 with 2, 1, and 1 short setae, respectively; inner basal margin of inner ramus without bifid setae.

Uropod 1 ( Fig. 4E View Fig ) with 1 basofacial slender seta on peduncle; peduncle 1.1 times as long as inner ramus; inner ramus 2.0 times as long as outer ramus, inner margin of inner ramus with 3 robust setae, outer margin bare, basal part with 2 slender setae; outer ramus with 1 marginal robust seta. Uropod 2 ( Fig. 4F View Fig ) with peduncle 1.1 times as long as inner ramus; inner ramus 1.5 times as long as outer ramus, its outer margin with 1 seta; outer ramus with 1 outer marginal robust seta. Uropod 3 ( Fig. 4G View Fig ) with peduncle 0.4 times as long as outer ramus; inner ramus absent; outer ramus 2-articulate, proximal article with robust setae, terminal article 0.3 times as long as proximal article, short- er than distal robust setae on proximal article, with 3 distal setae ( Fig. 4H View Fig ).

Telson ( Fig. 4I View Fig ) length 1.3 times as long as wide, cleft for 20.4% of length, each telson lobe with 2 lateral long penicillate setae, 1 apical robust seta, and 1 apical penicillate seta.

Male (KUZ Z2515, 4.3 mm). Antenna 1 ( Fig. 5A View Fig ) 0.5 times as long as body length, primary flagellum 13-articulate. Antenna 2 ( Fig. 5B View Fig ) 0.6 times as long as antenna 1, peduncular articles without calceolus; flagellum 0.5 times as long as peduncular articles 4 and 5 combined, 4-articulate, articles 1–3 each with calceolus.

Mandibular palp article 3 length 1.3 times as long as article 2. Maxilla 1 with 2 plumose setae on its medial margin.

Gnathopod 1 with 6 lateral and 2 medial robust setae on palmar margin ( Fig. 5C, D View Fig ). Gnathopod 2 with 4 lateral and 7 medial robust setae on palmar margin ( Fig. 5E, F View Fig ).

Uropod 1 ( Fig. 5G View Fig ) with inner ramus 1.6 times as long as outer ramus, bearing 1 slender seta on basal part. Uropod 2 ( Fig. 5H, I View Fig ) with inner ramus 1.2 times as long as outer ramus, its inner and outer margins with 1 simple and 1 weakly serrate robust setae, respectively, distal part with 2 serrate and 4 simple robust setae and 1 slender seta; inner and outer margins of outer ramus with 1 simple and 2 serrate robust setae, respectively, distal part with 1 weakly serrate and 4 simple robust setae. Uropod 3 ( Fig. 5J View Fig ) with more robust setae on proximal article of outer ramus than that of female, terminal article 0.2 times as long as proximal article. Telson cleft for 17.2% of length.

Variation. Antenna 1 0.4 times as long as body length; antenna 2 0.6 times as long as antenna 1; maxilla 1 inner plate with 2 plumose setae on its medial margin; telson cleft for 17.1% (female 4.6 mm, KUZ Z2516).

Distribution. The species is known from limestone caves in Taga Town, Shiga Prefecture, Japan. Specimens were collected from small pools and streams in the caves.

DNA sequences. In total, 9 sequences of the present paratypes were determined by Tomikawa et al. (2016): KUZ Z1963 View Materials , 2 View Materials sequences—28S ( LC171488 View Materials ; 1297 bp), and H3 ( LC171489 View Materials ; 328 bp); KUZ Z1964 View Materials , 4 View Materials sequences— 28S ( LC171491 View Materials ; 1297 bp) H3 ( LC171493 View Materials ; 328 bp), COI ( LC171492 View Materials ; 658 bp), and 16S ( LC171490 View Materials ; 416 bp); and KUZ Z1965 View Materials , 3 View Materials sequences—28S ( LC171495 View Materials ; 1297 bp), H3 ( LC171496 View Materials ; 328 bp), and 16S ( LC171494 View Materials ; 416 bp) .

Etymology. The specific name is dedicated to the late Professor Masuzo Uéno, who was the past director of the now defunct Otsu Hydrobiological Station of Kyoto University in Shiga Prefecture, and greatly contributed to the Pseudocrangonyx systematics.

Remarks. A previous phylogenetic study ( Lee et al. 2018) showed that Pseudocrangonyx uenoi sp. nov. formed a monophyletic lineage with P. daejeonensis Lee, Tomikawa, Nakano, and Min, 2018 , which was described from the interstitial water in the Korean Peninsula. Both species have a small body size that is shorter than 5 mm; eyes that are completely absent; urosomite 1 without ventral setae; carpi of gnathopods 1 and 2 without serrate robust setae on the posterodistal corners; and inner rami of pleopods without bifid setae on its inner margins. However, these characteristics may not to be synapomorphies between P. uenoi sp. nov. and P. daejeonensis because they are also shared with the other Pseudocrangonyx species ( Tomikawa et al. 2016).

Pseudocrangonyx uenoi sp. nov. can be clearly differenti- ated from P. daejeonensis by female antenna 2 with calceoli (versus without calceoli in P. daejeonensis ); the lacinia mobilis of the left mandible being 5-dentate (versus 4-dentate); a peduncle of pleopod 1 without marginal setae (versus with a marginal seta); a peduncle of pleopod 3 with a seta on the outerdistal corner (without setae); pleopodal rami being up to 5-articulate (versus less than 5-articulate); the terminal article of uropod 3 being short, not reaching the tips of the robust setae on the distal part of the proximal article of uropod 3 (versus long, reaching past the tips of the robust setae); and the telson cleft being 17.1–20.4% (versus 8%) of its length.

Pseudocrangonyx uenoi sp. nov. also resembles P. komaii Tomikawa and Nakano, 2018 from central Japan in its absent eyes, its ventral setae being on urosomite 1, its posterodistal corners of gnathopods 1 and 2 carpi without serrate robust setae, its marginal setae being on the pleopodal peduncle, its bifid setae being on the inner rami of pleopods, its having calceoli on antenna 2 in both sexes, and its short terminal article of uropod 3 not reaching the tip of the robust setae on the distal part of the proximal article. The new species can be distinguished from P. komaii by the absence of calceoli on peduncular article 5 of antenna 2 (versus present in P. komaii ), the pleopodal rami being up to 5-articulate (versus up to 8-articulate), the terminal article of uropod 3 being 0.2–0.3 (versus 0.1) times as long as the proximal article of uropod 3, and the telson cleft being 17.1–20.4% (versus 6.8%) of its length.