Pseudocrangonyx concavus, Jung & Kim & Kim & Yoon, 2020

Jung, Tae Won, Kim, Jong Guk, Kim, Min-Seop & Yoon, Seong Myeong, 2020, Five new subterranean amphipods of the genus Pseudocrangonyx from Korea (Crustacea, Amphipoda, Pseudocrangonyctidae), ZooKeys 970, pp. 1-50 : 1

Pseudocrangonyx concavus sp. nov. Figs 1 , 2 , 3 , 4

Korean name.

O-mok-nal-gae-dong-gul-yeop-sae-u, new

Type locality.

Hwansangul Cave, Samcheok-si, Gangwon-do, South Korea; 37°20'55"N, 129°04'45"E.

Material examined. Type material. Holotype: 1 female, 9.2 mm, NIBRIV0000862807. Paratypes: 4 specimens, NIBRIV0000872407. All type materials were collected from the type locality on 19 Jan 2001 by YG Choi.

Additional material. 1 female, 8.9 mm, NIBRIV0000872408; 1 male, 5.5 mm, NIBRIV0000872409, collected from the type locality on 13 Jan 2010 by YG Choi.

Etymology.

The specific name originates from the Latin word concavus meaning concave, hollow. This name refers to the shape of posteriorly emarginated ventral margin of epimeral plate 3.

Diagnosis.

Maxilla 1 inner lobe with five plumose setae on apical margin; 2nd palp article with eight robust setae along distomedial and apical margins. Maxilla 2 inner lobe with one oblique row of seven plumose setae on surface; outer lobe apical margin with three plumose setae medially. Pereopod 5 coxa anterior lobe expanded ventrally (1.00 × longer than wide), margin lined with seven simple setae; basis expanded and subrectangular (0.55 × wider than long). Pereopod 6 coxa anterior lobe 0.62 × as long as that of pereopod 5, with one seta only on ventral margin; basis expanded. Sternal gills present from pereonites 2-5 (1+2+1+1 in formulae). Epimeral plate 2 ventral margin with two submarginal setae anteriorly, posterodistal corner slightly notched bearing one elongate setae. Epimeral plate 3 posterodistal corner without notch, rounded, ventral margin with three submarginal setae anteriorly, posteriorly emarginated. Uropod 1 inner ramus with one elongate seta on ventral margin subproximally. Uropod 2 peduncle 0.62 × as long as that of uropod 1.

Description.

Holotype female: Body (Fig. 1A ) approximately 9.2 mm long.

Head (Fig. 1B ) as long as pereonite 1; rostrum reduced, without minute setae; lateral cephalic lobe anteriorly expanded, apex rounded, slightly dilated anteroventrally; antennal sinus not deep; eye absent.

Antenna 1 (Fig. 1C ) 0.51 × as long as body; peduncle 1st-3rd articles length ratio of 1.00: 0.76: 0.40; 1st article stout, with one pair of robust setae on posterior margin; accessory flagellum bi-articulate, last article very reduced, with one pair of aesthetascs distally; flagellum 1.15 × as long as peduncles, composed of 16 articles, calceoli absent, aesthetascs present on the 9th-11th, 13th, 14th, and last articles.

Antenna 2 (Fig. 1D, E ) 0.59 × as long as antenna 1; antennal cone developed, apex rounded; peduncle 4th and 5th articles length ratio of 1.00: 0.89; 4th article margins parallel, 0.27 × wider than long, posterior margin with one row of setae at the middle and one elongate seta subdistally, 5th article 0.75 × wider than 4th article, two calceoli present on medial surface; flagellum composed of eight articles, 1.21 × as long as peduncle 5th article, single calceoli present on 1st, 4th, and 5th articles medially, aesthetascs absent.

Upper lip (Fig. 1F ) anteriorly rounded, apex covered with minute setae, slightly notched.

Lower lip (Fig. 1G ) inner lobes indistinct; outer lobes covered with minute setae; mandibular processes developed.

Mandibles (Fig. 1H, I ) incisor 5-dentate on both sides; lacinia mobilis tri-cuspidate (each finely dentate) on right side and bi-furcate (one 5-dentate and the other not dentate) on left side; four raker setae present on both sides; molar process columnar, triturative, with one plumose seta on right side only; palp tri-articulte; 2nd article convex and with 14 setae medially; 3rd article subfalcate, 1.31 × as long as 2nd article, lined with 19 setae from medial margin to apex.

Maxilla 1 (Fig. 1J ) inner lobe subrhomboid, with five plumose setae on apical margin; outer lobe with seven dentate robust setae; palp bi-articulate, 2nd article apex slightly exceeding apical setae of outer plate, with eight robust setae along distomedial and apical margins, with one oblique row of seven setae subdistally.

Maxilla 2 (Fig. 1K ) inner lobe slightly shorter but wider than outer lobe, with one oblique row of seven plumose setae on surface and two rows of simple setae on apical margin; outer lobe apical margin with three plumose setae medially, also with two rows of simple setae.

Maxilliped (Fig. 1L ) inner lobe subrectangular, with three dentate robust setae on apex and eight plumose setae subapically; outer lobe elongate semicircular, 0.89 × as long as palp 2nd article, with two dentate robust setae and six plumose setae apically; palp composed of four articles; 2nd article with many setae on medial margin; 3rd article slightly dilated distally, 0.60 × as long as 2nd article; 4th article falcate, 0.67 × as long as 3rd article, apical setae 0.67 × as long as 4th article.

Gnathopod 1 (Fig. 2A-C ) coxa subrectangular, 1.52 × wider than long, slightly produced anterodistal corner with five setae marginally, ventral margin slightly convex, with one seta posteriorly, posterior margin humped proximally; basis obtuse trapezoidal, posteriorly expanded, 0.49 × wider than long, lined with elongate simple setae posteriorly, anterior margin obliquely truncated distally, without setae; ischium 0.30 × as long as basis, with small anterior lobe; carpus 0.51 × as long as basis, with one robust seta on anterior margin, carpal lobe not developed, apex rounded with three rastellate setae and many simple or serrate setae; propodus subovate, 1.30 × as long and 1.65 × as wide as basis, with five robust setae laterally along posterior margin distally and ten robust setae medially along posterior margin and palm (all medial setae small, but lateral setae larger and successively increasing distally), palm irregular, finely serrated, defined by largest lateral seta of posterior margin; dactylus as long as palm, inner margin toothed, outer margin with four setae, unguis developed.

Gnathopod 2 (Fig. 1D-F ) as long as gnathopod 1; coxa 1.28 × as long as that of gnathopod 1, 1.19 × wider than long, anterior and ventral margins not produced, rounded, lined with seven setae anteriorly and three setae posteriorly, posterior margin humped proximally; coxal gill present, subovate; oostegite present, narrow, shorter than coxal gill, without marginal setae; basis subtrapezoidal, posteriorly expanded, 0.37 × wider than long, lined with elongate simple setae posteriorly, anterior margin with one seta subdistally; ischium 0.19 × as long as basis, with small anterior lobe; carpus 0.42 × as long as basis, with one pair of robust seta and simple seta on anterior margin, carpal lobe not developed, apex rounded with one rastellate seta and many simple or serrate setae; propodus trapezoidal, 0.98 × as long and 1.42 × as wide as basis, anterior margin slightly convex, posterior margin 0.49 × as long as anterior margin, lined with five clusters of elongate setae, palm irregular, finely serrated, lined with six medial and eight lateral robust setae (palm defined by two unequal setae distally among lateral setae); dactylus as long as palm, inner margin toothed, outer margin with three setae, unguis developed.

Pereopod 3 (Fig. 2G ) coxa rectangular, 1.24 × wider than long, ventral margin with six anterior and three posterior setae, posterior margin slightly humped proximally; coxal gill present, subovate; oostegite present, narrow, shorter than coxal gill, without marginal setae; basis expanded, 0.80 × as wide and 2.60 × as long as coxa, width longest at proximal 1/3 and gradually diminished distally, anterior margin slightly convex, lined with simple setae, posterior margin lined with elongate setae; ischium 0.15 × as long as basis; merus anterodistally expanded, 0.31 × wider than long, 0.58 × as long as basis, anterodistal corner produced, apex blunt; carpus not expanded, 0.46 × as long as basis; propodus 0.49 × as long as basis, linear; dactylus 0.38 × as long as propodus, unguis developed.

Pereopod 4 (Fig. 2H, I ) similar to pereopod 3 except that merus 0.92 × as long as that of pereopod 3; different number or position of several setae.

Pereopod 5 (Fig. 3A ) coxa bilobate, anterior lobe larger than posterior lobe, expanded ventrally (1.00 × longer than wide), margin rounded, lined with seven simple setae; posterior lobe with two setae at posterior corner (ventral one very short); coxal gill present, subovate; oostegite present, narrow, shortest, without marginal setae; basis expanded, subrectangular, 0.55 × wider than long, anterior margin slightly convex, lined with three single robust setae and two pairs of robust and simple setae, with one cluster of elongate simple setae at distal corner, posterior margin lined with twelve elongate simple setae, distal corner produced forming an angle; merus posterodistally expanded, 0.42 × as wide and 0.80 × as long as basis, anterior margin with two clusters of simple setae marginally and one cluster of simple setae distally, posterior margin with one single robust seta and one pair of unequal setae marginally and one cluster of robust setae distally; carpus not expanded, 0.69 × as long as basis, anterior margin with two marginal clusters and one distal cluster of setae, posterior margin with one marginal and one distal clusters of setae; propodus linear, 1.03 × as long as carpus, anterior margin with three setal clusters (longest seta of distal cluster slightly exceeding end of propodus) and one pair of locking robust setae distally, posterior margin with one single and one pair of marginal short seta and one distal cluster of elongate setae; dactylus 0.31 × as long as propodus, unguis developed.

Pereopod 6 (Fig. 3B, C ) 1.14 × as long as pereopod 5; coxa bilobate, anterior lobe 0.62 × as long as that of pereopod 5, with one seta only on ventral margin, posterior lobe expanded backward, with one seta at posterior corner; coxal gill present, subovate; oostegite absent; basis expanded, subrectangular, 1.16 × as long and 1.00 × as wide as that of pereopod 5, 0.46 × wider than long, anterior margin slightly convex, lined with three single robust setae and three clusters of robust and simple setae, with one cluster of elongate simple setae at distal corner, posterior margin lined with twelve setae, distal corner produced forming an angle; merus posterodistally expanded, 1.22 × as long as that of pereopod 5, 0.50 × as wide and 0.84 × as long as basis, anterior margin with three marginal clusters and one distal cluster of simple setae, posterior margin with two marginal clusters and one distal cluster of simple and robust setae; carpus not expanded, 0.73 × as long as basis, anterior margin with three marginal clusters and one distal cluster of simple and robust setae, posterior margin with one simple seta and one cluster of simple and robust setae marginally and one cluster of setae distally; propodus linear, 0.92 × as long as carpus, anterior margin with three setal clusters (longest seta of distal cluster not exceeding end of propodus) and one pair of locking robust setae distally, posterior margin with one marginal short seta and one distal cluster of elongate setae; dactylus 0.37 × as long as propodus, unguis developed.

Pereopod 7 (Fig. 3D, E ) 1.06 × as long as pereopod 6; coxa unilobed, subtriangular, 0.77 × as long as that of pereopod 6, with one seta on ventral margin, posteriorly expanded with one seta at posterior corner;); coxal gill and oostegite absent; basis expanded, subrectangular, 1.00 × as long and 0.92 × as wide as that of pereopod 6, 0.42 × wider than long, anterior margin slightly convex, lined with three single setae and two clusters of setae, with one cluster of elongate simple setae at distal corner, posterior margin lined with eight setae, distal corner slightly produced but angle smaller than those of pereopods 6 and 7; merus posterodistally expanded, 0.80 × as long as that of pereopod 6, 0.54 × as wide and 0.67 × as long as basis, anterior margin with two marginal clusters and one distal cluster of simple setae, posterior margin with one single robust seta and one cluster of simple and robust setae marginally, and one cluster of simple and robust setae distally; carpus not expanded, rectangular, 0.24 × as wide as long, 1.09 × as long as merus, anterior margin with three marginal clusters and one distal cluster of simple and robust setae, posterior margin with one simple seta and one cluster of simple and robust setae marginally, and one cluster of simple and robust setae distally; propodus linear, 1.11 × as long as carpus, anterior margin with three setal clusters (longest seta of distal cluster not exceeding end of propodus) and one pair of locking robust setae distally, posterior margin with two marginal short setae and one distal cluster of setae posteriorly (shorter than those of pereopods 6 and 7); dactylus 0.38 × as long as propodus, unguis developed.

Sternal gills (Fig. 4A ) present in pereonites 2 to 5 (1+2+1+1 in formulae), narrower than oostegites, shortest in that of pereonite 5.

Epimeral plate 1 subquadrate, a little produced posteroventrally, ventral margin without setae, posterior margin with four setae, posterodistal corner slightly notched bearing one elongate seta. Epimeral plate 2 subquadrate, larger than plate 1, ventral margin with two submarginal setae anteriorly, posterior margin with three setae, posterodistal corner slightly notched bearing one elongate seta. Epimeral plate 3 posterior margin with three setae, posterodistal corner without notch, rounded, ventral margin with three submarginal setae anteriorly, posteriorly emarginated. (Fig. 3I ).

Pleopod 1 (Fig. 3F ) peduncle with one pair of retinaculae mediodistally and one cluster of three simple setae laterodistally; outer ramus 1.55 × as long as peduncle, composed of twelve articles; inner ramus 1.85 × as long as peduncle, composed of eleven articles (coalesced 1st article as long as proximal four articles of outer ramus combined).

Pleopod 2 (Fig. 3G ) peduncle 1.08 × as long as that of pleopod 1, with one pair of retinaculae mediodistally and one pair of simple setae laterodistally; outer ramus as long as peduncle, composed of nine articles; inner ramus as long as outer ramus, composed of seven articles (coalesced 1st article as long as proximal four articles of outer ramus combined).

Pleopod 3 (Fig. 3H ) 1.11 × as long as pleopod 2; peduncle 0.91 × as long as that of pleopod 2, with one pair of retinaculae mediodistally and one pair of simple setae laterodistally; outer ramus 1.36 × as long as peduncle, composed of ten articles; inner ramus 1.21 × as long as outer ramus, composed of ten articles (coalesced 1st article 1.20 × as long as proximal two articles of outer ramus combined).

Uropod 1 (Fig. 4C ) peduncle with one basofacial seta, with three marginal robust setae and one distal robust seta dorsolaterally, with one distal robust seta dorsomedially; outer ramus 0.59 × as long as peduncle, with one simple seta dorsomedially and two robust setae dorsolaterally, apical cluster composed of five robust setae; inner ramus 1.32 × as long as outer ramus, with three robust setae dorsomedially, apical cluster composed of five robust and two simple setae, with one elongate seta on ventral margin subproximally.

Uropod 2 (Fig. 4D ) 0.70 × as long as uropod 1; peduncle 0.62 × as long as that of uropod 1, with one marginal seta and one distal seta on both lateral and medial margins; outer ramus 0.77 × as long as peduncle, with two robust setae dorsolaterally, apical cluster composed of five robust setae; inner ramus 1.35 × as long as outer ramus, with three robust setae dorsomedially, apical cluster composed of one simple seta and six robust setae (apex of one robust seta abnormal).

Uropod 3 (Fig. 4E ) uniramous, 0.91 × as long as uropod 1; peduncle short, 0.58 × as long as that of uropod 2, with two minute setae on medial margin, with two setal clusters on mediodistal and laterodistal corners; ramus 3.1 × as long as peduncle, bi-articulate, proximal article gradually diminished in width, with three lateral and four medial clusters of setae (longest one of distal cluster exceeding distal article of ramus), distal article 0.13 × as long as proximal article, with three simple setae apically.

Telson (Fig. 4F ) 0.78 × as wide as long, cleft for 43% of length, each lobe with one cluster of two or three penicillate setae dorsally, and one penicillate seta and three robust setae on apex.

Remarks.

Pseudocrangonyx concavus sp. nov. resembles Pseudocrangonyx asiaticus sensu Uéno (1934), but differs in the absence of calceoli in the flagellum of antenna 1 (compared to the slender calceoli present in that of P. asiaticus ), in the presence of seven dentate setae on the apical margin of outer plate (compared to five in P. asiaticus ) and eight setae apically on the palp of maxilla 1 (compared to four in P. asiaticus ), by the more expanded basis of pereopods 5-7, by bearing sternal gills from pereonites 2 to 5 of 1+2+1+1 in formulae, by the presence of three and four setae on posterior margins of epimeral plates 2 and 3, respectively (compared to six and seven setae in P. asiaticus ), by the emarginated posteroventral margin of epimeral plate 3 (not emarginated in P. asiaticus ), by the presence of only one subproximal elongate seta on the ventral margin of the inner ramus on uropod 1 (compared to four in P. asiaticus ), and by the longer peduncle of uropod 2 than that of P. asiaticus ( Uéno 1934).

Figures

Figure 1. Pseudocrangonyx concavus sp. nov. Holotype: female, NIBRV 0000862807, 9.2 mm, from Hwansangul Cave, South Korea. A habitus B head C antenna 1 D, E antenna 2, lateral (D) and medial (E) F upper lip G lower lip H right mandible I incisor and lacinia mobilis of left mandible J maxilla 1 K maxilla 2 L maxilliped.

Figure 2. Pseudocrangonyx concavus sp. nov. Holotype: female, NIBRV 0000862807, 9.2 mm, from Hwansangul Cave, South Korea. A gnathopod 1 B rastellate seta of gnathopod 1 C palm of gnathopod 1 D gnathopod 2 E rastellate setae of gnathopod 2 F palm of gnathopod 2 G pereopod 3 H pereopod 4 I oostergite of pereopod 4.

Figure 3. Pseudocrangonyx concavus sp. nov. Holotype: female, NIBRV 0000862807, 9.2 mm, from Hwansangul Cave, South Korea. A pereopod 5 B pereopod 6 C coxal gill of pereopod 6 D pereopod 7 E coxa of pereopod F pleopod 1 G pleopod 2 H pleopod 3 I epimeral plates 1 - 3. Abbreviation: Ep, epimeral plate.

Figure 4. Pseudocrangonyx concavus sp. nov. Holotype: female, NIBRV 0000862807, 9.2 mm, from Hwansangul Cave, South Korea. A sternal gills B pleonites and urosomites, dorsal C uropod 1 D uropod 2 E uropod 3 F telson. Abbreviations: Pl, pleonite; Uro, urosomite; sg, sternal gill; ir, inner ramus; and or, outer ramus.