Pseudocrangonyx gracilipes, 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 gracilipes sp. nov. Figs 5 , 6 , 7 , 8

Korean name.

Ga-neun-da-ri-dong-gul-yeop-sae-u, new

Type locality.

Gosugul Cave, Danyang-gun, Chungcheongbuk-do, South Korea; 36°59'12"N, 128°22'52"E.

Material examined. Type material. Holotype: 1 female, 9.9 mm, NIBRIV0000862808, 19 Jan 2001. Paratype: 1 male, 1.4 mm, NIBRIV0000872410, 11 Nov 1973; 1 male and 1 female, NIBRIV0000872411, 27 Sep 1975. All type materials were collected by YG Choi.

Etymology.

The specific name originates from the combination of the Latin word gracilis, meaning slender, thin and pes, meaning foot. This name refers to the shape of the elongate pereopods that are more evident than those of other pseudocrangonyctids.

Diagnosis.

Maxilla 1 inner lobe with four plumose setae on apical margin; 2nd palp article apex with six robust setae (weakly dentate). Maxilla 2 inner lobe with one oblique row of four plumose setae on surface; outer lobe apical margin without plumose setae. Maxilliped inner lobe with three dentate robust setae on apex. Gnathopod 1 carpus 0.55 × as long as basis, with one pair of robust setae marginally on anterior margin, carpal lobe with three rastellate setae. Gnathopod 2 as long as gnathopod 1, carpal lobe with one cluster of three rastellate setae subdistally. Pereopods 5-7 articles slightly slender and elongate. Sternal gills present from pereonites 2-5 (1+1+1+1 in formulae). Epimeral plate 2 ventral margin with four submarginal setae anteriorly, posterodistal corner slightly notched bearing one elongate seta. Epimeral plate 3 posterior margin with eight setae, posterodistal corner produced backward, with weak notch, bearing one elongate seta, ventral margin with five submarginal setae anteriorly, not concave. Pleopods 1-3 peduncles with robust setae laterally. Uropod 1 inner ramus with two elongate setae subproximally on ventral margin. Telson 0.63 × as wide as long, cleft for 47% of length.

Description.

Holotype female: Body (Fig. 5A ) approximately 9.9 mm long.

Head (Fig. 5B ) 0.76 × as long as pereonite 1; rostrum reduced, with minute setae; lateral cephalic lobe anteriorly expanded, apex rounded, slightly dilated anteroventrally; antennal sinus not deep; eye absent.

Antenna 1 (Fig. 5C ) 0.53 × as long as body; 1st-3rd peduncular articles length ratio of 1.00: 0.86: 0.48; 1st article stout, with two pairs of robust setae on posterior margin; accessory flagellum bi-articulate, last article very reduced, with one cluster of simple setae distally; flagellum 1.45 × as long as peduncles, composed of 22 articles, calceoli absent, aesthetascs present from 16th-20th and last articles.

Antenna 2 (Fig. 5D ) 0.51 × as long as antenna 1; antennal cone developed, apex rounded; 4th peduncular article 0.97 × as long as 2nd peduncular article of antenna 1, margins parallel, 0.25 × wider than long, densely setose with several rows or clusters of various setae; 5th article 1.00 × as long and 0.67 × as wide as 4th article, two calceoli present on medial surface, also densely setose with several rows or clusters of various setae; flagellum composed of seven articles, 0.91 × as long as 5th peduncular article, single calceoli present from 1st-4th articles medially, aesthetascs absent.

Upper lip (Fig. 5E ) anteriorly rounded, apex covered with minute setae, not notched.

Lower lip (Fig. 5F ) inner lobes indistinct; outer lobes covered with minute setae; mandibular processes developed.

Mandible (Fig. 5G-I ) incisor 5-dentate on right side and 4-dentate on left side; lacinia mobilis tri-cuspidate (two finely dentate and one not dentate) on right side and bi-furcate (one 4-dentate and the other not dentate) on left side; six raker setae present on both sides; molar process columnar, triturative, with one plumose seta on right side only; palp tri-articulate; 2nd article convex and with 15 setae medially; 3rd article subfalcate, 1.16 × as long as 2nd article, lined with 27 setae from medial margin to apex..

Maxilla 1 (Fig. 5J ) inner lobe subrhomboid, with four plumose setae on apical margin; outer lobe with seven dentate robust setae; palp bi-articulate, 2nd article apex obviously exceeding apical setae of outer plate, with six robust setae (weakly dentate) along distomedial to apical margins, with one oblique row of six setae subdistally.

Maxilla 2 (Fig. 5K ) inner lobe slightly shorter but wider than outer lobe, with one oblique row of four plumose setae on surface and two rows of simple setae on apical margin; outer lobe apical margin also with two rows of simple setae (without plumose setae).

Maxilliped (Fig. 6A ) inner lobe subrectangular with three dentate robust setae on apex and eleven plumose setae mediodistally and subapically; outer lobe elongate semicircular, 0.62 × as long as 2nd palp article, lined with four dentate robust setae (one distal seta smallest) and four plumose setae apically; palp composed of four articles; 2nd article with many setae on medial margin; 3rd article slightly dilated distally, 0.56 × as long as 2nd article; 4th article falcate, 0.61 × as long as 3rd article, apical setae 0.76 × as long as 4th article.

Gnathopod 1 (Fig. 6B, C ) coxa subrectangular, 1.52 × wider than long, anteroventral corner slightly produced with nine setae marginally, ventral margin a little concaved, with one seta posteriorly, posterior margin humped proximally; basis obtuse trapezoidal, posteriorly expanded, 0.45 × wider than long, lined with elongate simple setae posteriorly, anterior margin obliquely truncated distally, without setae; ischium 0.27 × as long as basis, with small anterior lobe; carpus 0.55 × as long as basis, with one pair of robust setae marginally and one cluster of simple setae on anterior margin, carpal lobe not developed, apex rounded with three rastellate setae and many simple or serrate setae; propodus subtriangular, 1.38 × as long and 1.64 × as wide as basis, with six robust setae laterally along posterior margin (successively increasing distally), palm irregular, finely serrated, lined with nine robust setae medially, defined by largest lateral seta of posterior margin; dactylus exceeding largest lateral seta of posterior margin, inner margin toothed, outer margin with four setae, unguis developed.

Gnathopod 2 (Fig. 6D-F ) as long as gnathopod 1; coxa 1.37 × as long as that of gnathopod 1, 1.14 × wider than long, anterior and ventral margins not produced, rounded, lined with eleven setae, ventral margin with three setae posteriorly, posterior margin humped proximally; coxal gill present, subovate; oostegite present, narrow, shorter than that of coxal gill, without marginal setae; basis subtrapezoidal, posteriorly expanded, 0.33 × wider than long, lined with elongate simple setae posteriorly, anterior margin with two setae subdistally; ischium 0.21 × as long as basis, with small anterior lobe; carpus 0.63 × as long as basis, with two robust setae on anterior margin, carpal lobe not developed, broad, with seven clusters of many simple or serrate setae, with one cluster of three rastellate setae subdistally; propodus trapezoidal, 0.93 × as long and 1.41 × as wide as basis, anterior margin slightly convex, posterior margin 0.48 × as long as anterior margin, lined with six clusters of elongate setae, palm irregular, finely serrated, lined with nine medial and eleven lateral robust setae (palm defined by two unequal setae distally among lateral setae); dactylus exceeding palm, inner margin toothed, outer margin with three setae, unguis developed.

Pereopod 3 (Fig. 7A, B ) coxa subrectangular, 1.27 × wider than long, anteriorly convex, with ten setae anteriorly, ventral margin a little concave, with four setae posteriorly; coxal gill present, subovate; oostegite present, narrow, shorter than that of coxal gill, without marginal setae; basis expanded, 0.70 × as wide and 2.55 × as long as coxa, width longest at proximal 1/3 and slightly diminished distally, anterior margin lined with simple setae, posterior margin lined with elongate setae; ischium 0.16 × as long as basis; merus anterodistally expanded, 0.30 × wider than long, 0.60 × as long as basis, anterodistal corner produced, apex blunt; carpus not expanded, 0.48 × as long as basis; propodus linear, 0.93 × as long as carpus; dactylus 0.44 × as long as propodus, unguis developed.

Pereopod 4 (Fig. 7C ) similar to pereopod 3 except that carpus and propodus 1.11 × as long as those of pereopod 3; different number or position of several setae.

Pereopod 5 (Fig. 7D ) coxa bilobate, anterior lobe larger than posterior lobe, expanded ventrally (1.14 × longer than wide), margin rounded, lined with 13 simple setae; posterior lobe with two setae at posterior corner (ventral one short); coxal gill present, subovate; oostegite present, narrow, shorter than that of coxal gill, length shortest, without marginal setae; basis expanded, subrectangular, 0.46 × wider than long, anterior margin slightly convex, lined with five single robust setae and one pair of robust setae, posterior margin lined with 18 simple setae, distal corner produced and forming angle; merus posterodistally expanded, 0.40 × as wide and 0.86 × as long as basis, anterior margin with one simple seta and three clusters of simple setae marginally, and one cluster of setae distally, posterior margin with five single robust setae marginally, and one cluster of robust and simple setae distally; carpus not expanded 1.00 × as long as basis, anterior and posterior margins with three marginal clusters and one distal cluster of setae, respectively; propodus linear, 1.11 × as long as carpus, anterior margin with six setal clusters (longest seta of distal cluster not exceeding end of propodus) and one pair of locking robust setae distally, posterior margin with five pairs of short setae marginally and one cluster of elongate setae distally; dactylus slender, 0.32 × as long as propodus, unguis developed.

Pereopod 6 (Fig. 7E, F ) 1.12 × as long as pereopod 5; coxa bilobate, anterior lobe 0.60 × as long as that of pereopod 5, with four setae on ventral margin, posterior lobe expanded backward, with two setae at posterior corner (ventral one very short); coxal gill present, subovate; oostegite absent; basis expanded, subrectangular, 1.13 × as long and 1.08 × as wide as that of pereopod 5, 0.46 × wider than long, anterior margin slightly convex, lined with three single robust setae and two clusters of robust setae, with one cluster of robust setae at distal corner, posterior margin lined with 14 setae, posterodistal corner produced forming an angle; merus posterodistally expanded, 1.24 × as long as that of pereopod 5, 0.44 × as wide and 0.95 × as long as basis, anterior and posterior margins with four single setae or clusters of setae marginally and one cluster of setae distally, respectively; carpus not expanded, 0.73 × as long as basis, anterior margin with four clusters of setae marginally and one cluster of setae distally, posterior margin with one simple seta and three clusters of simple and robust setae marginally, and one cluster of setae distally; propodus linear, 0.88 × as long as carpus, anterior margin with one robust seta and four clusters of setae marginally (longest seta of distal cluster not exceeding end of propodus) and one pair of locking robust setae distally, posterior margin with four pairs of short setae marginally and one cluster of elongate setae distally; dactylus 0.39 × as long as propodus, unguis developed.

Pereopod 7 (Fig. 7G ) 0.97 × as long as pereopod 6; coxa unilobed, subtriangular, 0.73 × as long as that of pereopod 6, with one seta on ventral margin, posteriorly expanded with four setae at posterior corner; coxal and oostegite absent; basis expanded, subrectangular, 1.01 × as long and 0.87 × as wide as that of pereopod 6, 0.39 × wider than long, anterior margin slightly convex, lined with six robust setae, with one cluster of setae at distal corner, posterior margin lined with eleven setae, distal corner slightly produced but angle smaller than in pereopods 6 and 7; merus posterodistally expanded, 0.82 × as long as that of pereopod 6, 0.57 × as wide and 0.77 × as long as basis, anterior margin with four marginal clusters and one distal cluster of setae, posterior margin with one single robust seta and three clusters of simple and robust setae marginally, and one cluster of simple and robust setae distally; carpus not expanded, rectangular, 1.11 × as long as merus, anterior margin with four clusters of setae marginally and one cluster of setae distally, posterior margin with two clusters of setae marginally and one cluster of setae distally; propodus linear, 1.22 × as long as carpus, anterior margin with five clusters of setae (without elongate setae) and one pair of locking robust setae distally; posterior margin with three pairs of short setae marginally and one cluster of setae distally (shorter than those of pereopods 6 and 7); dactylus 0.36 × as long as propodus, unguis developed.

Sternal gills (Fig. 8B ) present from pereonites 2-5 (1+1+1+1 in formulae), narrower than oostegites, shortest in that of pereonite 5.

Epimeral plate 1 subquadrate, slightly produced posteroventrally, ventral margin without setae, posterior margin with six setae, posterodistal corner slightly notched bearing one elongate seta. Epimeral plate 2 subquadrate, larger than epimeron 1, ventral margin with four submarginal setae anteriorly, posterior margin with seven setae, posterodistal corner slightly notched bearing one elongate setae. Epimeral plate 3 posterior margin with eight setae, posterodistal corner produced backward, with weak notch, bearing one elongate seta, ventral margin with five submarginal setae anteriorly, not emarginated (Fig. 8A ).

Pleopod 1 (Fig. 8C ) peduncle with one pair of retinaculae mediodistally and one pair of simple setae laterodistally, with two robust setae laterally; outer ramus 1.55 × as long as peduncle, composed of 13 articles; inner ramus 1.75 × as long as peduncle, composed of eleven articles (coalesced 1st article as long as proximal three articles of outer ramus combined).

Pleopod 2 (Fig. 8D ) peduncle 1.11 × as long as that of pleopod 1, with one pair of retinaculae mediodistally and one pair of simple setae laterodistally, with one robust seta laterally; outer ramus 1.42 × as long as peduncle, composed of 13 articles; inner ramus 1.48 × as long as peduncle, composed of eleven articles (coalesced 1st article 0.90 × as long as proximal three articles of outer ramus combined).

Pleopod 3 (Fig. 8E ) 0.91 × as long as pleopod 2; peduncle 0.92 × as long as that of pleopod 2, with one pair of retinaculae mediodistally and one pair of simple setae laterodistally, with one robust seta laterally; outer ramus 1.20 × as long as peduncle, composed of eleven articles, 1st article not fully coalesced and with trace; inner ramus 1.46 × as long as outer ramus, composed of ten articles, 1st article not fully coalesced and with trace, 9th and 10th articles coalesced.

Uropod 1 (Fig. 8F ) peduncle with one basofacial seta, with four marginal setae and one distal seta dorsolaterally, with two marginal setae and one distal seta dorsomedially; outer ramus 0.63 × as long as peduncle, with one robust seta dorsomedially and two robust setae dorsolaterally, apical cluster composed of five robust setae; inner ramus 1.15 × as long as outer ramus, with one robust seta dorsolaterally and four robust setae dorsomedially, apical cluster composed of five robust setae and one simple and one penicillate seta, with two elongate setae subproximally on ventral margin.

Uropod 2 (Fig. 8G ) 0.59 × as long as uropod 1; peduncle 0.52 × as long as that of uropod 1, with three marginal setae and one distal seta dorsolaterally, with one marginal seta and one distal seta dorsomedially; outer ramus 0.84 × as long as peduncle, with two robust setae dorsolaterally, apical cluster composed of five robust setae; inner ramus 1.50 × as long as outer ramus, with two robust setae dorsolaterally and three robust setae dorsomedially, apical cluster composed of seven robust setae and one penicillate seta.

Uropod 3 (Fig. 8H ) uniramous, 0.83 × as long as uropod 1; peduncle short, 0.55 × as long as uropod 2, with two minute setae on medial margin, with one dorsal and one ventral cluster of robust setae laterodistally; ramus 4.17 × as long as peduncle, bi-articulate, proximal article gradually diminished distally, with five lateral and five medial clusters of setae (longest seta of each distal cluster exceeding end of last article), distal article 0.13 × as long as proximal article, with five simple setae apically.

Telson (Fig. 8I ) 0.63 × as wide as long, cleft for 47% of length, each lobe with one pair of penicillate setae dorsally, and one penicillate seta and two robust setae on apex.

Remarks.

Pseudocrangonyx gracilipes sp. nov. resembles with its several congeners including P. bohaensis (Derzhavin, 1927), P. yezonis Akatsuka & Komai, 1992, P. relicta Labay, 1999, and P. camtschaticus Birstein, 1955 in having the notched posterodistal corners of epimeral plates 2 and 3. However, this new species is distinguished from these species by the more produced posterodistal corner of epimeral plate 3 ( Birstein 1955, Akatsuka and Komai 1922, Labay 1999).

This character state of the epimeral plates is also observed in P. villosus sp. nov., but P. gracilipes sp. nov. has four plumose setae on the inner plate of maxilla 1 (compared to seven in P. villosus sp. nov.), four plumose setae on inner plate of maxilla 2 (compared to ten in P. villosus sp. nov.), both three rastellate setae on gnathopods 1 and 2 (compared to two rastellate setae in P. villosus sp. nov.), and the presence of the more slender and elongated pereopods 5-7.

Figures

Figure 5. Pseudocrangonyx gracilipes sp. nov. Holotype: female, NIBRV 0000862808, 9.9 mm, from Gosugul Cave, South Korea. A habitus B head C antenna 1 D antenna 2 E upper lip F lower lip G, H right mandible I left mandible J maxilla 1 K maxilla 2.

Figure 6. Pseudocrangonyx gracilipes sp. nov. Holotype: female, NIBRV 0000862808, 9.9 mm, from Gosugul Cave, South Korea. A maxilliped B gnathopod 1 C rastellate setae and palm of gnathopod 1 D gnathopod 2 E rastellate setae of gnathopod 2 F palm of gnathopod 2.

Figure 7. Pseudocrangonyx gracilipes sp. nov. Holotype: female, NIBRV 0000862808, 9.9 mm, from Gosugul Cave, South Korea. A pereopod 3 B coxal gill of pereopod 3 C pereopod 4 D pereopod 5 E pereopod 6 F coxal gill of pereopod 6 G pereopod 7.

Figure 8. Pseudocrangonyx gracilipes sp. nov. Holotype: female, NIBRV 0000862808, 9.9 mm, from Gosugul Cave, South Korea. A epimeral plates 1 - 3 B sternal gills C pleopod 1 D pleopod 2 E pleopod 3 F uropod 1 G uropod 2 H uropod 3 I telson. Abbreviations: Ep, epimeral plate; Pn, pereonite; sg, sternal gill; ir, inner ramus; and or, outer ramus.