Pseudocrangonyx crassus, 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 crassus sp. nov. Figs 9 , 10 , 11 , 12

Korean name.

Keun-deo-deum-i-dong-gul-yeop-sae-u, new

Type locality.

Gossigul Cave, Yeongwol-gun, Gangwon-do, South Korea; 37°08'00"N, 128°31'21"E.

Material examined. Type material. Holotype: 1 male, 10.6 mm, NIBRIV0000862809, collected from the type locality on 19 Jan 2001 by YG Choi.

Etymology.

The specific name originates from the Latin word crassus meaning thick. This name refers to the shape of the 4th and 5th articles of antenna 2.

Diagnosis.

Antenna 2, 4th and 5th peduncular articles expanded, plump medially, calceoli and aesthetascs absent. Maxilla 1 inner lobe with five plumose setae on apical margin; 2nd palp article with six robust setae along distomedial to apical margins. Maxilla 2 inner lobe with one oblique row of five plumose setae on surface; outer lobe without plumose setae. Gnathopods 1 and 2 each possessing carpus with three rastellate setae, respectively. Pereopods 3 and 4 basis bearing elongate setae on posterior margins. Sternal gills present on pereonites 2, 3, and 5 (1+1+0+1 in formulae). Epimeral plate 3 posteroventral corner slightly produced. Telson cleft for 39% of length.

Description.

Holotype male: Body (Fig. 9A ) approximately 10.6 mm long.

Head (Fig. 9B ) 1.30 × as long as pereonite 1; rostrum reduced, with one minute seta; lateral cephalic lobe anteriorly expanded, apex rounded, slightly dilated anteroventrally; antennal sinus not deep; eye absent.

Antenna 1 (Fig. 9C ) 0.50 × as long as body; 1st-3rd peduncular articles length ratio of 1.00: 0.80: 0.56; 1st article stouter than 2nd and 3rd articles, without robust setae on posterior margin; accessory flagellum bi-articulate, last article very reduced; flagellum 1.28 × as long as peduncles, composed of 18 articles, calceoli absent, aesthetascs present from proximal 3rd to last articles.

Antenna 2 (Fig. 9D ) 0.62 × as long as antenna 1; antennal cone developed, apex rounded; 4th and 5th peduncular articles expanded, plump medially; 4th article 0.93 × as long as 1st peduncular article of antenna 1, anterior margin convex, with three clusters of robust setae, posterior margin distally expanded, rounded posterodistally; 5th article expanded at the middle, 0.98 × as long and 0.69 × as wide as 4th article, calceoli absent; flagellum composed of six articles, 0.77 × as long as 5th peduncular article; calceoli and aesthetascs absent.

Upper lip (Fig. 9E ) anteriorly rounded, apex covered with minute setae, not notched.

Lower lip (Fig. 9F ) inner lobes indistinct; outer lobes covered with minute setae; mandibular processes developed.

Mandible (Fig. 9G, H ) incisor 5-dentate on both sides; lacinia mobilis tri-cuspidate (two finely dentate and one not dentate) on right and bi-furcate (one 4-dentate and the other not dentate) on left side; seven and eight raker setae present on right and left sides; molar process columnar, triturative, with one plumose seta on right side only; palp tri-articulate; 2nd article convex and with 14 setae medially; 3rd article subfalcate, 1.2 × as long as 2nd article, medial margin lined with 23 setae from medial margin to apex.

Maxilla 1 (Fig. 9I ) 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 six robust setae along distomedial to apical margins, with one oblique row of five setae subdistally.

Maxilla 2 (Fig. 9J ) inner lobe slightly shorter but wider than outer lobe, with one oblique row of five 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. 10A ) inner lobe subrectangular, with eight dentate robust setae on apex and eight plumose setae mediodistally and subapically; outer lobe elongate semicircular, 0.70 × as long as 2nd palp article, with five dentate robust setae and seven weakly plumose setae apically; palp composed of four articles; 2nd article with many setae on medial margin; 3rd article slightly dilated distally, 0.70 × as long as 2nd article; 4th article falcate, 0.49 × as long as 3rd article, apical setae 0.76 × as long as 4th article.

Gnathopod 1 (Fig. 10B-D ) coxa subrectangular, 1.63 × wider than long, anteroventral corner not produced, rounded, with seven setae marginally, ventral margin slightly concave, with three setae posteriorly, posterior margin humped proximally; basis obtuse trapezoidal, posteriorly expanded, 0.49 × wider than long, lined with elongate simple setae posteriorly, anterior margin without setae; ischium 0.28 × as long as basis, with small anterior lobe; carpus 0.62 × as long as basis, with one single seta and one pair of robust setae on anterior margin, carpal lobe not developed, apex rounded with three rastellate setae and many simple or serrate setae; propodus subovate, 1.24 × as long and 1.39 × as wide as basis, posterior margin short, 0.24 × as long as anterior margin, with four robust setae laterally along posterior margin distally and nine 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, apex reaching largest lateral seta of posterior margin, inner margin toothed, outer margin with four setae, unguis developed.

Gnathopod 2 (Fig. 10E-H ) 1.07 × as long as gnathopod 1; coxa 1.29 × as long as that of gnathopod 1, 1.29 × wider than long, anterior and ventral margins not produced, rounded, lined with eight setae, ventral margin with four setae posteriorly, posterior margin humped proximally; coxal gill present, subovate; basis subtrapezoidal, posteriorly expanded, 0.92 × as wide as that of gnathopod 1, 0.36 × wider than long, lined with elongate simple setae posteriorly, anterior margin with two setae subdistally; ischium 0.23 × as long as basis, with small anterior lobe; carpus 0.60 × as long as basis, with two pairs of robust setae on anterior margin, carpal lobe not developed, broad, with seven clusters of many simple or serrate setae, with three rastellate setae distally; propodus trapezoidal, 0.93 × as long and 1.31 × as wide as basis, anterior margin slightly convex, posterior margin 0.52 × as long as anterior margin, lined with six clusters of elongate setae, palm irregular, finely serrated, lined with six medial and nine 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. 11A ) coxa rectangular, 1.35 × wider than long, with ten setae anteriorly and three setae posteroventrally, ventral margin a little concave; coxal gill present, subovate; basis expanded, 0.78 × as wide and 2.65 × as long as coxa, width longest at proximal 1/3 and slightly diminished distally, anterior margin slightly convex, lined with nine simple setae, posterior margin lined with 18 elongate setae; ischium 0.16 × as long as basis; merus anterodistally expanded, 0.36 × wider than long, 0.51 × as long as basis, anterodistal corner produced, apex blunt; carpus not expanded, 1.00 × as long as merus; propodus linear, 1.06 × as long as carpus; dactylus 0.43 × as long as propodus, unguis developed.

Pereopod 4 (Fig. 11B, C ) each article similar to but slightly shorter than those of pereopod 3, except for the number and positions of several setae.

Pereopod 5 (Fig. 11D, E ) coxa with additional tumid lobe proximally, bilobate, anterior lobe larger than posterior lobe, expanded ventrally (1.09 × longer than wide), margin rounded, lined with twelve simple setae; posterior lobe with two setae at posterior corner (ventral one very short); coxal gill present, subovate; basis expanded, subrectangular, 0.52 × wider than long, anterior margin slightly convex, lined with five single robust setae and two clusters of robust setae, with one cluster of elongate setae at distal corner, posterior margin lined with 21 simple setae, with two submarginal robust setae proximally, distal corner produced forming an angle; merus posterodistally expanded, 0.38 × as wide and 0.78 × as long as basis, anterior margin with three clusters of setae marginally and one cluster of setae distally, posterior margin with one single robust seta and two clusters of setae marginally, and one cluster of setae distally; carpus not expanded, 0.92 × as long as merus, anterior margin with two clusters of setae and one single seta marginally, and one cluster of setae distally, posterior margin with three clusters bearing elongate simple setae marginally and one cluster of setae distally; propodus linear, 1.17 × as long as carpus, anterior margin with six setal clusters (all clusters with elongate setae and those of distal cluster exceeding end of propodus) and one pair of locking robust setae distally, posterior margin with three marginal clusters of short setae and one cluster of elongate setae distally; dactylus slender, 0.29 × as long as propodus, unguis developed.

Pereopod 6 (Fig. 11F, G ) 1.21 × as long as pereopod 5; coxa with additional tumid lobe proximally, bilobate, anterior lobe 0.80 × as long as that of pereopod 5, with five robust setae on ventral margin, posterior lobe expanded backward, with two setae at posterior corner (ventral one short); coxal gill present, subovate; basis expanded, subrectangular, 1.12 × as long and 1.02 × as wide as that of pereopod 5, 0.47 × wider than long, anterior margin slightly convex, lined with more than four single robust setae and one clusters of robust setae, with one cluster of setae at distal corner, posterior margin lined with 14 setae, distal corner produced forming an angle; merus posterodistally expanded, 1.28 × as long as that of pereopod 5, 0.41 × as wide and 0.89 × as long as basis, anterior margin with four clusters of setae marginally and one cluster of setae distally, posterior margin with three clusters of setae marginally and one cluster of setae distally; carpus not expanded, 0.85 × as long as basis, anterior margin with three clusters of setae marginally and one cluster of simple and robust setae distally, posterior margin with one simple seta and three clusters of simple or robust setae marginally, and one cluster of setae distally; propodus linear, 1.08 × as long as carpus, anterior margin with one single seta and four clusters of setae marginally (longest seta of distal cluster exceeding end of propodus) and one pair of locking robust setae distally, posterior margin with one single seta, four pairs of short setae marginally and one distal cluster of elongate setae distally; dactylus 0.28 × as long as propodus, unguis developed.

Pereopod 7 (Fig. 11H ) 0.98 × as long as pereopod 6; coxa unilobed, subtriangular, 0.65 × as long as that of pereopod 6, with one seta on ventral margin, posteriorly expanded with three setae at posterior corner; basis expanded, subrectangular, 1.17 × as long and 0.92 × as wide as that of pereopod 6, 0.41 × wider than long, anterior margin slightly convex, lined with three single robust setae and two clusters of robust setae, with one cluster of setae at distal corner, posterior margin lined with ten setae, distal corner slightly produced but angle smaller than those of pereopods 6 and 7; merus posterodistally expanded, 0.82 × as long as that of pereopod 6, 0.55 × as wide and 0.68 × as long as basis, anterior margin with two clusters of setae marginally and one cluster of setae distally, posterior margin with one single seta and two clusters of setae marginally and one cluster of setae distally; carpus not expanded, rectangular, 0.22 × as wide as long, 1.13 × as long as merus, anterior margin with two marginal clusters and one distal cluster of simple and robust setae, posterior margin with two clusters of setae marginally and one cluster of simple and robust setae distally; propodus linear, 1.10 × as long as carpus, anterior margin with four setal clusters (without elongate setae) marginally and one pair of locking robust setae distally, posterior margin with one single seta and two pairs of short setae marginally, and one cluster of setae distally (shorter than those of pereopods 6 and 7), dactylus 0.29 × as long as propodus, unguis developed.

Sternal gills (Fig. 12A ) present on pereonites 2, 3, and 5 (1+1+0+1 in formulae), narrow, not short in pereonite 5.

Epimeral plate 1 subquadrate, slightly produced posteroventrally, ventral margin without setae, posterior margin with seven setae, posterodistal corner slightly notched bearing one elongate seta. Epimeral plate 2 subquadrate, larger than epimeron 1, ventral margin with two submarginal setae anteriorly, posterior margin with nine setae, posterodistal corner slightly notched bearing one elongate seta. Epimeral plate 3 posterior margin with six setae, posterodistal corner a little produced and without notch, ventral margin with four submarginal setae anteriorly, not emarginated (Fig. 12B ).

Pleopod 1 (Fig. 12C ) peduncle with one pair of retinaculae mediodistally and three simple setae laterodistally, with two robust setae laterally; outer ramus 1.40 × as long as peduncle, composed of twelve articles, 11th and 12th articles coalesced; inner ramus 1.54 × as long as peduncle, composed of ten articles (1st coalesced article exceeding three proximal articles of outer ramus combined).

Pleopod 2 (Fig. 12D ) peduncle 1.06 × as long as that of pleopod 1, with one pair of retinaculae mediodistally and one cluster of three simple setae laterodistally, with one robust seta laterally; outer ramus 1.43 × as long as peduncle, composed of 13 articles; inner ramus 0.92 × as long as outer ramus, composed of eight articles (1st coalesced article exceeding two proximal articles of outer ramus combined, last articles coalesced).

Pleopod 3 (Fig. 12E ) 0.78 × as long as pleopod 2; peduncle 0.95 × as long as that of pleopod 2, with one pair of retinaculae mediodistally and one pair of simple setae laterodistally, with one pair of setae laterally; outer ramus 1.00 × as long as peduncle, composed of nine articles, 1st article not fully coalesced and with trace; inner ramus 1.06 × as long as outer ramus, composed of seven articles, 1st article not fully coalesced and with trace, 5th article coalesced.

Uropod 1 (Fig. 12F ) peduncle with one basofacial seta, with five marginal setae and one distal seta dorsolaterally, with one marginal seta and one distal seta dorsomedially; outer ramus 0.60 × as long as peduncle, with two robust setae dorsolaterally, apical cluster composed of five robust setae; inner ramus 1.31 × as long as outer ramus, with one robust seta dorsolaterally and three robust setae dorsomedially, apical cluster composed of seven robust setae and one penicillate seta, with four elongate setae on ventral margin subproximally.

Uropod 2 (Fig. 12G ) 0.63 × as long as uropod 1; peduncle 0.55 × as long as that of uropod 1, with two marginal setae and one distal seta dorsolaterally, with one distal seta and one marginal seta dorsomedially; outer ramus 0.76 × as long as peduncle, with one robust seta dorsolaterally, apical cluster composed of five robust setae (one of them with abnormal apex); inner ramus 1.52 × as long as outer ramus, with two robust setae (bearing abnormal apices) dorsolaterally and two robust setae dorsomedially, apical cluster composed of seven robust setae (three of them with abnormal apices) and one penicillate seta.

Uropod 3 (Fig. 12H ) uniramous, 0.85 × as long as uropod 1; peduncle short, 0.61 × as long as uropod 2, distal margin with one dorsal and one medial clusters of robust setae; ramus 3.25 × as long as peduncle, bi-articulate, proximal article gradually diminished in width, with five lateral and five medial clusters of setae (longest seta of each distal cluster exceeding end of last article), distal article 0.16 × as long as proximal article, with six simple setae apically.

Telson (Fig. 12I ) 0.73 × as wide as long, cleft for 39% of length, each lobe with one pair of penicillate setae dorsally, and one penicillate seta and two robust setae on apex.

Remarks.

Pseudocrangonyx crassus sp. nov. is very similar to P. tiunovi Sidorov & Gontcharov, 2013 in having expanded peduncular articles and a reduced flagellum of antenna 2, in addition to bearing similarities in the general shape and length ratio of the articles in the gnathopods and pereopods. However, this new species differs from P. tiunovi by possessing more expanded 4th and 5th peduncular articles of antenna 2, longer palp articles of maxilla 1 bearing more robust setae (six in P. crassus sp. nov. compared to four in P. tiunovi ), a longer 3rd palp article on the maxilliped compared to P. tiunovi , three rastellate setae in both gnathopods 1 and 2 (one and two on gnathopods 1 and 2, respectively, in P. tiunovi ), more elongate setae on the basis posterior margins on pereopods 3 and 4, a more expanded anterior lobe of coxa 5, a slightly produced posteroventral corner of epimeral plate 3 (more produced in P. tiunovi ), and a telson cleft for 39% of length (cleft for 20% of length in P. tiunovi ) ( Sidorov and Gontcharov 2013).

Figures

Figure 9. Pseudocrangonyx crassus sp. nov. Holotype: male, NIBRV 0000862809, 10.6 mm, from Gosugul Cave, South Korea. A habitus B head C antenna 1 D antenna 2 E upper lip F lower lip G right mandible H left mandible I maxilla 1 J maxilla 2.

Figure 10. Pseudocrangonyx crassus sp. nov. Holotype: male, NIBRV 0000862809, 10.6 mm, from Gossigul Cave, South Korea. A maxilliped B gnathopod 1 C rastellate setae gnathopod 1 D and palm of gnathopod 1 E gnathopod 2 F rastellate setae of gnathopod 2 G palm of gnathopod 2 H coxal gill of gnathopod 2.

Figure 11. Pseudocrangonyx crassus sp. nov. Holotype: male, NIBRV 0000862809, 10.6 mm, from Gossigul Cave, South Korea. A pereopod 3 B pereopod 4 C coxal gill of pereopod 4 D pereopod 5 E coxa of pereopod 5 F pereopod 6 G coxal gill of pereopod 7 H pereopod 7.

Figure 12. Pseudocrangonyx crassus sp. nov. Holotype: male, NIBRV 0000862809, 10.6 mm, from Gossigul Cave, South Korea. A sternal gills B epimeral plates 1 - 3 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.