Pseudocrangonyx minutus, 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 minutus sp. nov. Figs 13 , 14 , 15 , 16

Korean name.

Jak-eun-dong-gul-yeop-sae-u, new

Type locality.

Gageodo-ri, Heuksan-myeon, Sinan-gun, Jeollanam-do, South Korea; 34°03'52.2"N, 125°06'55.7"E; an old tube well for using groundwater.

Material examined. Type material. Holotype: 1 adult female, 9.1 mm, NIBRIV0000862810. Paratypes: 2 males and 2 females, NIBRIV0000872412. All type materials collected on 7 Oct 2009 by Dr. M-S Kim.

Etymology.

The specific name originates from the Latin word minutus meaning small, petty. This name refers to more reduced pleopod articles compare to other pseudocrangonyctids.

Diagnosis.

Antenna 1, 0.33 × as long as body; flagellum composed of 15 articles. Antenna 2 flagellum composed of seven articles. Both mandibles bearing five raker setae. Maxilla 1 inner lobe with four plumose setae on apical margin; 2nd palp article with six robust setae along distomedial to apical margins, with one oblique row of three setae subdistally. Maxilla 2 inner lobe with one oblique row of ten plumose setae on surface. Gnathopods 1 and 2 each possessing carpus with one and two rastellate setae, respectively. Pereopod 6, 1.33 × as long as pereopod 5; coxa anterior lobe with one seta on ventral margin. Sternal gills absent. Epimeral plate 2 ventral margin with two submarginal setae anteriorly, posterodistal corner slightly notched bearing one elongate seta. Epimeral plate 3 ventral margin with three submarginal setae anteriorly, slightly concaved at the middle, posterodistal corner slightly notched bearing one elongate seta. Pleopods rami reduced. Telson cleft for 0.14% of length.

Description.

Holotype female: Body approximately 9.1 mm long. Sternal gills absent (Fig. 13A ).

Head (Fig. 13B ) 1.26 × as long as pereonite 1; rostrum reduced, with minute setae apically; lateral cephalic lobe anteriorly expanded, apex rounded, slightly dilated anteroventrally; antennal sinus not deep; eye absent.

Antenna 1 (Fig. 13C ) 0.33 × as long as body; 1st-3rd peduncular articles length ratio of 1.00: 0.66: 0.37; 1st article stout, posterior margin with one pair of robust setae and one single robust seta; accessory flagellum bi-articulate, last article very reduced; flagellum 1.14 × as long as peduncles, composed of 15 articles, calceoli absent, aesthetascs present from 3rd to 14th articles.

Antenna 2 (Fig. 13D ) 0.59 × as long and more setose than antenna 1; antennal cone well developed, apex rounded; 4th peduncular article margins subparallel, 0.34 × wider than long, posterior margin slightly widening distally and notched at distal corner, 5th article 1.07 × as long as 4th article, three calceoli present on medial surface; flagellum composed of seven articles, 1.13 × as long as 5th peduncular article, single calceoli present from 1st to 3rd articles, aesthetascs absent.

Upper lip (Fig. 13E ) rounded, apex slightly produced apically, covered with minute setae, not notched.

Lower lip (Fig. 13F ) inner lobes indistinct; outer lobes covered with minute setae; mandibular processes developed.

Mandible (Fig. 13G, H ) incisor 5-dentate on both sides; lacinia mobilis tri-cuspidate (two of them finely dentate and one small, produced upwards) on right and 5-dentate on left side; five 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 ten setae medially; 3rd article subfalcate, as long as 2nd article, lined with 18 setae from medial margin to apex.

Maxilla 1 (Fig. 13I ) inner lobe subrhomboid, with four plumose setae on apical margin; outer lobe with seven dentate robust setae; palp bi-articulate, 2nd article apex exceeding apical setae of outer plate, with six robust setae along distomedial to apical margins, with one oblique row of three setae subdistally.

Maxilla 2 (Fig. 13J ) inner lobe slightly shorter but wider than outer lobe, with one oblique row of ten plumose setae on surface and two rows of simple setae on apical margin; outer lobe apical margin with two rows of simple setae.

Maxilliped (Fig. 13K ) inner lobe subrectangular, apex rounded, with six subdentate robust setae mediodistally and with seven plumose setae subapically; outer lobe elongate semicircular, 1.13 × as long as 2nd palp article, with five robust setae and nine plumose setae apical or subapically; inner lobe apex not exceeding middle of 2nd article of palp, with three plumose setae and five dentate robust setae apically; palp composed of four articles; 2nd article with many setae on medial margin; 3rd article slightly dilated distally, 0.5 × as long as 2nd article; 4th article falcate, 0.76 × as long as 3rd article, apical setae 0.75 × as long as 4th article.

Gnathopod 1 (Fig. 14A, B ) coxa subrectangular, 1.43 × wider than long, anterodistal corner somewhat produced, with five setae marginally, ventral margin a little convex; basis obtuse trapezoidal, posteriorly expanded, 0.51 × wider than long, lined with elongate simple setae posteriorly, anterior margin without setae; ischium 0.16 × as long as basis, with small anterior lobe; carpus 0.58 × as long as basis, with two robust seta on anterior margin, carpal lobe not developed, apex rounded with one rastellate seta and many simple or serrate setae; propodus subovate, 1.32 × as long and 1.48 × as wide as basis, posterior margin distal half with four robust setae successively increasing distally, palm irregular, defined by largest lateral seta of posterior margin, finely serrated, lined with six robust setae medially; dactylus as long as palm, inner margin toothed, outer margin with two setae, unguis developed.

Gnathopod 2 (Fig. 14C-E ) as long as gnathopod 1; coxa 1.32 × as long as that of gnathopod 1, 1.22 × wider than long,, anterior and ventral margins not produced, rounded, lined with 15 setae, posterior margin slightly humped proximally; basis posteroproximally expanded, 0.34 × wider than long, lined with elongate simple setae posteriorly, anterior margin without setae; ischium 0.14 × as long as basis, with small anterior lobe; carpus 0.56 × as long as basis, with two pairs of robust and simple setae on anterior margin, carpal lobe not developed, broader than that of gnathopod 1, margin weakly crenulate, with two rastellate setae and many simple or serrate setae; propodus trapezoidal, 1.00 × as long and 1.54 × as wide as basis, anterior margin slightly convex, posterior margin 0.57 × as long as anterior margin, lined with five clusters of elongate setae, with two defining robust setae distally; palm irregular, finely serrated, lined with nine medial and eleven lateral robust setae (two defining setae stouter than others); dactylus as long as palm, inner margin toothed, outer margin with one seta, unguis developed.

Pereopod 3 (Fig. 15A, B ) coxa subrectangular, 1.53 × wider than long, slightly expanded posteroventrally, with six setae anteriorly, ventral margin concave, with three posterior setae; basis expanded, 0.63 × as wider than long, width longest at proximal 1/3, anterior margin lined with minute setae, with one sensory seta, posterior margin with seven elongate setae; merus anterodistally expanded, 0.32 × wider than long, 0.62 × as long as basis, anterodistal corner produced, apex blunt; carpus not expanded, 0.50 × as long as basis; propodus linear, as long as carpus; dactylus 0.40 × as long as propodus, unguis developed.

Pereopod 4 (Fig. 15C, D ) similar to pereopod 3 except that merus 0.88 × as long as that of pereopod 3; different number or position of several setae.

Pereopod 5 (Fig. 15E ) coxa bilobate, anterior lobe larger than posterior lobe, expanded ventrally (0.81 × longer than wide), margin rounded, lined with five simple setae ventrally; posterior lobe with one seta at posterior corner; basis expanded, subrectangular, 0.53 × wider than long, anterior margin slightly convex, lined with five single robust setae, posterior margin more expanded, lined with eleven simple setae, distal corner produced forming an angle; merus posterodistally expanded, 0.42 × as wide and 0.73 × as long as basis, with three pairs of simple setae on anterior margin and two robust setae on posterior margin; carpus subrectangular, posterodistal corner slightly produced, 0.25 × wider than long, 0.61 × as long as basis, with two anterior and one posterior clusters of simple and robust setae, with well-developed distal clusters of setae at both anterior and posterior corners (longest seta 0.31 × as long as propodus); propodus linear, 1.17 × as long as carpus, anterior margin with two clusters of simple and robust setae (longest seta of distal cluster slightly 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 0.31 × as long as propodus, unguis developed.

Pereopod 6 (Fig. 15F, G ) 1.33 × as long as pereopod 5; coxa bilobate, anterior lobe 0.71 × as long as that of pereopod 5, ventral margin with one seta only, posterior lobe expanded backward, with one seta at posterior corner; basis expanded, subrectangular, 1.12 × as long and 1.00 × as wide as that of pereopod 5, 0.49 × wider than long, posterodistal corner produced forming an angle; merus posterodistally expanded, 0.44 × as wide and 0.85 × as long as basis, with three anterior and two posterior setal clusters; carpus rectangular, 0.23 × wider than long, 0.80 × as long as basis, with two setal clusters on anterior and posterior margins, respectively, with well-developed antero- and posterodistal setal clusters (longest seta 0.25 × as long as propodus); propodus linear, 1.09 × 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 0.33 × as long as propodus, unguis developed.

Pereopod 7 (Fig. 15H, I ) 1.01 × as long as pereopod 6; coxa unilobed, subtriangular, 0.83 × as long as that of pereopod 6, posteriorly expanded with one seta at posterior corner, with one seta on ventral margin; basis expanded, subrectangular, 1.09 × as long and 0.93 × as wide as that of pereopod 6, 0.42 × wider than long, posterodistal corner slightly produced but weaker than those of pereopods 6 and 7; merus posterodistally expanded, 0.60 × as wide and 0.70 × as long as basis, with two setal clusters on anterior and posterior margins, respectively; carpus rectangular, 0.26 × wider than long, 0.70 × as long as basis, with one cluster and three clusters of setae on anterior and posterior margins, respectively, with well-developed antero- and posterodistal setal clusters (longest seta 0.25 × as long as propodus); propodus linear, 1.09 × as long as carpus, anterior margin with three setal clusters (longest seta of distal cluster shorter than that of pereopod 6) and one pair of locking robust setae distally, posterior margin with one marginal short seta and one distal cluster of elongate setae (those shorter than that of pereopod 6); dactylus 0.42 × as long as propodus, unguis developed.

Epimeral plate 1 subquadrate, ventral margin without setae, posterior margin convex, lined 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 convex, with four setae, posterodistal corner slightly notched bearing one elongate seta. Epimeral plate 3 larger than plate 2, ventral margin with three submarginal setae anteriorly, slightly concaved at the middle, posterodistal corner slightly notched bearing one elongate seta (Fig. 16A ).

Pleopod 1 (Fig. 16B ) peduncle with one pair of retinaculae mediodistally, one simple seta laterodistally; outer ramus 1.23 × as long as peduncle, composed of eight articles; inner ramus 1.49 × as long as peduncle, composed of seven articles (coalesced 1st article exceeding proximal two articles of outer ramus combined).

Pleopod 2 (Fig. 16C, D ) peduncle 1.10 × as long as that of pleopod 1, with one pair of retinaculae mediodistally and one simple seta laterodistally; reduction of rami different from right and right sides; in left side, outer ramus 0.66 × as long as peduncle, composed of four articles; inner ramus 1.16 × as long as peduncle, composed of six articles (coalesced 1st articles on inner and outer rami equal each other); in right side, both rami more reduced or coalesced.

Pleopod 3 (Fig. 16E ) 0.80 × as long as pleopod 2; peduncle 0.84 × as long as that of pleopod 2, with one pair of retinaculae mediodistally and one seta laterodistally; outer ramus 0.84 × as long as peduncle, composed of six articles; inner ramus 1.06 × as long as peduncle, composed of five articles (coalesced 1st article 1.40 × as long as proximal two articles of outer ramus combined).

Uropod 1 (Fig. 16F ) peduncle with one basofacial seta, with five margin robust setae and one distal seta dorsolaterally, with one distal robust seta dorsomedially; outer ramus 0.51 × as long as peduncle, with one distal robust seta dorsomedially, apical cluster composed of five robust setae (longest seta 0.59 × as long as outer ramus); inner ramus 0.70 × as long as peduncle, with three robust setae dorsomedially and one robust seta dorsolaterally, with three elongate setae on ventral margin subproximally, apical cluster of setae composed of seven robust setae and one sensory seta (longest seta 0.45 × as long as inner ramus).

Uropod 2 (Fig. 16G ) 0.57 × as long as uropod 1; peduncle 0.46 × as long as that of uropod 1, with two marginal robust setae and one distal robust seta dorsolaterally, with one distal robust seta dorsomedially; outer ramus 0.73 × as long as peduncle, with one distal robust seta dorsolaterally, apical cluster composed of five robust setae (longest seta 0.61 × as long as outer ramus, one of those with abnormal apex); inner ramus 1.15 × as long as peduncle, with two robust setae dorsomedially and one robust seta dorsolaterally, apical cluster composed of five robust setae and one sensory seta (longest seta 0.38 × as long as inner ramus).

Uropod 3 (Fig. 16H ) uniramous, 0.76 × as long as uropod 1; peduncle short, 0.62 × as long as uropod 2, with two minute setae on medial margin, with two setal clusters laterodistally; ramus 3.75 × as long as peduncle, bi-articulate, proximal article gradually diminished in width, with four clusters of setae laterally, with two clusters of setae and one single robust seta medially, (longest seta of distal cluster not exceeding distal article ramus), distal article 0.24 × as long as proximal article, with five elongate simple setae apically.

Telson (Fig. 16I ) 0.81 × as wide as long, cleft for 14% of length, each lobe with one pair of penicillate setae dorsally, and one penicillate seta and three robust setae on apex.

Remarks.

Pseudocrangonyx minutus sp. nov. is very similar to P. daejeonensis Lee, Tomikawa, Nakano & Min, 2018 in that the telson is concave (less than 15%) at the apex. However, the lateral cephalic lobe is more produced anteriorly and the antennal sinus is deeper in P. minutus compared to P. daejeonensis ( Lee et al. 2018). In addition, the 2nd peduncular article of antenna 1 is 0.66 times as long as 1st article (compared to 0.5 times in P. daejeonensis ), the flagellum of antenna 1 is composed of 15 articles (compared to ten articles in P. daejeonensis ), antenna 2 has calceoli on the medial surface of the 5th peduncular article and the 1st-3rd flagellum articles (which are absent in P. daejeonensis ), the flagellum of antenna 1 is composed of seven articles (compared to four articles in P. daejeonensis ), eight raker setae are present on each mandible (compared to three on left and two on right in P. daejeonensis ), the mandibular palp is more setose, the inner lobe of maxilla 1 has four plumose setae on the apical margin (compared to two plumose setae in P. daejeonensis ), the 2nd article of palp maxilla 1 shows six dentate robust setae apically (two dentate robust setae in P. daejeonensis ), and the outer plate of the maxilliped is larger ( Lee et al. 2018). Moreover, in P. minutus , each basis of gnathopods 1 and 2 is more setose posteriorly and each propodus is less expanded posteriorly, pereopods 3 and 4 are also more setose, each propodus of pereopods 5-7 is slender and has more robust setae than that of P. daejeonensis , each posterior margin of the bases in pereopods 5-7 has a smooth or smaller angle at the distal corner, each propodus of pereopods 5-7 is more slender and elongate. Lastly, in P. minutus sp. nov., the peduncle of uropod 1 has five robust setae marginally on the dorsolateral margin (compared to two robust setae in P. daejeonensis ) and the inner ramus of uropod 1 has three elongate simple setae proximally on the ventral margin (compared to one seta in P. daejeonensis ) ( Lee et al. 2018).

Pseudocrangonyx minutus sp. nov. is also similar to P. komaii Tomikawa & Nakano, 2018 from Japan with regard to general shape and length ratio of the articles in the gnathopods and pereopods, the reduced number of the articles of rami in the pleopods, and the slightly concave shape of the telson (less than 15%) at the apex. On the other hand, P. minutus sp. nov. can be readily distinguished from P. komaii by the slender and elongate peduncular articles of antennae 1 and 2, the six apical robust setae in the palp of maxilla 1 (compared to four in P. komaii ), by one and two rastellate setae in gnathopods 1 and 2, respectively (which are absent in P. komaii ), by a more setose posterior margin of the basis in each gnathopod, by the presence of five setae ventrally on the anterior lobe of coxa 5 (compared to one in P. komaii ), and by the more expanded basis of pereopod 5 ( Tomikawa and Nakano 2018).

Figures

Figure 13. Pseudocrangonyx minutus sp. nov. Holotype: female, NIBRV 0000862810, 9.1 mm, from Gageo Is., 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 K maxilliped.

Figure 14. Pseudocrangonyx minutus sp. nov. Holotype: female, NIBRV 0000862810, 9.1 mm, from Gageo Is., South Korea. A gnathopod 1 B rastellate setae and palm of gnathopod 1 C gnathopod 2 D rastellate setae of gnathopod 2 E palm of gnathopod 2.

Figure 15. Pseudocrangonyx minutus sp. nov. Holotype: female, NIBRV 0000862810, 9.1 mm, from Gageo Is., South Korea. A pereopod 3 B coxal gill of pereopod 3 C pereopod 4 D coxal gill of pereopod 4 E pereopod 5 F pereopod 6 G coxal gill of pereopod 6 H pereopod 7 I coxal gill of pereopod 7.

Figure 16. Pseudocrangonyx minutus sp. nov. Holotype: female, NIBRV 0000862810, 9.1 mm, from Gageo Is., South Korea. A epimeral plates and urosomites B pleopod 1, left C pleopod 2, left D pleopod 2, right E pleopod 3, left F uropod 1 G uropod 2 H uropod 3 I telson. Abbreviations: Ep, epimeral plate; ir, inner ramus; and or, outer ramus.