Pseudoleucon japonicus Gamô, 1964

Lee, Sung-Hyun Kim and Chang-Mok, 2021, A new record of Pseudoleucon japonicus (Crustacea: Cumacea: Leuconidae) from Korea, Journal of Species Research 10 (1), pp. 72-77 : 73-76

Pseudoleucon japonicus Gamô, 1964 ( Figs. 1 , 2 )

ḎǨṞỢḆḝḑNjẹ (ljḍ)

Pseudoleucon japonicus Gamô, 1964: 246 , figs. 4, 5; 1967: 162; Watling, 1991: 578.

Material examined. Korea: 1 sub ♂ (NIBRIV0000299 463) 1 subg (DKUCUM 202001), EEZ st. D6, 35°19′ 31.0″N, 124°58′08.5″E, 22 April 2008, collected by Song SJ ; 1 subg(DKUCUM 202002), EEZ st. 1, 35°47′40.2″N, 125°05′43.3″E, 13 August 2007, collected by Song SJ; 1 subg(DKUCUM 202003), EEZ st. N2, 35°41′31.0″N 125°28′37.7″E, 30 January 2008, collected by Song SJ; 1 subg(DKUCUM 202004), EEZ st. 14, 35°02′43.6″N, 124°46′26.7″E, 22 April 2008, collected by Song SJ.

Description. Subadult male (NIBRIV0000299463). Body length ( Fig. 1A ) 2.6 mm, excluding uropods. Carapace ( Fig. 1A, B ) slightly longer than 1/3 of body length, 1.7 times as long as its depth, 1.6 times as long as its width; shape nearly rectangular in dorsal view, with 1 pair of short oblique ridges, ridges beginning near end of frontal lobe and merging with dorsal median carina. Antennal notch and antero-lateral angle indistinct. Antero-lateral margin with strong serrations. Pseudorostral lobes ( Fig. 1A, B ) extending anterodorsally, truncated, and serrated. Ocular lobe ( Fig. 1A, B ) very small, without lens and pigment. Pereon ( Fig. 1A, B ) 0.7 times carapace length, shorter than 1/3 of body length. Pleon ( Figs. 1A , 2F ) 0.6 times as long as carapace and pereon together, with 2 pairs of pleopods; pleonite 5 longest, 0.7 times as long as pleonites 3 and 4 together; pleonite 6 0.5 times as long as pleonite 5, with 3 pairs of simple setae near distal margin. Antenna 1 ( Fig. 1C ), peduncle 3-articulated; article 1 subequal in length to remaining articles combined, with 1 short plumose and 6 plumose setae; article 2 0.5 times as long as article 1, with 2 simple setae bearing a bundle of hairs laterally, 10 simple setae bearing a bundle of hairs distally; article 3 subequal in length to article 2, with 5 simple setae bearing a bundle of hairs on medial corner. Main flagellum 3-articulated, subequal in length to article 3 of peduncle; article 1 longest, with 1 simple seta bearing a bundle of hairs distally; article 2 0.4 times as long as article 1, with 1 aesthetasc and 2 simple setae bearing a bundle of hairs distally; article 3 small, with 1 aesthetasc and 2 simple setae bearing a bundle of hairs distally. Accessory flagellum not articulated, with 5 simple setae bearing a bundle of hairs distally.

Antenna 2 ( Fig. 1D ), peduncle composed of 4 articles; article 2 with 2 plumose setae anterior margin; article 3 with 1 plumose seta anterior margin; article 4 without seta; flagellum underdeveloped.

Maxilliped 3 ( Fig. 1E ), basis 1.2 times as long as remaining articles combined, with numerus hair-like and 4 plumose setae medially, 4 plumose setae on lateral face, 1 plumose and 3 long plumose setae on lateral conner; ischium short, unarmed; merus 2.6 times as long as ischium, with 2 plumose setae medially, 1 long plumose seta laterodistally; carpus 1.2 times as long as merus, with 3 plumose setae medially; propodus 0.8 times as long as carpus, unarmed; dactylus 0.9 times as long as propodus, with 4 short simple setae on lateral face, 5 simple setae terminally.

Pereopod 1 ( Fig. 1F ), basis 0.9 times as long as remaining articles combined, with 5 plumose setae medially, 4 plumose setae on lateral face, 1 plumose seta and 3 simple setae bearing a bundle of hairs distally; ischium very short, with 1 plumose seta medially; merus 2.9 times as long as ischium, with 1 short simple and 1 plumose setae medially, 2 short simple and 3 long plumose setae laterally; carpus 1.4 times as long as propodus, with 2 short simple setae, 1 complex pedunculate seta, and 4 simple setae bearing a bundle of hairs medially, 4 short simple and 4 long plumose setae laterally, 2 short simple and 3 long plumose setae laterodistally; propodus 0.8 times as long as carpus, with 4 short simple setae and 1 simple seta bearing a bundle of hairs medially, 4 short simple and 3 long plumose setae laterally; dactylus 0.8 times as long as propodus, with 2 short simple and 1 simple setae laterally, 1 short simple and 3 simple setae terminally.

Pereopod 2 ( Fig. 2A ), basis 1.3 times as long as remaining articles combined, with 12 plumose setae and 3 simple setae bearing a bundle of hairs medially, 1 plumose seta on lateral face, 1 short simple and 1 plumose setae laterally; ischium very short, with 1 long plumose seta mediodistally; merus 7.3 times as long as ischium, with 1 simple seta bearing a bundle of hairs mediodistally, 3 simple setae bearing a bundle of hairs laterally, 1 plumose seta distally; carpus 1.4 times as long as merus, with 2 simple setae bearing a bundle of hairs medially, 2 simple setae bearing a bundle of hairs laterally, 1 plumose seta and 2 simple setae bearing a bundle of hairs distally; propodus 0.3 times as long as carpus, with 1 simple seta bearing a bundle of hairs laterodistally; dactylus 2.9 times as long as propodus, with 1 short simple and 1 plumose setae medially, 2 simple setae bearing a bundle of hairs on lateral face, 1 simple seta bearing a bundle of hairs laterally, 1 simple seta and 5 simple setae bearing a bundle of hairs terminally.

Pereopod 3 ( Fig. 2B ) basis 1.7 times as long as remaining articles combined, with 10 plumose setae medially, 2 plumose setae on lateral face, 1 plumose and 2 long plumose setae laterodistally, 1 plumose and 1 long plumose setae distally; ischium 0.1 times as long as basis, with 1 plumose seta medially, 1 plumose and 1 annulate setae distally; merus subequal in length to ischium, with 1 annulate seta distally; carpus 1.9 times as long as merus, with 1 simple seta bearing a bundle of hairs laterally, 1 short simple and 3 annulate setae distally; propodus 0.6 times as long as carpus, with 1 annulate seta laterodistally; dactylus 0.3 times as long as propodus, with 2 short simple and 1 annulate setae terminally.

Pereopod 4 ( Fig. 2C ), basis 1.7 times as long as remaining articles combined, with 1 plumose seta medially, 3 plumose setae on lateral face, 1 plumose seta laterally, 1 plumose and 2 long plumose setae distally; ischium 0.1 times as long as basis, with 4 annulate setae distally; merus 1.6 times as long as ischium, with 1 plumose and 1 annulate setae distally; carpus 1.7 times as long as merus, with 1 annulate seta laterally, 1 short simple and 3 annulate setae distally; propodus 0.5 times as long as carpus, unarmed; dactylus 0.2 times as long as propodus, with 2 short simple and 1 annulate setae terminally.

Pereopod 5 ( Fig. 2D ), basis 0.8 times as long as remaining articles combined, with 3 plumose setae mediodistally, 2 plumose setae and 1 simple seta bearing a bundle of hairs laterally; ischium 0.3 times as long as basis, with 3 annulate setae medially; merus 1.9 times as long as ischium, with 1 plumose seta laterally, 1 annulate seta distally; carpus subequal in length to merus, with 1 plumose seta laterally, 4 annulate setae distally; propodus 0.5 times as long as carpus, with 1 annulate seta laterodistally; dactylus 0.2 times as long as propodus, with 1 short simple seta medially, 1 annulate seta terminally.

Pleopod 1 ( Fig. 2E ), basis 2.5 times as long as inner ramus, unarmed; outer ramus 2-articulated, with 4 simple setae terminally; inner ramus unarticulated, with 2 complex pedunculate setae laterally, 4 simple setae terminally.

Uropod ( Fig. 2F ), peduncle subequal in length to last pleonite, with 1 simple seta and 7 simple setae bearing a bundle of hairs medially, 1 short simple seta laterally. Uropod endopod 2-articulated, 1.4 times as long as peduncle, 0.7 times as long as exopod; article 1 with 4 plumose setae and 1 simple seta with single subterminal setule medially, 1 plumose seta and 1 simple seta bearing a bundle of hairs mediodistally, 1 short simple seta laterally; article 2 0.4 times as long as article 1, with 1 short simple seta and 1 simple seta with single subterminal setule mediodistally, 1 short simple seta laterodistally, 1 long plumose and 1 stout simple setae terminally. Uropod exopod 2-articulat- ed, 1.9 times as long as peduncle; article 1 unarmed, article 2 with 3 plumose setae, 1 broken seta, and 21 simple seta bearing a bundle of hairs.

Subadult female (DKUCUM 202001). Body length ( Fig. 1G ) 2.7 mm, excluding uropods. Carapace slightly longer than 1/3 of body length, 1.5 times as long as its depth; shape and sculpture of carapace similar to subadult male. Pereon 0.7 times as long as carapace, shorter than 1/3 of body length; pereopods 4 and 5 without exopod. Pleon 0.6 times as long as carapace and pereon together, without pleopod.

Distribution. Korea (Yellow Sea), Japan.

Remarks. Pseudoleucon japonicus Gamô, 1964 is easily distinguished from Pseudoleucon sorex Zimmer, 1903 by having a pair of short oblique ridges on the carapace. In the original description, only the female of P. japonicus was described ( Gamô, 1964). Fortunately, the specimens of both sexes were collected in the present study. There is no doubt that these specimens are P. japonicus due to the following characters: 1) the carapace has strong serrations on antero-lateral margin and a pair of short oblique ridges on the side surface; 2) the short oblique ridges begin near the end of frontal lobe and merge with dorsal median carina; 3) the antenna 1, pereopod 2 and uropod have a lot of simple setae decorated with a bundle of hairs at the end. Also, the setal type and pattern of appendages, such as antenna 1, maxilliped 3, pereopods 1 - 5 and uropod, are almost the same as Gamô̓s specimen. There is, however, a slight dif- ference in the length ratio of the pereopods and uropods, between the collected specimens and the original description ( Gamô, 1964), which is assumed to be due to sexual dimorphism and developmental variation.

Figures

Fig. 1. Pseudoleucon japonicus Gamô, 1964, subadult male, 2.6mm.A, habitus, lateral view; B, carapace and pereon, dorsal view; C, antenna 1; D, antenna 2; E, maxilliped 3; F, pereopod 1; G, habitus of subadult female, lateral view, 2.7mm. Scale bars:A, B, G=0.5 mm, C-F=0.2mm.

Fig. 2. Pseudoleucon japonicus Gamô, 1964, subadult male, 2.6 mm.A, pereopod 2; B, pereopod 3; C, pereopod 4; D, pereopod 5; E, pleopod 1; F, uropods and last pleonite. Scale bars:A-C, F=0.2 mm, D, E=0.1 mm.