Janiralata truncata, Kim & Kim & Yoon, 2022

Kim, Sung Hoon, Kim, Jong Guk & Yoon, Seong Myeong, 2022, Description of two new janirid isopods (Isopoda, Asellota, Janiridae) from Korean waters, Zootaxa 5178 (6), pp. 532-546 : 539-540

Janiralata truncata sp. nov.

Figs 4 and 5

urn:lsid:zoobank.org:act:A4872498-E00D-457B-BBB2-21EE0E344925

Material examined. Holotype: ♂, 2.8 mm, Yeomi-ri (34°22′33″N, 126°00′07″E), Jodo-myeon, Jindo-gun, Jeollanam-do, Korea, 13 April 2018, 5–10 m, SCUBA diving, NIBRIV0000897185.

Paratype: 1 ♀, same location as holotype, 12 April 2018, NIBRIV0000895340 .

Additional material: 1 ♂, Dokgeodo-ri (34°17′29″N, 126°03′42″E), Jodo-myeon, Jindo-gun, Jeollanam-do, Korea, 17 April 2018, 10 m, Smith-McIntyre grab .

Diagnosis. Cephalothorax lacking rostrum, with anterolateral projections; all coxal plates of pereonites visible dorsally; pleotelson truncated distally, with a pair of shallow concavities distally and small, convex medial apex; carpus of pereopod Ⅰ with 14 robust setae along ventral margin; distal end of male pleopod Ⅰ expanding laterally, with a pair of small rounded projections distally near the fusion line of the two first pleopods; exopod of pleopod III with 2 plumose setae on distomedial margin.

Description of holotype male. Body ( Fig. 5A ) smooth, with parallel lateral margins; chromatophores dark brown, scattered dorsally. Cephalothorax 1.9 times wider than long; anterior margin slightly convex, without rostrum; anterolateral margin concave, with anteriorly expanding projections; lateral margin slightly narrowing anteriorly, with simple marginal setae along with margin; eyes positioned dorsally, globular. Pereonites compact, with simple setae laterally; pereonite 1 subacute laterally; pereonites 2 and 3 bilobed laterally, but not deeply concave; pereonite 4 narrowing posteriorly, subacute anterolaterally; pereonite 5 rounded laterally; pereonite 6 rounded laterally, with slightly concave posterior margin; posterolateral margin of pereonite 6 slightly expanding posteriorly, rounded distally; pereonite 7 rounded laterally, expanding posterolaterally bearing acute distal end. Coxal plates of pereonites visible dorsally, with 1 simple seta distally; coxal plate Ⅰ tapering and acute distally; coxal plates II–IV bilobed while coxal plates Ⅴ–VII not lobed; coxal plate IV with distinctly larger anterior lobe than posterior lobe; coxal plate VII surrounded by posterolateral margin of pereonite 7 and pleotelson, slightly visible posterolaterally. Pleon ( Fig. 5A, B ) composed of 1 free pleonite and otherwise fused pleotelson; pleotelson oval to globular, wider than long, with simple setae laterally; posterior margin of pleotelson truncated, slightly concave at uropod insertions, with small and convex medial apex.

Antennula ( Fig. 5C ) composed of 3 peduncular articles and 11 flagellar articles; peduncular article Ⅰ with 3 simple setae laterally, and 3 robust setae and 1 penicillate seta distally; article II oval, with 1 simple seta and 1 penicillate seta laterally, 5 simple setae and 3 penicillate setae distally; article III almost 0.7 times as long as article II, with 3 simple setae distally; flagellar article Ⅰ wider than long, with 2 simple setae distally; articles II–IX with 0–4 simple setae distally; articles IV, Ⅴ, and VIII with 1 aesthetasc distally; articles Ⅹ and XI minute, with simple setae and 1 or 2 aesthetascs distally. Antenna ( Fig. 5D ) subequal to pereon in length, reaching pereonite 4, consisting of 6 peduncular articles and 42 flagellar articles; peduncular article Ⅰ with 2 robust setae laterally; article II shorter than article Ⅰ, with 1 robust seta distally; article III with 2 simple setae, 1 robust seta, and 1 scale laterally, and 1 simple seta and 1 robust seta distally; scale tapering distally, with 1 robust seta and 3 simple setae on distal region; article IV subequal to article II in length, with 3 simple setae and 1 robust seta distally; articles Ⅴ and VI elongated oblong, similar to each other in length, with simple setae and penicillate setae on lateral and distal margins; flagellar article Ⅰ almost 0.4 times as long as peduncular article VI, much longer than other flagellar articles; following articles rectangular, with 0–3 short simple setae distally.

Mandibles ( Fig. 5E, F ), molar process truncated and stepped distally, with 3 simple setae distally; palp article Ⅰ about 0.6 times as long as article II, with 0–2 simple setae distally; palp article II longer than other articles, with 3 short robust setae, 1 long robust seta, and 1 serrate seta laterally; article III curved outward, with robust setae along with lateral margin. Right mandible ( Fig. 5E ), incisor with 5 cusps; setal row composed of 12 serrate setae. Left mandible ( Fig. 5F ), incisor with 3 cusps; lacinia with monocusp; setal row consisting of 8 serrate setae. Maxillula ( Fig. 5G ), inner lobe slender than outer lobe, with 3 serrate setae and numerous fine setae distally; outer lobe with 13 serrate distal setae and numerous fine setae on lateral and medial margins. Maxilla ( Fig. 5H ), inner lobe stouter than other lobes with numerous fine setae laterally, 9 serrate setae distally; mesial lobe with numerous fine setae laterally and 3 serrate setae distally; outer lobe with numerous fine setae laterally, and 3 serrate setae and 1 simple seta distally. Maxilliped ( Fig. 5I ), basis oblong, 1.6 times longer than wide; endite over palp article II, oblong to semicircular, straight inwardly, rounded outwardly, with 3 coupling hooks on medial margin and 10 serrate setae on distal end; palp article Ⅰ trapeziform, expanding distolaterally; lateral margin 4.6 times longer than medial margin; palp article II broadening distally, 0.9 times as long as widest width, with simple setae on medial margin; palp article III oblong, about 0.6 times as long as wide, with simple setae on medial margin; palp articles IV and Ⅴ much slender than articles Ⅰ–III, with numerous simple setae distally; epipod triangular, 1.4 times longer than basis, reaching palp article III, tapering distally, with subacute apex.

Pereopods ( Fig. 6A–D ) slender; basis elongated oblong, about 1.4 times longer than ischium; ischium convex dorsally, with robust setae on dorsal margin; merus expanding distodorsally, with simple setae and robust setae distodorsally; carpus elongated and longer than other articles; dactylus short. Pereopod Ⅰ ( Fig. 6A ), carpus slightly swollen, 2.6 times longer than wide, with 14 robust setae along with ventral margin; propodus, inferior margin proximally serrated; dactylus with 2 claws. Pereopods II, III, and VII ( Fig. 6B–D ) similar with each other; basis with 1–3 penicillate setae dorsally; carpus with 0 or 1 penicillate seta distodorsally; propodus with 1 penicillate seta distodorsally; dactylus with 3 claws.

Pleopod Ⅰ ( Fig. 6E ) about 1.3 times longer than distal wide; lateral margin concave mesially; proximolateral margin rounded; distal end with simple setae and a pair of small rounded projections distally near the fusion line of the two first pleopods; lateral expansion subacute distally. Pleopod II ( Fig. 6F ), protopod oval to oblong, 1.5 times longer than maximal wide, with simple setae distally; endopod located at 0.5 length of protopod; exopod short, curved inwardly; appendix masculina tapering and subacute distally, reaching to distal end of protopod. Pleopod III ( Fig. 6G ), rami consisting of 2 articles; endopod oval to oblong, 1.9 times longer than wide, with 3 plumose setae on distal end; exopod 2.8 times wider than endopod, over distal end of endopod, with 3 simple setae and 2 plumose setae on distomedial margin. Pleopod IV ( Fig. 6H ) biramous; rami tapering distally, with subacute distal end; endopod 1.8 times wider than exopod; exopod slightly shorter than endopod. Pleopod Ⅴ ( Fig. 6I ) uniramous, tapering distally.

Uropod ( Fig. 6J ) 0.9 times as long as pleotelson, protopod oblong, wider posteriorly, 2.1 times longer than maximal wide, with simple setae dorsally and distally; rami elongated oval to oblong about 5.5 time longer than wide, rounded distally, with simple setae along with border; endopod with 7 penicillate setae on lateral margin; exopod almost 0.7 times as long as endopod.

Paratype female. Female resembles the male except for pleopod II. Pleopod II ( Fig. 6K ) globular, about 0.9 times as long as wide, with short simple setae marginally; distal end with distinct concavity.

Remarks. According to the criterion mentioned in the introduction, Janiralata truncata sp. nov. can be assigned into the fourth group based on the presence of plumose setae on the exopod of pleopod III (Wilson & Wägele 1994). Within group D which includes eleven species, the new species mostly resembles three species, J. chuni Thielemann, 1910 , J. davisi Menzies, 1951 , and J. shiinoi Kussakin, 1962 , in lacking posterolateral points and distal concavity ( Thielemann 1910; Menzies 1951b; Wilson & Wägele 1994; Shimomura 2006). However, the former can be easily distinguished from the latter species by the following characteristics: (1) coxal plates of pereonites 2–4 are visible dorsally (vs. invisible dorsally); (2) the distal region of the pleotelson is truncated and slightly concave (vs. not truncated and convex); (3) the carpus of pereopod Ⅰ has 14 robust setae (vs. six in J. chuni and eight in J. shiinoi ); (4) pleopod Ⅰ has a pair of small rounded projections distally (vs. lacking in J. chuni and J. shiinoi ); (5) female pleopod II is concave distally (vs. rounded in J. shiinoi ); and (6) the exopod of pleopod III has fewer plumose setae (two plumose setae in the new species vs. five in J. davisi , eleven in J. chuni , and 16 in J. shiinoi ) ( Thielemann 1910; Menzies 1951b; Kussakin 1962; Shimomura 2006). Additionally, the new species is similar to J. kurilensis Kussakin, 1962 , J. koreaensis , and J. sagamiensis in habitus and morphology of details. However, the new species is easily distinguishable from all the latter species in terms of the Cephalothorax lacking rostrum (vs. having rostrum in J. kurilensis ), the distal region of pleotelson (truncated in the new species vs. concave in J. kurilensis vs. rounded in J. koreaensis and J. sagamiensis ), and the exopod of pleopod III having plumose setae (vs. lacking plumose setae in the latter species) ( Kussakin 1962, 1988; Jang 1991; Shimomura 2006).

Etymology. The specific name truncata originates from the Latin word truncatus, meaning “shorten by cutting off”. This name refers to the shape of the pleotelson that is truncated on the posterior margin. It is nominative singular; gender, feminine.

Distribution. Korea (southern coast of the Korean Peninsula)

Figures

FIGURE 4. Caecijaera ciliata sp. nov., holotype male (A–F) and paratype female, NIBRIV0000876680 (G).A, C–E, Pleopods Ⅰ–IV, respectively; B, Distal end of pleopod Ⅰ; F, Uropod; G, Pleopod II. Scale bar: A, C–G = 0.2 mm, B = 0.05 mm.

FIGURE 5. Janiralata truncata sp. nov., holotype male, NIBRIV0000897185. A, Habitus, dorsal view; B, Pleotelson; C, Antennula; D, Antenna; E, Right mandible; F, Left mandible; G, Maxillula; H, Maxilla; I, Maxilliped. Scale bars: A = 1 mm, B–I = 0.2 mm.

FIGURE 6. Janiralata truncata sp. nov., holotype, male (A–J) and paratype female, NIBRIV0000895340 (K). A–D, Pereopods Ⅰ–III and VII, respectively; E–I, Pleopods Ⅰ–Ⅴ, respectively; J, Uropod; K, Pleopod II. Scale bar: A–K = 0.2 mm.