Pentias pluriarticulatus, Kim & Jung & Yoon, 2020

Kim, Sung Hoon, Jung, Tae Won & Yoon, Seong Myeong, 2020, Two new species of idoteid isopods (Crustacea, Isopoda, Idoteidae) from Korea, Zootaxa 4858 (2), pp. 186-200 : 192-199

Pentias pluriarticulatus sp. nov.

Figs 4–7

Material examined. Holotype: 1 ♂, 18.4 mm, intertidal rocky shore at Seokbyeong-ri (36°1′15″N, 129°34′51″E), Guryongpo-eup , Nam-gu, Pohang-si, Gyeongsangbuk-do, Korea, 30 September 2017, NIBRIV0000862801.

Paratype: 1 ♂, 14.3 mm, same location as the holotype .

Additional material: 1 ♂, 15 mm, Yeondo Island , Yeondo-ri, Nam-myeon Yeosu-si Jeollanam-do, Korea, (34°26´31″N, 127°48´43″E), 29 June 2017, 10 m, SCUBA diving ; 1 ♀ (non-ovigerous), 15.3 mm, Geomun-ri , Samsan-myeon (34°03´04″N, 127°35´13″E), 28 June 2017, 10 m, SCUBA diving .

Diagnosis. Body elongated; lateral margins parallel; cephalon with concave anterior margin possessing small median notch; longitudinal line on both lateral margins crossing eye; eye large; coxal plates invisible dorsally on pereonites 2–4, whereas visible on pereonites 5–7; pleon without articulating pleonite; pleonites composed of single segment with 3 partial sutures; pleotelson gradually tapering posteriorly; apex rounded; posterolateral region angled. Flagellum of antenna 9-articled. Uropodal endopod sinuous distally.

Description of holotype male. Body ( Fig. 4A, B ) slender, elongated oval, smooth, 18.4 mm, 7.4 times longer than wide; lateral margins parallel; color white in alcohol. Cephalon 0.9 times as long as wide; anterior margin slightly concave possessing small median notch; posterior margin emarginated to pereonite 1; longitudinal line on both lateral margins crossing eye; eye large, located at lateral margin. Pereon smooth; pereonites 2–5 subequal in length; pereonites 6 and 7 shorter than preceeding segments. Coxal plates invisible dorsally on pereonites 2–4, whereas visible on pereonites 5–7, sequentially longer; coxal plates 2–4 extended half of pereonites; coxal plates 5 and 6 extended over two-thirds of pereonites; coxal plate 7 extended whole lateral margin of pereonite. Pleon composed of a single segment with 3 partial sutures; pleotelson one-third of body length, gradually tapering posteriorly, apex rounded, posterolateral region angled.

Antennula ( Fig. 5A ) short, reaching to distal end of peduncular article 2 of antenna, composed of 3 peduncular articles and single-articled flagellum; peduncular article 1 globular, greatly dilated; article 2 cylindrical, with 1 anterolateral and 1 lateral penicillate seta; article 3 slightly longer than article 2 in length; flagellum oval, with 9 aesthetascs along with lateral margin. Antenna ( Fig. 5B, C ) consisting of 5 peduncular articles and multi-articulated flagellum; peduncular articles sequentially longer in length; article 1 short and barely visible on dorsal side; article 2 1.7 times longer than article 1; articles 3 and 4 subequal in length; article 5 longest in length; flagellum composed of 9 articles, with 2–4 simple setae on distal end of each article; last article with numerous simple setae at distal end.

Left mandible ( Fig. 5D ), incisor strongly 3 toothed, sclerotized; lacinia mobilis 2 toothed, with 1 denticulated seta; molar process rounded, with many short bristles. Right mandible ( Fig. 5E ), incisor weakly 4 toothed, sclerotized; lacinia mobilis 3 toothed with 3 denticulate setae; molar process rounded, with many short bristles.

Maxillula ( Fig. 5F ) with fine setae on lateral margin, consisting of 2 lobes; inner lobe with 2 simple setae on subapical region, 3 long plumose setae on apical region; outer lobe with 6 smooth robust and 8 denticulate robust setae apically. Maxilla ( Fig. 5G ) with fine setae laterally, composed of 3 lobes; inner lobe with 5 long plumose setae apically; mesial lobe with 4 denticulate setae on apical margin; outer lobe with 4 denticulate setae apically. Maxilliped ( Fig. 5H ), endite reaching to half of palp article 3, with 4 plumose setae and 3 robust setae on apical region, with 1 coupling hook on inner margin; palp 5-articled; article 1 small, without setae; article 2 with 5 simple setae along with lateral margin and 4 short simple setae on mesial margin, article 3 with numerous simple setae on anterodistal angle and 2 short simple setae on mesial margin; article 4 with 8 simple setae on inner margin and 1 simple seta on outer margin; article 5 with 9 simple setae apically.

Pereopod 1 ( Fig. 6A ) slender; basis stout; ischium 0.4 times as long as basis in length; merus almost square, shorter than ischium, with 2 simple setae on inferior margin; carpus triangular, with 3 simple setae on inferior margin; propodus rectangular, with 20 comb setae on palmar surface, 6 simple setae on ventral margin; dactylus bi-unguiculate, with 7 simple setae apically.

Pereopod 2 ( Fig. 6B ), basis stout, with 1 penicillate seta on superior margin; ischium slander than basis, with 2 simple setae on inferior margin; merus almost square; carpus triangular, with 1 simple seta on inferior margin; propodus with 7 simple setae on inferior margin; dactylus bi-unguiculate, with 12 simple setae apically.

Pereopods 3–7 ( Fig. 6 C–G) similar to pereopod 2; basis with 1–2 penicillate setae on superior margin; ischium with 0–1 simple seta on inferior distal angle; carpus with 1–2 simple setae on inferior distal angle; propodus with 1–3 simple setae on inferior margin and 3 or 5 simple setae on inferior distal margin; dactylus bi-unguiculate, with 4–5 simple setae on superior distal margin and 4–7 simple setae on inferior distal margin.

Penes ( Fig. 4D ) paired and parallel, not fused at base.

Pleopod 1 ( Fig. 7A ), protopod with 5 coupling hooks on inner margin, 6 plumose setae on outer margin; rami lanceolate, with numerous plumose setae on lateral and distal margins; exopod with 1 penicillate seta on distal end; endopod slightly longer than exopod.

Pleopod 2 ( Fig. 7B ), protopod with 4 coupling hooks on inner margin and 3 plumose setae on outer margins; rami with numerous plumose setae on lateral and distal margin; endopod longer than exopod; appendix masculina longer than endopod, with serrated margin on distal region.

Pleopod 3 ( Fig. 7C ), protopod with 4 coupling hooks on inner margins; endopod longer than exopod, naked; exopod with numerous plumose setae on distal and outer margin.

Pleopod 4 ( Fig. 7D ), protopod with 2 plumose setae on outer margin; rami subequal in length; endopod naked; exopod with short simple setae along with outer margin.

Pleopod 5 ( Fig. 7E ) similar to pleopod 4; protopod with 1 plumose on outer margin.

Uropod ( Fig. 7F ) uniramous; protopod longer than width, with 3 plumose setae on distal end; endopod 0.3 times as long as protopod; distal end sinuous.

Variation. The longitudinal line on the lateral margins crossing eyes extends to pereonites depending on the specimens.

Distribution. Korea (Southern coast of the Korean Peninsula).

Remarks. Pentias pluriarticulatus sp. nov. is readily distinguishable from its congeners by the following features combined: (1) the lateral margins of the body are parallel; (2) the anterior margin of the cephalon has a small median notch; (3) the eye is large; (4) coxal plates 5–7 are visible, but plates 2–4 are invisible in dorsal view; (5) the flagellum of the antenna is composed of nine articles; (6) the pleon consists of three partial sutures without articulating pleonite; (7) the pleotelson is gradually tapering posteriorly and has an angled posterolateral region; and (8) the uropodal endopod is sinuous distally ( Richardson 1904; Collinge 1916; Rafi 1973; Nunomura 2006; Song & Min 2015). The new species differs from P. hayi in that the body is parallel laterally (vs. convex laterally in the latter) and coxal plates 2–4 is visible dorsally (vs. invisible in the latter) ( Richardson 1904; Song & Min 2015). Pentias pluriarticulatus sp. nov. is also easily distinguishable from the P. thompsoni by having three incomplete sutures (vs. one complete and two incomplete sutures in the latter) ( Collinge 1916; Song & Min 2015). Pentias pluriarticulatus sp. nov. resembles P. namikawai by having parallel lateral margins of the body, but the former can be distinguished from the latter in that the distal end of the uropodal endopod is sinuous, while it is rounded in the latter ( Nunomura 2006). Within the genus, Pentias pluriarticulatus sp. nov. is most similar to P. arimotoi by having elongated body, pleon composed of a single-segmented pleonite with three partial sutures, and pleotelson tapering posteriorly. However, the new species differs from P. arimotoi in terms of the parallel lateral margins of the body in the former (vs. slightly convex in the latter), large eye in the former (vs. small eye in the latter), coxal plates 5–7 observable on the dorsal side in the former (vs. coxal plates not observable on the dorsal side in the latter), nine-articled flagellum of the antenna in the former (vs. six-articled in the latter), and posterolateral angle of the pleotelson (angled in the former vs. not angled in the latter ( Rafi 1973). The detailed comparison of Pentias species is presented in table 2.

Etymology. The specific name, pluriarticulatus , originates from the combination of the Latin words pluris, meaning “more,” and articulatus, meaning “jointed.” This name refers to that this species has a more articulated flagellum of the antenna than its congeners.

Figures

FIGURE 4. Pentias pluriarticulatus sp. nov., holotype, male. A, Habitus, dorsal view; B, Habitus, lateral view; C, Cephalon; D, Pereonite 7 to pleotelson, ventral view. Scale bars: A, B = 5 mm, C, D = 1 mm.

FIGURE 5. Pentias pluriarticulatus sp. nov., holotype, male. A, Antennula; B, Antenna; C, Distal end of the antenna; D, Left mandible; E, Right mandible; F, Maxillula; G, Maxilla; H, Maxilliped. Scale bars: A, C = 0.1 mm, B = 0.5 mm, D–H = 0.2 mm.

FIGURE 6. Pentias pluriarticulatus sp. nov., holotype, male. A, Pereopod 1; B, Pereopod 2; C, Pereopod 3; D, Pereopod 4; E, Pereopod 5; F, Pereopod 6; G, Pereopod 7. Scale bar: A–G = 0.5 mm.

FIGURE 7. Pentias pluriarticulatus sp. nov., holotype, male. A, Pleopod 1; B, Pleopod 2; C, Pleopod 3; D, Pleopod 4; E, Pleopod 5; F, Uropod. Scale bars: A–F = 1 mm.