Idarcturus trispinosus, Kim & Yoon, 2021

Kim, Sung Hoon & Yoon, Seong Myeong, 2021, Four new species of isopods (Crustacea, Isopoda) from South Korea, ZooKeys 1010, pp. 133-164 : 133

Idarcturus trispinosus sp. nov. Figures 8 , 9 , 10 , 11

Material examined.

Holotype. South Korea • 1 ♀ ovigerous (4.5 mm); Jeollanam-do, Yeosu-si, Samsan-myeon, Geomun-ri, Sangbackdo Island; 34°03'4"N, 127°35'13"E; 15 m, 28 Jun. 2017; SCUBA diving; NIBRIV0000813025.

Paratypes. South Korea • 1 ♂ (3.3 mm); Sangbackdo Island; 34°03'15"N, 127°35'00"E; 15 m; 28 Jun. 2017; SCUBA diving • 1 ♀; Sangbackdo Island; 34°03'38"N, 127°35'01"E; 15 m; 28 Jun. 2017; SCUBA diving • 1 ♂, Sosambudo Island; 34°02'23"N, 127°21'43"E; 15 m, 27 Jun. 2017; SCUBA diving; NIBRIV0000880423.

Additional material.

South Korea • 1 ♂, 2 ♀♀; Sinan-gun, Heyksan-myeon, Hondo-ri, Hongdo Island, 34°40'09"N, 125°10'59"E; 10 m; 19 Jun. 2018; SCUBA diving.

Description of holotype female.

Body (Fig. 8A, B ) moderately flattened dorsoventrally, slightly geniculated between pereonites IV and V; length 4.5 mm, 4.5 × longer than wide. Cephalon with three dorsal spines, one pair of lateral spines; anterior margin deeply concave, with small median process; anterolateral lobe expended anteriorly, concave distally; eye large, round, positioned laterally. Pereonites with dorsal spines; pereonite I with one pair of dorsal spines; pereonites II and III similar to each other in length, with one pair of dorsal spines, two pairs of lateral spines; dorsal spines of pereonite III bigger than dorsal spines of pereonite II; pereonite IV widest, ~ 1.5 × longer than pereonites II and III together, with two pairs of small dorsolateral spines, four pairs of dorsal spines, one middorsal spine on posterior margin; posterior dorsal spines larger than other dorsal spines; anterolateral angle expanded laterally; oostegite IV with suture line posteriorly; pereonites V-VII similar to each other in length, with one pair of small dorsal spines, two or three tuberculate elevations. Pleon ~ 1.3 × longer than pereonites V-VII, with two pairs of dorsal spines; anterior spines smaller than posterior spines; pleotelson gradually tapering posteriorly, with three pairs of wings laterally; proximal wing smaller than proceeding wings; apex round.

Antennule (Fig. 9A ) exceeding peduncular article II of antenna, consisting of three peduncular articles and single-articled flagellum; peduncular article I globular, with one projection dorsally and two penicillate setae; article II cylindrical, with five penicillate setae; article III smaller than article II; flagellum with three aesthetascs on anterodistal end and three simple setae on distal end. Antenna (Fig. 9B-D ) almost half of body length, slender, consisting of five peduncular articles and three flagellar articles; peduncular article I small; article II ×longer than article I; article III ×longer than article II, with two short simple setae distally; articles IV and V similar to each other, almost 3 × longer than article III, with numerous minute simple setae along with lateral margin; article IV with one penicillate seta laterally; flagellar article I longer than flagellar articles II and III; articles II and III with one low of spines resembling saw-teeth on ventral margin; article III with one large claw apically.

Left mandible (Fig. 9E ), incisor weakly 4-toothed; lacinia mobilis 3-toothed, with three serrated setae; molar process broad, rough distally. Right mandible (Fig. 9F ), incisor 3-toothed; lacinia mobilis 4-toothed, with two serrated setae; molar process broad, strongly serrated. Maxillule (Fig. 9G ) with fine setae laterally; inner lobe with three trifurcated setae; outer lobe with ten robust setae distally. Maxilla (Fig. 9H ) with fine setae on lateral margin; inner lobe with seven stout circum-plumose setae on subapical region, nine simple setae on apical margin; mesial lobe with four plumose setae apically; outer lobe with three plumose setae distally. Maxilliped (Fig. 9I ), palp article I oval, with three plumose setae; article II square, with four plumose setae; article III cylindrical, with seven plumose setae; article IV oval, shorter than article III, with twelve plumose setae; article V square to globular, with eight plumose setae; endite round, with one coupling hook and four circum-plumose setae laterally, with short bristles apically; epipod globular to oval, with fine setae on distal and mesial margin.

Pereopods I-IV (Fig. 10A-D ) slender, without unguis, consecutively longer. Pereopods V-VII (Fig. 10E-G ) consecutively shorter. Pereopod I (Fig. 10A ), basis longest, with two plumose setae on distal end; ischium 0.3 × as long as basis, with four plumose setae on inferior margin; merus globular to square, with numerous plumose setae inferiorly and two plumose setae on superodistal angle; carpus rectangular, with numerous plumose and serrated setae on inferior margin; propodus elongated oval, subequal in length to carpus, with numerous plumose setae on inferior margin, serrated setae on palmar surface and inferior margin, comb setae on distal end; dactylus small, with two comb setae, two plumose setae distally. Pereopods II-IV (Fig. 10B-D ) similar to each other; basis to propodus with numerous plumose setae on inferior margin; merus to propodus with several simple setae; basis longer than ischium; merus similar to basis in length; carpus and merus subequal in length; propodus slightly shorter than carpus, with several simple setae on distal end; dactylus claw-like. Pereopods V-VII (Fig. 10E-G ) resembling each other; basis with one or three penicillate setae on superior margin; ischium to carpus subequal in length; propodus with two penicillate setae on superior margin; dactylus bi-unguiculate, half of propodus.

Pleopod I (Fig. 11A ), protopod rectangular, with three coupling hooks on inner margin; rami subequal, longer than protopod, with numerous plumose apical setae. Pleopod II (Fig. 11B ) similar to pleopod I; protopod rectangular, with three coupling hooks on inner margin; rami subequal each other, wider than rami of pleopod I, longer than plumose setae, with numerous setae on distal end. Pleopods III-V (Fig. 11C-E ) similar to each other; protopod short; endopod with rounded apex, with 0-2 plumose setae subapically; exopod gradually tapering distal end, almost 1.3 × longer than endopod.

Uropod (Fig. 11F ) elongated oval to rectangular; protopod ~ 3 × longer than wide, with numerous fine setae on border; endopod oval to rectangular, with two plumose setae apically; exopod elongated triangular, with numerous fine setae on border.

Description of paratype male.

Body (Fig. 8D, E ) cylindrical; length 3.3 mm; dorsal spines smaller than those of female. Cephalon (Fig. 8D, E ) with two middorsal spines; anterolateral lobe rounded. Pereonites (Fig. 8D, E ), pereonite I-III without dorsal spines; pereonite IV slender, narrower than that of female, with only one pair of dorsal spines posteriorly. Pleopod I (Fig. 11G ), protopod rectangular, ~ 3.3 × longer than wide, with four coupling hooks medially; rami similar in length, with plumose setae distally; exopod with fine setae subbasally; lateral notch of exopod present, but obscure. Pleopod II (Fig. 8F ), protopod rectangular, with three coupling hooks on inner margin; plumose setae shorter than rami; endopod slightly longer than exopod, with seven plumose setae; exopod ~ 1.6 × longer than protopod, with nine plumose setae; appendix masculine almost 1.8 × longer than endopod, curved outwardly, acute distally.

Distribution.

Southern coast of South Korea.

Habitat.

Sublittoral zone of the rocky substrate.

Etymology.

The composite epithet of the specific name Idarcturus trispinosus is a combination of the Latin tres, meaning three, and spinosus, meaning thorny. This name refers to having three spines on the dorsal surface of the cephalon.

Remarks.

Within the genus, Idarcturus trispinosus sp. nov. is distinguished from I. platysoma , the type species of the genus, by having dorsal spines in both sexes (lacking the dorsal spines in I. platysoma ) and the pleotelson bearing lateral wings (lacking in the latter) ( Barnard 1914).

Idarcturus trispinosus sp. nov. is similar to I. allelomorphus in having dorsal spines, but the former differs by having three dorsal spines on the cephalon (vs. two in the latter) and six pairs of dorsal spines on pereonite IV (vs. one pair in the latter) ( Menzies and Barnard 1959).

Idarcturus trispinosus sp. nov. most resembles I. hedgpethi in having anterolaterally expanded pereonite IV and dorsal spines. However, they could be distinguished by the anterolateral lobe of the cephalon (concave distally in the former vs. truncated in the latter) and the numbers of dorsal spines on the cephalon (three in the former vs. two in the latter), on pereonite IV (six pairs in the former vs. one pair in the latter), and on the pleon (two pairs in the former vs. one pair in the latter) ( Menzies 1951).

Figures

Figure 8. Idarcturus trispinosus sp. nov., holotype, female A habitus, dorsal view B habitus, lateral view C oostegite 4. Paratype, male D habitus, dorsal view E habitus, lateral view F pleopod 2.

Figure 9. Idarcturus trispinosus sp. nov., holotype, female A antennule B antenna C detail of peduncular articles of antenna D flagellum of antenna E left mandible F right mandible G maxillule H maxilla I maxilliped.

Figure 10. Idarcturus trispinosus sp. nov., holotype, female A pereopod 1 B pereopod 2 C pereopod 3 D pereopod 4 E pereopod 5 F pereopod 6 G pereopod 7.

Figure 11. Idarcturus trispinosus sp. nov., holotype, female A pleopod 1 B pleopod 2 C pleopod 3 D pleopod 4 E pleopod 5 F uropod. Paratype, male G pleopod 1.