Arcturina serrulatus, Song, Ji-Hun, Park, Taeseo, Kim, Won & Min, Gi-Sik, 2017

Song, Ji-Hun, Park, Taeseo, Kim, Won & Min, Gi-Sik, 2017, Arcturina serrulatus sp. nov. and a new record of Limnoria rhombipunctata (Crustacea: Malacostraca: Isopoda) from South Korea, Zootaxa 4286 (3), pp. 411-424 : 412-417

Arcturina serrulatus sp. nov.

Figs 1–5

Material examined. Holotype (NIBRIV0000437271): Female, here designated, total length 4.5 mm, coast of Boryung-si, Chungcheongnam-do, South Korea, 36°23'36''N, 126°26'36''E, 10 m, van Veen grab, 20 February 2015, coll. S. Ju.

Paratype (NIBRIV0000437272): Female, total length 4.3 mm; same location and collector as the holotype.

Description. Female holotype. Body ( Figs 1 A, B & 2A, B) about 3.1 times as long as greatest width, with 2 strong dorsal ridges along whole body (from head to pleotelson), ridges almost parallel; head and pereonites 1–4 together forming diamond-shaped dorsally, with lateral ridges. Pereonite 4 almost straight in lateral view, 0.6 times as long as wide, widest at anterior one-third. Pereonites 5–7 and pleonites 1, 2 with lateral ridges. Eyes ( Fig. 2 A, B) large, bulging laterally. Pleotelson ( Fig. 2 A, B) 2.0 times as long as wide, apex rounded, without excavation, with lateral ridges. Colour ( Fig. 1 A, B) dark-brownish in ethanol.

Antennula ( Fig. 2 C) comprises 3 peduncular articles and one flagellum; peduncular article 2 and 3 similar length; flagellum with one aesthetasc and 2 simple setae. Antenna ( Fig. 2 D) 0.6 times as long as body; peduncular article 3 inferior margin with 4 pairs of simple setae, articles 4 and 5 longer than articles 1–3, with 10 pairs of simple setae; flagellum ( Fig. 2 E) with 3 articles, distal two articles with row of spines resembling saw-teeth (see Bamber 2008).

Left Mandible ( Fig. 3 A), incisor with 5 spine-row; lacinia mobilis stout, with 1 large serrate spine-like seta and 2 spine-like setae; molar process truncate, bearing many short setae. Maxillula ( Fig. 3 B), outer lobe with 7 apical pectinate spines, lateral margin with simple setae; inner lobe with 3 stout pappose setae. Maxilla ( Fig. 3 C) comprises 3 lobes; mesial lobe apex with 5 pappose setae and 4 elongate plumose setae; middle lobe and outer lobe apex with 2 plumose setae. Maxilliped ( Fig. 3 D), palp with 5 articles, article 1 smallest; article 2 with 5 long setae and short setae; article 3 with 5 long setae and short marginal setae; article 4 with 4 long setae; last article with 3 long setae; endite apex with 3 pappose setae, inner margin with 1 coupling hook; epipod large, rectangular, with short setae.

Pereopod 1 ( Fig. 4 A) robust, surface covered with short setae; basis 2.5 times as long as wide, inferior margin with short setae and 1 long seta; ischium 2.0 times as long as wide, inferior margin with short setae and 4 long setae; merus trapezoid, wider than long, 0.8 times as long as wide, inferior margin with short setae and 2 long setae; carpus rectangular, 2.1 times as long as wide, inferior margin with short setae and 4 pappose setae; propodus 1.8 times as long as wide, inferior margin with short setae and 1 pappose seta and 4 setae, distal margin with 8 setae, median surface with row of 8 setae; dactylus, 3.5 times as long as wide, with well-developed long unguis.

Pereopod 2 ( Fig. 4 B) longer than pereopod 1, surface and whole superior margin with short setae; basis 1.9 times as long as wide; ischium 1.2 times as long as wide, inferior margin with short setae and 1 long seta; merus trapezoid, length similar to width, inferior margin with short setae and 2 long setae; carpus trapezoid, length similar to width, inferior margin with short setae and 4 long setae; propodus 1.2 times as long as wide, inferior margin with short setae and 3 long setae; dactylus 3.0 times as long as wide, distal margin with 2 plumose setae and 3 long setae, without unguis.

Pereopod 3 ( Fig. 4 C) similar to pereopod 2; basis 2.3 times as long as wide; ischium 2.1 times as long as wide, inferior margin with short setae and 5 long setae; merus length similar to width, inferior margin with short setae and 3 long setae; carpus 1.2 times as long as wide, inferior margin with short setae and 3 long setae; propodus 1.4 times as long as wide, inferior margin with short setae and 1 long seta; dactylus 3.0 times as long as wide, distal margin with 2 plumose setae and 1 long seta.

Pereopod 4 ( Fig. 4 D) small, shortest; basis length similar to width; ischium 2.4 times as long as wide; merus 1.8 times as long as wide, inferior margin with short setae and 1 long seta, superior margin with short setae and 1 long seta; carpus 1.2 times as long as wide, inferior margin with short setae and 1 long seta, superior margin with short setae and 1 long seta; propodus 2.0 times as long as wide; dactylus 2.0 times as long as wide, distal margin with 2 plumose setae and 1 long seta.

Pereopods 5–7 ( Fig. 4 E–G) progressively smaller; basis and ischium with serrate margins; carpus inferodistal margin with serrate process. Pereopod 5, basis 3.4 times as long as wide, inferior margin with 3 simple setae, distal margin with 3 simple setae; ischium 2.7 times as long as wide, inferior and superior margin with 2 simple setae, respectively; merus 1.7 times as long as wide, inferodistal margin and superodistal margin with 2 simple setae, respectively; carpus 3.4 times as long as wide, inferodistal margin with serrate process, superior margin with 2 simple setae; propodus 4.4 times as long as wide, inferior margin with 2 simple setae, inferodistal margin with 1 simple seta; dactylus 3.8 times as long as wide, inferior margin with 5 simple setae, distal margin with 5 simple setae, with well-developed unguis. Pereopods 6 and 7 similar to pereopod 5.

Pleopod 1 ( Fig. 5 A) peduncle with 3 retinaculae on inner margin; outer margin with short setae; both rami distal margin truncate, with numerous plumose setae. Pleopod 2 ( Fig. 5 B) peduncle with 4 retinaculae on inner margin; both rami with distal margin truncate, with numerous plumose setae. Pleopod 3 ( Fig. 5 C) exopod with 2 plumose setae; endopod naked. Pleopod 4 ( Fig. 5 D) exopod with 1 plumose seta; endopod naked. Pleopod 5 ( Fig. 5 E) both rami without setae. Uropod ( Fig. 5 F, G) inner margin with short setae; peduncle 4.0 times as long as wide, outer margin with 2 plumose setae and 2 simple setae distally, distal margin with 1 finely plumose seta and 1 simple seta; endopod short, 0.09 times as long as peduncle, with marginal short setae.

Molecular data. The CO1 sequence obtained from the holotype of A. serrulatus sp. nov. was deposited in GenBank (accession number: KX078772 ).

Habitat. This species was collected from 10 m depth in organic-rich muddy sand.

Distribution. Western coast of South Korea (known only from the type locality).

Etymology. From the Latin words “ serrula ” (serrated) and “ marginatus ”, alluding to the serrated margin of the basis and ischium of pereopods 5–7 in this species.

Remarks. Arcturina serrulatus sp. nov. is distinguished from the other Arcturina species by the following combination of characters: (1) presence of two strong dorsal ridges and lateral ridges on the whole body; (2) pereonite 4 almost straight in lateral view; (3) presence of serrations on the basis and ischium of pereopods 5–7, and a serrate process on the inferodistal margin of the carpus; (4) pleotelson apex with rounded margin, without notch; and (5) presence of a single aesthetasc on the antennular flagellum. This species is most similar to A. triangularis Barnard, 1957 . However, it can be distinguished by the following characters: (1) dorsal ridges extending to the head that do not converging on pereonite 3 and anterior part of pereonite 4 (vs. dorsal ridges extending to the head that converging on pereonite 3 and anterior part of pereonite 4 in A. triangularis ); (2) head with small medial projection (vs. head without medial projection in A. triangularis ); and (3) presence of serrations on pereopods 5–7 (vs. absence of serrations in A. triangularis ). Arcturina serrulatus sp. nov. is also distinguished from two Asian ( Hong Kong and Japan) species of Arcturina as follows: from A. psittacus Bamber, 2008 ( Hong Kong) in having dorsal ridges on pereonites 5–7 and serrations on the basis and ischium of pereopods 5–7; and from A. plumbiformis Nunomura, 2008 ( Japan) by the absence of lateral projection on pereonite 5.

Figures

FIGURE 1. Arcturina serrulatus sp. nov., female holotype. A, body, lateral view; B, body, dorsal view. Scale bars = 1 mm (A, B).

FIGURE 2. Arcturina serrulatus sp. nov., female holotype. A, body, lateral view; B, body, dorsal view; C, antennula; D, antenna; E, antenna, flagellum. Scale bars = 1 mm (A, B), 0.1 mm (C, E), 0.2 mm (D).

FIGURE 3. Arcturina serrulatus sp. nov., female holotype. A, left mandible; B, maxillula; C, maxilla; D, maxilliped. Scale bars = 0.05 mm (A – D).

FIGURE 4. Arcturina serrulatus sp. nov., female holotype. A, pereopod 1; B, pereopod 2; C, pereopod 3; D, pereopod 4; E, pereopod 5; F, pereopod 6; G, pereopod 7. Scale bars = 0.1 mm (A – D), 0.2 mm (E – G).

FIGURE 5. Arcturina serrulatus sp. nov., female holotype. A, pleopod 1; B, pleopod 2; C, pleopod 3; D, pleopod 4; E, pleopod 5; F, uropod; G, uropod, endopod. Scale bars = 0.2 mm (A – F), 0.1 mm (G).