Limnoria rhombipunctata Yoshino, Watabe & Ohsawa, 2017

Figs 6–10

Limnoria rhombipunctata Yoshino, Watabe & Ohsawa, 2017: 251 –259, figs 1–3.

Material examined. 1 female (NIBRIV0000470351) (Figs 6 A–C & 7A, B), total length 6.8 mm, Goraebawi (Whale rock, Diving point), Oho-ri, Jugwang-myeon, Goseong-gun, Gangwon-do, South Korea, 38°19'39''N, 128°33'45''E, 10 m, SCUBA diving and rinsing Zostera sp., 28 November 2012, coll. T. Park & Y. Eun . 1 female (NIBRIV0000470352), total length 4.5 mm, same location and collectors as above.

Description. Female. Body (Figs 6 A–C & 7A, B) oblong, about 3.4 times as long as greatest width; surface covered with thin setae. Head globular, frontal margin slightly concave. Pereonite 1 longest; 2–5 similar length; 7 shortest. Coxae of pereonites 2–7 large, well visible dorsally. Pleonites 1–4 posterior margins with transverse ridges. Pleonite 5, 0.9 times as long as pleotelson dorsally, with anterior transverse carina and 3 distinctively large nodes, each node surrounded by thin setae. Pleotelson with 1 large median node, followed posteriorly by 2 pairs of carinae, and laterally with 1 more pair of short carinae; posterior margin of pleotelson fringed with stout setae between which are short scale spikes; lateral crests without tubercles. Colour (Fig. 6 A–C) dark yellow in ethanol.

Antennula (Fig. 7 C) with 3 flagellar articles; second articles with about 6 aesthetascs. Antenna (Fig. 7 D) with 4 flagellar articles. Right mandible (Fig. 8 A) palp with 3 articles; incisor beak-like; lacinia mobilis apically bifurcate. Maxillula (Fig. 8 B), outer lobe with 7 apical pectinate spines, lateral margin with simple setae; inner lobe with 3 stout pappose setae. Maxilla (Fig. 8 C) comprises 3 lobes. Maxilliped (Fig. 8 D) palp with 5 articles, distal article smallest; apex of endite with 5 pappose setae and 1 stout seta, inner margin with 1 coupling hook; epipod narrowed distally, triangular, reaching past palp articulation.

Pereopod 1 (Fig. 9 A) ischium without tubercles and ventral comb seta; merus with 5 tubercles, without ventral comb seta; carpus with 2 tubercles, without ventral comb seta; propodus inferodistal margin with 2 comb setae. Pereopod 2 (Fig. 9 B) ischium with 1 tubercle; merus and carpus with 2 tubercles, with 1 ventral comb seta, respectively; Pereopod 3 (Fig. 9 C) ischium with 2 tubercles; merus with 2 tubercles and 1 ventral comb seta; carpus with 2 tubercles, without ventral comb seta. Pereopod 4 (Fig. 9 D) smallest; ischium with 2 tubercles; merus and carpus with 2 tubercles and 1 ventral comb seta, respectively. Pereopod 5 (Fig. 9 E) ischium with 1 tubercle; merus and carpus with 2 tubercles and 1 ventral comb seta, respectively. Pereopod 6 (Fig. 9 F) ischium with 1 tubercle; merus with 2 tubercles and 7 ventral comb setae; carpus with 2 tubercles and 5 ventral comb setae. Pereopod 7 (Fig. 9 G) longest; merus with 15 ventral comb setae; carpus with 10 ventral comb setae. All pereopods with bifid secondary unguis.

Pleopod 1 (Fig. 10 A) peduncle with 3 coupling hooks on inner margin; both rami with numerous plumose setae. Pleopod 2 (Fig. 10 B) peduncle with 2 coupling hooks; both rami with plumose setae up to 0.4 times as long as exopod. Pleopods 3 and 4 (Fig. 10 C, D) peduncle with 2 coupling hooks. Pleopod 5 (Fig. 10 E) peduncle and both rami without seta. Uropod (Fig. 10 F) peduncle with 3 distolateral tubercles; endopod 0.6 times as long as peduncle; exopod short, 0.4 times as long as endopod, claw well developed.

Molecular data. The CO1 sequences obtained from the materials of L. rhombipunctata were deposited in GenBank (accession numbers: KX236457 and KX236458).

Habitat and ecology. Limnoria rhombipunctata, a seagrass borer, was collected from a seagrass-covered sea bottom, 10 m in depth.

Substrate. The rhizome of Phyllospadix iwatensis (type locality, Japan) and Zostera sp. ( South Korea), respectively.

Distribution. Japan (Yoshino et al. 2017), eastern coast of South Korea (this study).

Remarks. To date, Limnoria includes six seagrass-boring species, i.e. L. agrostisa Cookson, 1991, L. mazzellae Cookson & Lorenti, 2001, L. raruslima Cookson, 1991, L. rhombipunctata, L. simulata Menzies, 1957, and L. zinovae (Kussakin, 1963) . Among them, L. rhombipunctata was described based on male specimens collected from the rhizomes of Phyllospadix iwatensis (seagrass) in Japan. Herein, this species is described based on female specimens collected from the rhizomes of Zostera sp. (seagrass) in South Korea. The morphology of the specimens of L. rhombipunctata collected from South Korea agrees well with the illustrations and description of Yoshino et al. (2017); however, we found some sexual dimorphisms in the Korean specimens as follows: (1) maxillipedal epipod with simple setae (vs. maxillipedal epipod without simple setae in the original description); and (2) more numerous setae on pereopods (vs. few setae on pereopods in the illustration of the original description).