Gnathia koreana, Song, Ji-Hun & Min, Gi-Sik, 2018

Song, Ji-Hun & Min, Gi-Sik, 2018, First records of Gnathia Leach, 1814 and Tachaea Schioedte & Meinert, 1879 from South Korea, with descriptions of two new species (Isopoda, Cymothoida, Cymothooidea), ZooKeys 787, pp. 17-35 : 17

Gnathia koreana sp. n. Figures 1, 2, 3, 4

Material examined.

Holotype: adult male (4.6 mm, NIBRIV0000554213); Yeogaekseon terminal, Geomundo Island, Yeosu-si, Jeollanam-do, South Korea; 34°01'37"N, 127°18'27"E; 31 May 2014; approximately 10 m; coll. J.-H. Song. Paratype: adult male (4.3 mm, NIBRIV0000554214), same sample as holotype.

Etymology.

The specific name ‘koreana’ is derived from the name of the nation from which the specimens were collected.

Diagnosis.

Pereon dorsal surface smooth, sparsely setose, without tubercles. Cephalon dorsal surface sparsely setose with several granules medially. Paraocular ornamentation strongly developed, forming a ridge, without tubercles. Mediofrontal process strong and bifid. Superior frontolateral process shorter than mediofrontal process, rounded, and serrated. Mandible without pseudoblade and internal lobe.

Description

(adult male, holotype).Body (Figures 1A, B, 2A) 3.2 times as long as greatest width; dorsal surfaces smooth, sparsely setose. Cephalon (Figure 1C) rectangular, 0.7 times as long as wide, lateral margins slightly convex and smooth; dorsal surface sparsely setose with several granules medially; dorsal sulcus wide, deep; paraocular ornamentation (Figure 1E, F) strongly developed, forming ridge, without tubercles; posteromedian tubercle present. Eyes (Figure 2A) 0.3 times as long as cephalon. Supraocular lobe (Figure 2A) weak, with blunt apex; accessory supraocular lobe not pronounced. Mediofrontal process (Figure 2B) elongated, bifid. Superior frontolateral process (Figure 2B) shorter than mediofrontal process, serrated. Inferior frontolateral process absent. Pereonites 1-7 (Figure 2A) without tubercles on dorsal surface, lateral margins smooth; pereonite 1 not fused dorsally with cephalon, dorsolateral margins fully obscured by cephalon; pereonite 2 wider than pereonite 1; pereonite 4 with anterior constriction; areae laterales present on pereonite 5; pereonite 6 with lobi laterales; pereonite 7 narrow, overlapping pleon; lobuii weak, globular. Pleonites 1-5 (Figure 2A), epimera not visible dorsally. Pleotelson (Figure 4F) 0.9 times as long as anterior width, lateral margins smooth, anterolateral margins not concave, posterolateral margins weakly concave; mid-dorsal surface with two sub-median setae, posterolateral margins with two submarginal setae, apex with two setae.

Antennula (Figure 2C) peduncle article 2 0.6 times as long as article 1; article 3 1.7 times as long as article 2; flagellum with five articles. Antenna (Figure 2D) peduncle article 4 3.0 times as long as wide, 1.2 times as long as article 3, with two penicillate setae; flagellum with seven articles.

Mandible (Figures 1C, D, 2E) 0.5 times as long as width of cephalon, curved upward; mandibular seta present; carina present, unornamented; incisor elevated, distally rounded; dentate blade with five weak processes; pseudoblade absent; internal lobe absent; dorsal lobe absent; basal neck short; erisma absent; lamina dentate absent. Maxilliped (Figure 2F) article 1 lateral margin with continuous marginal setae; article 2 lateral margin with three plumose setae; article 3 lateral margin with seven plumose setae; article 4 lateral margin with four plumose setae; article 5 with seven plumose setae; endite extending to distal margin of article 2; without coupling setae. Pylopod (Figure 2G) with three articles; article 1 1.4 times as long as wide, without distolateral lobe, with three areolae; posterior and lateral margins forming rounded curve; lateral margin with 30 plumose setae; mesial margin with continuous setae, distal margin with 5-6 setae; article 2 1.3 times as long as wide; article 3 minute.

Pereopods 2-6 (Figure 3 A–E) without long plumose setae; basis superior margin with 2-3 penicillate setae; dactylus superodistal margin with one penicillate seta. Pereopod 2 basis 2.4 times as long as greatest width, superior margin with two setae, inferior margin with three setae; ischium 0.7 times as long as basis, 2.4 times as long as wide, superior margin with three setae, inferior margin with four setae and four tubercles; merus 0.6 times as long as ischium, 1.8 times as long as wide, superodistal margin with one seta, inferior margin with one seta and four tubercles; carpus as long as merus, 2.1 times as long as wide, superodistal margin with one seta, inferior margin with three setae and three tubercles; propodus 0.8 times as long as ischium, 3.5 times as long as wide, superior margin with three setae, inferior margin with two robust setae; dactylus 0.3 times as long as propodus. Pereopods 3-6 similar, but basis superior margin with 3-6 tubercles.

Pleopods 1-5 (Figure 4 A–E) similar. Pleopod 2 exopod 2.3 times as long as wide, with 8 plumose setae; endopod 2.5 times as long as wide, with seven plumose setae; appendix masculina with parallel margins, 0.6 times as long as endopod, distally rounded. Uropod (Figure 4F) rami extending beyond pleotelson, apices rounded; peduncle with two setae; endopod 2.6 times as long as greatest width, lateral margin with three setae, mesial margin with eight plumose setae, dorsally with one penicillate seta; exopod not extending to end of endopod, 4.0 times as long as greatest width, lateral margin with three setae; mesiodistal margin with three plumose setae.

Habitat.

This species was collected at approximately 10 m depth corresponding to a sedimentary bottom of muddy sand.

Remarks.

Gnathia koreana sp. n. is distinguished from other known species of Gnathia by the following characters: 1) the dorsal surface of the pereon without tubercles, 2) the paraocular ornamentation is strongly developed, forming a ridge, without tubercles, 3) the mediofrontal process is strong and bifid, 4) the superior frontolateral process is shorter than the mediofrontal process, rounded, and serrated, and 5) the mandible without internal lobe.

Gnathia koreana sp. n. is most similar to G. excavata from Japan in terms of the following characters: the body is smooth, the mediofrontal process is bifid, and the mandible without internal lobe. However, the new species is distinguished from G. excavata by the shape of the paraocular ornamentation and superior frontolateral process. In G. excavata , the paraocular ornamentation with three indistinct tubercles and the superior frontolateral process is acute and not serrated. In comparison, in the new species, the paraocular ornamentation with distinct unornamented ridge and the superior frontolateral process is rounded and serrated.

Distribution.

Only known from the type locality.