Tachaea koreaensis, 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 : 17-18

Tachaea koreaensis sp. n. Figures 5, 6, 7

Material examined.

Holotype: non-ovigerous female (4.8 mm, NIBRIV0000554215); Buheungji reservoir, Yeongcheon-si, Gyeongsangbuk-do, South Korea; 35°55'19"N, 128°59'14"E; 18 April 2013; approximately 2 m; coll. K.-S. Sim; ectoparasites of Macrobrachium nipponense . Paratype: non-ovigerous female (4.3 mm, NIBRIV0000754063); Wolga reservoir, Wolga-ri, Gunnae-myeon, Jindo-gun, Jeollanam-do, South Korea; 34°29'36"N, 126°17'35"E; 23 September 2016; 1.4 m; using a landing net; coll. D.-H. Ahn, C. W. Lee, H.-M. Yang and J.-H. Song; ectoparasites of Palaemon paucidens .

Etymology.

The specific name ' koreaensis ' is derived from the name of the nation from which the specimens were collected.

Diagnosis.

Pereopods 1-3 propodus expanded with serrations on inferior margins. Pereopods 4-7 propodus with serrations on inferodistal margins. Mandible incisor with one cusp. Maxilla apical lobe with one seta. Maxillipedal palp with four articles. Pleotelson with ten robust setae on posterior margin.

Description

(non-ovigerous female, holotype).Body (Figure 5A) 2.2 times as long as greatest width. Colour yellowish; chromatophores on all somites, including both antennae and uropods. Cephalon (Figure 5A) 2.6 times wider than medial length. Eyes (Figure 5A) with 26-28 ommatidia. Pereonite 1 (Figure 5A) longest, 1.7 times as long as pereonite 2 and 4, 1.4 times as long as pereonite 3, 1.8 times as long as pereonite 5, 2.1 times as long as pereonite 6, 2.8 times as long as pereonite 7.

Frontal lamina (Figure 5B) elongate, narrow; clypeus short and broad.

Antennula (Figure 5C) peduncle article 1 triangular, 1.1 times as long as wide, with four setae and two penicillate setae; article 2 0.7 times as long as article 1, with two setae and one penicillate seta; article 3 minute, 0.2 times as long as article 2, with three setae distally; flagellum with seven articles, articles 3-6 with 2 aesthetascs, articles 6 and 7 minute. Antenna (Figure 5D) peduncle article 1 0.8 times as long as wide, with one seta; article 2 shortest, with two setae; article 3 2.0 times as long as article 2, with two setae; article 4 with two setae; article 5 with six setae and two penicillate setae; articles 4 and 5 similar length; flagellum with 12 articles, each articles with six setae.

Mandible (Figure 5E) palp article 2 with four serrate setae and two setae; article 3 with seven short serrate setae, three serrate setae. Lacinia mobilis and molar process absent; incisor monocuspid. Maxillula (Figure 5G) lateral lobe forming single large curved spine. Maxilla (Figure 5H) short, apical lobe with one seta. Maxilliped (Figure 5F) without endite; palp with four articles, narrow, 4.4 times as long as wide.

Pereopods 1-3 (Figure 6 A–C) similar, propodus inferior margins expanded with serrations. Pereopod 1 basis 2.7 times as long as greatest width, superior margin with three setae, inferodistal margin with one seta; ischium 0.6 times as long as basis, 1.8 times as long as wide, superior margin with two setae, inferior margin with two setae; merus 0.6 times as long as ischium, 0.8 times as long as wide, superodistal margin with two setae and one robust setae, inferodistal margin with three robust setae, inferior margin with one seta; carpus shortest, 0.4 times as long as merus, 0.3 times as long as wide, superodistal margin without setae, inferodistal margin with five robust setae; propodus 1.2 times as long as ischium, 1.7 times as long as wide, superior margin with one seta and one penicillate seta, inferior margin with three robust setae, one comb seta and one seta; dactylus 0.5 times as long as propodus. Pereopods 4-7 (Figure 6 D–G) similar, propodus inferodistal margins with serrations. Pereopods 4 and 5 carpi with three comb setae; pereopod 6 carpus with four comb setae, propodus with three comb setae; pereopod 7 carpus with seven comb setae, propodus with five comb setae.

Pleopods 1-5 (Figure 7 A–E) similar; exopod broader, longer than endopod, with plumose setae; endopod naked. Pleopods 1-4 peduncle wider than long, with 5-6 coupling spines and 1-2 plumose setae. Pleopod 5 peduncle without coupling spines. Uropod (Figure 7F) rami reaching pleotelson; peduncle distal margin with three setae, proximal margin with two setae, lateral margin with one seta; endopod (Figures 5A, 7G) not surpassing pleotelson, 2.1 times as long as greatest width, lateral margin with one robust setae and plumose setae, mesial margin truncate, with seven robust setae and plumose setae; exopod (Figures 5A, 7H) not extending to end of endopod, 3.1 times as long as greatest width, lateral margin with four robust setae and plumose setae; mesiodistal margin with three robust setae and plumose setae. Pleotelson (Figure 7I) 0.8 times as long as anterior width; posterior margin rounded, with ten robust setae and numerous plumose setae.

Remarks.

Tachaea koreaensis sp. n. is distinguished from other known species of Tachaea by the following combination of characters: 1) the inferior margins of the propodus of pereopods 1-3 is expanded with serrations, 2) the inferodistal margins of the propodus of pereopods 4-7 with serrations, 3) the apical lobe of the maxilla with one seta, and 4) the posterior margin of the pleotelson with ten robust setae.

Tachaea koreaensis sp. n. is most similar to T. spongillicola from India, but it can be distinguished from the latter by the following characters: the ratio of pereonite 1 to pereonite 2, the number of cusps on the mandible, the presence or absence of setae on the apical lobe of the maxilla, and the number of robust setae on the posterior margin of the pleotelson. In T. spongillicola , the pereonite 1 is as long as the pereonite 2, the incisor of the mandible with two cusps, the apical lobe of the maxilla without seta, and the posterior margin of the pleotelson with eight robust setae. In comparison, in the new species, the pereonite 1 is 1.7 times as long as the pereonite 2, the incisor of the mandible with one cusp, the apical lobe of the maxilla with one seta, and the posterior margin of the pleotelson with ten robust setae.

Distribution.

Jeollanam-do and Gyeongsangbuk-do (South Korea).