Research Article |
Corresponding author: Seong Myeong Yoon ( smyun@chosun.ac.kr ) Academic editor: Danilo Harms
© 2017 Tae Won Jung, Charles Oliver Coleman, Seong Myeong Yoon.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Jung TW, Coleman CO, Yoon SM (2017) Pseudorchomene boreoplebs, a new lysianassid amphipod from Korean waters (Crustacea, Amphipoda, Lysianassoidea). Zoosystematics and Evolution 93(2): 343-352. https://doi.org/10.3897/zse.93.20482
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Until now, the genus Pseudorchomene Schellenberg, 1926 has been recorded exclusively in Antarctic or sub-Antarctic regions. Pseudorchomene boreoplebs sp. n., described from Korean waters, is the first record from the Northern Hemisphere as well as from temperate regions. This new species is very similar to Pseudorchomene plebs (Hurley, 1965), but can be readily distinguished by its wider basis of gnathopod 1, elongate carpus and angulate anterodistal corner of the propodus on gnathopod 2, having slender setae only on the posterior margin of the carpus on pereopod 5, and lacking posterior lobations of the carpus on pereopods 5–7.
Pseudorchomene boreoplebs , amphipod, Korea, lysianassid, new species, taxonomy
Previously, members of the genus Pseudorchomene Schellenberg, 1926 were considered to belong to the complicated ‘Orchomene complex’ (
In this study, the genus Pseudorchomene is recorded for the first time from the Northern Hemisphere, in Korean waters, with the description of Pseudorchomene boreoplebs sp. n. A key to all known species of the genus Pseudorchomene is also provided.
The collected specimens of lysianassids were initially fixed in 80% ethyl alcohol in the field and then preserved in 95% ethyl alcohol after sorting in the laboratory. Specimens were stained with lignin pink before dissection. Their appendages were dissected in petri dishes or excavated microscopic slides filled with mixed solution of glycerol-ethanol using dissecting forceps and needles under a stereomicroscope (Leica M205), and mounted onto temporary slides using glycerol. To prepare illustrations, pencil drawings were made under a light microscope (Leica DMLB) with the aid of a drawing tube. These were then scanned, digitally inked, and arranged on digital plates using the methods described by
Korean Name: Gae-gin-pal-yeop-sae-u-sok, new
Near Daejin Port, Daejin-ri Hyeonnae-myeon Goseong-gun Gangwon-do South Korea. The specimens were collected from fishery nets of this port. According to the statements of fishermen, these nets were brought out within a 5 km radius from Daejin Port and the nets were deployed in about 1–2 km depth (The precise coordinates were uncertain).
Holotype: female, 27.1 mm (NIBRIV0000806535), paratypes: two males, 15.5–18.0 mm and two females, 15.9–23.5 mm (NIBRIV0000807159); collected from fishery nets in Daejin Port, 11 Mar 2016, by TW Jung.
The composite epithet of the specific name, boreoplebs is a combination of the Latin borealis and the specific name of Pseudorchomene plebs (Hurley, 1965). This name refers to a ‘similar species to P. plebs living in the northern region’.
Eyes red or brown in life. Antenna 2 not reduced in both sexes. Gnathopod 1 stocky; basis largely expanded, 2.1 × as long as wide; palm transverse, convex, margin serrated. Gnathopod 2 carpus 0.7 × as long as basis, 3.5 × as long as wide; propodus 0.4 × as long as carpus, weakly angulated anterodistally. Pereopod 5 coxa wider than long; merus posterior lobe well developed, lined with slender setae only (without robust setae). Uropod 3 inner ramus not reaching distal end of proximal article of outer ramus.
Head (Fig.
Antenna 1 (Fig.
Antenna 2 (Fig.
Upper lip (Fig.
Mandible (Fig.
Maxilla 1 (Fig.
Maxilla 2 (Fig.
Maxilliped (Fig.
Pereon.Gnathopod 1 (Fig.
Gnathopod 2 (Fig.
Pereopod 3 (Fig.
Pereopod 4 (Fig.
Pereopod 5 (Fig.
Pereopod 6 (Fig.
Pereopod 7 (Fig.
Pleon.Epimeron 1 subquadrate, somewhat produced anteroventrally, ventral margin straight, posterior margin convex, with an oblique ridge on surface. Epimeron 2 larger than epimeron 1 anteroventral corner rounded, weakly produced, ventral margin concave, posteroventral corner subquadrate, with an oblique ridge on surface. Epimeron 3 largest, somewhat expanded antero- and posteroventrally, posterior margin rounded. Urosomite 1 with deep dorsal depression and mid-dorsal carina (Fig.
Uropod 1 (Fig.
Uropod 2 (Fig.
Uropod 3 (Fig.
Telson (Fig.
Body length between 15.5–18.0 mm, smaller than those of females (15.9–23.5 mm). Not sexually dimorphic in both sexes.
Among five valid species of the genus Pseudorchomene, P. coatsi, P. debroyeri and P. lophorachis are similar to each other in sharing a characteristic gnathopod 1: the convex anterior margin of the basis and the elongate and extremely slender articles from ischium to dactylus (
1 | Gnathopod 1 basis anterior margin convex; other articles slender and elongate | 2 |
– | Gnathopod 1 short, stocky; basis largely expanded, anterior margin straight | 4 |
2 | Somites of pereon and pleosome with small posterior humps | Pseudorchomene lophorachis d’Udekem d’Acoz & Haverman, 2012 |
– | Somites of pereon and pleosome without small posterior humps | 3 |
3 | Gnathopod 1 palm oblique. Gnathopod 2 carpus 2.3 × as long as wide. Pereopod 7 carpus anterior margin setose moderately, posterior margin with posterodistal setae only | Pseudorchomene coatsi (Chilton, 1912) |
– | Gnathopod 1 palm transverse. Gnathopod 2 carpus 3.0 × as long as wide. Pereopod 7 carpus anterior margin setose densely, posterior margin and posterodistal corner with setae | Pseudorchomene debroyeri d’Udekem d’Acoz & Haverman, 2012 |
4 | Eye deep black in life. Pereopod 5 merus of 1.2 × as long as wide, posterior margin with robust setae only. Uropod 3 inner ramus reaching the base of article 2 of outer ramus | Pseudorchomene rossi (Walker, 1903) |
– | Eye red or dark brown in life. Pereopod 5 merus of 1.5 × as long as wide, posterior margin with slender and robust setae or slender setae only. Uropod 3 inner ramus not reaching the base of article 2 of outer ramus | 5 |
5 | Gnathopod 2 carpus 0.5 × as long as basis, 2.6 × as long as wide; propodus convex anteriorly (not angulate anterodistally). Pereopod 5 merus with slender and robust setae | Pseudorchomene plebs (Hurley, 1965) |
– | Gnathopod 2 carpus 0.7 × as long as basis, 3.6 × as long as wide; propodus weakly angulate anterodistally. Pereopod 5 merus with slender setae only | Pseudorchomene boreoplebs sp. n. |
This study was supported by the National Institute of Biological Resources of Korea as a part of the ‘Survey of indigenous biological resources of Korea (