Research Article |
Corresponding author: Seong Myeong Yoon ( smyun@chosun.ac.kr ) Academic editor: Charles Oliver Coleman
© 2016 Tae Won Jung, Min-Seop Kim, Ho-Young Soh, 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, Kim M-S, Soh H-Y, Yoon SM (2016) A new species of Eusirus from Jeju Island, Korea (Crustacea, Amphipoda, Eusiridae). ZooKeys 640: 19-35. https://doi.org/10.3897/zookeys.640.10630
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A new eusirid amphipod, Eusirus bulbodigitus sp. n., from Jeju Island, Korea is described with a detailed description and illustrations. Eusirus bulbodigitus sp. n. shows common features with the five known eusirid amphipods E. abyssi Stephensen, 1944, E. columbianus Bousfield & Hendrycks, 1995, E. hirayamae Bousfield & Hendrycks, 1995, E. laticarpus Chevreux, 1906, and E. parvus Pirlot, 1934, such as the mandibular palp article 3 bearing a group of setae laterally. However, this new species is differentiated by the combination of the following characteristics: the eyes are poorly developed, the propodus on pereopod 4 is slightly shorter, the inner margin of dactylus on pereopod 4 is swollen, the length of pereopods 5–7 is moderate, the urosomite 1 has a dorsal protrusion distally, and the telson is shallowly cleft. This is the first record of the genus Eusirus Krøyer, 1845 from Korean waters.
Amphipoda , eusirids, Eusirus bulbodigitus , Korea, new species, taxonomy
Members of the genus Eusirus Krøyer, 1845 share several synapomorphies such as the raptorial gnathopods having a lobate carpus and enlarged propodus, well-developed molars, strong and dentate incisors and dentate left lacinia on the mandible, and a strong maxillipedal palp (
Here, we report a new eusirid species, Eusirus bulbodigitus sp. n. from Jeju Island, Korea, belonging to the family Eusiridae with a detailed description and illustrations. This is the first record of the genus Eusirus from Korean waters.
Sample was collected from subtidal zone using a sledge net (mesh size 300 µm, mouth size 120 × 45 cm). Specimen was initially fixed with 5% formaldehyde-seawater solution and then preserved with 85% ethyl alcohol after sorting in the laboratory. It was stained with lignin pink dyes. Appendages were dissected in Petri dishes filled with glycerol using dissection forceps and a needle under a stereomicroscope (SZH10; Olympus, Tokyo, Japan). Its appendages were mounted on permanent slides using polyvinyl lactophenol solution. Drawings were made under a light microscope (LABOPHOT-2; Nikon, Tokyo) with the aid of a drawing tube. Definition of the term for ‘seta’ and its types follows those of
Jeju Island, South Korea, 33°29'12"N, 126°57'17"E, sublittoral (average depth 33 m).
Holotype: NIBRIV0000332003, adult male, 11.3 mm, collected from the type locality on 30 Nov 2012 by Prof. H-.Y. Soh.
The composite epithet of the specific name, bulbodigitus, is a combination of Latin bulbosus and digitus. This name means ‘swollen dactylus’, referring to the shape of the dactylus on pereopod 4.
Head, lateral cephalic lobe slightly oblique apically; eyes poorly developed. Antenna 1 stout, with peduncular articles 1–3 in length ratio of 4.4:3.8:1.0; peduncular articles 2–3 with 1 robust seta at posterodistal corner subdistally; accessory flagellum uni-articulate. Antenna 2, peduncular article 4 slightly longer than article 5, with calceoli on posterior margin. Maxilla 1, outer plate with 11 dentate setae. Maxilla 2, inner plate broader and larger than outer plate. Left mandible with bi-dentate incisor and 6-dentate lacinia mobilis; right mandible with bi-dentate incisor, lacinia mobilis not split and with 1 row of small dentations apically; palp article 3 with 1 group of 4 serrate setae on lateral margin proximally. Gnathopods stout, “eusiroidean” in form; capus with narrow posterior lobe covered with long serrate setae mediodistally, posterior margin lateral border with acute protrusion at distal corner; propodus wider than long, broad and very deep, with 1 group of defining setae. Pereopod 3 slender, length ratio of merus:carpus:propodus 1.0:0.7:0.9. Pereopod 4, length ratio of merus: carpus:propodus 1.0:0.6:0.7; dactylus with slightly swollen posterior margin. Pereopods 5–7 slender, basis with strong serrations posteriorly. Pleonites 1–2 with acute protrusion dorsodistally; epimeron 3 with 20 serrations posterodistally. Uropod 1, peduncle with 1 enlarged seta at mediodistal corner subdistally; rami lanceolate; outer ramus 0.9 times as long as inner ramus. Uropod 2 0.9 times as long as uropod 1; outer ramus 0.6 times as long as inner ramus. Uropod 3 shortest. Telson shallowly cleft (approximately 1/6 length).
Head (Fig.
Eusirus bulbodigitus sp. n., holotype, male, NIBRIV0000332003, 11.3 mm. Jeju Island, South Korea. A Head B Antenna 1 C Accessory flagellum D Calceoli of flagellum on antenna 1 E Antenna 2 F, G Calceoli of peduncular article 5 and flagellum on antenna 2 H Upper lip I Lower lip J Maxilla 1 K Setae of outer plate on maxilla 1 L Maxilla 2. Scale bars = 0.1 mm (C, D, F, G, K), 0.2 mm (H–J, L), 0.5 mm (A, B, E).
Antenna 1 (Fig.
Antenna 2 (Fig.
Upper lip (Fig.
Lower lip (Fig.
Maxilla 1 (Fig.
Maxilla 2 (Fig.
Left mandible (Fig.
Gnathopod 1 (Fig.
Gnathopod 2 (Fig.
Pereopod 3 (Fig.
Pereopod 4 (Fig.
Pereopod 5 (Fig.
Eusirus bulbodigitus sp. n., holotype, male, NIBRIV0000332003, 11.3 mm. Jeju Island, South Korea. A Pereopod 5 B Posterodistal setae of carpus on pereopod 5 C Dactylus of pereopod 5 D Pereopod 6 E Ischium of pereopod 6 F Distal part of merus on pereopod 6 G Distal part of carpus on pereopod 6 H Dactylus of pereopod 6. Scale bars = 0.1 mm (B, C, E–H), 0.5 mm (A, D).
Pereopod 6 (Fig.
Pereopod 7 (Fig.
Eusirus bulbodigitus sp. n., holotype, male, NIBRIV0000332003, 11.3 mm. Jeju Island, South Korea. A Pereopod 7 B Posterodistal setae of merus on pereopod 7 C Distal part of carpus on pereopod 7 D Dactylus of pereopod 7 E Uropod 1 F Uropod 2 G Uropod 3 H Telson. Scale bars = 0.1 mm (B–D), 0.4 mm (E–H), 0.5 mm (A).
Pleon (Fig.
Uropod 1 (Fig.
Uropod 2 (Fig.
Uropod 3 (Fig.
Telson (Fig.
Eusirus bulbodigitus sp. n. shares the characteristic of a mandibular palp bearing a group of setae laterally on the 3rd article with five known species: E. abyssi Stephensen, 1944; E. columbianus Bousfield & Hendrycks, 1995; E. hirayamae Bousfield & Hendrycks, 1995; E. laticarpus Chevreux, 1906; and E. parvus Pirlot, 1934 (
1 | Mandibular palp article 3 with 1 group of lateral setae proximally | 2 |
– | Mandibular palp article 3 without lateral setae proximally | 4 |
2 | Eyes developed; pereopod 4, articles moderate (not reduced than those of pereopod 3) | 3 |
– | Eyes poorly developed; pereopod 4, articles slightly reduced than those of pereopod 3 | E. bulbodigitus sp. n. |
3 | Coxa 6, posterior lobe not expanded posterodistally; coxa 7 bilobed; uropod 1, peduncle with developed inter-ramal process | E. columbianus Bousfield & Hendrycks, 1995 |
– | Coxa 6, posterior lobe expanded posterodistally; coxa 7 unilobed; uropod 1, peduncle without developed inter-ramal process | E. parvus Pirlot, 1934 |
4 | Pleonal epimeron 3 strongly serrate along posterior margin; telson cleft deeply | 5 |
– | Pleonal epimeron 3 not serrate or weakly serrate along posterior margin; telson not deeply cleft (slightly notched apically) | 6 |
5 | Coxa 1 moderately expanded backwards; uropod 3, inner ramus slightly shorter than outer ramus; telson cleft apically approx. 1/2 length | E. cuspidatus Krøyer, 1845 |
– | Coxa 1 strongly expanded backwards; uropod 3, rami subequal in length; telson cleft apically approx. 1/3 length | E. hirayamae Bousfield & Hendrycks, 1995 |
6 | Antenna 2, peduncular articles slender; pereopod 5, basis broadly expanded posteriorly; pereopod 7, basis narrowly expanded posteriorly; telson elongate | E. bathybius Schellenberg, 1955 |
– | Antenna 2, peduncular articles stout; pereopod 5, basis weakly expanded posteriorly; pereopod 7, basis convex posteroproximally; telson triangular | E. fragilis Birstein & Vinogradov, 1960 |
We thank the captain and the crew of the R/V Cheong Gyeong Ho of Chonnam National University for their assistance in sampling. 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 (NIBR NO. 2014-01-001)’, the research funds from Chosun University (2016) and partly supported by the National Marine Biodiversity Institute of Korea as a part of the ‘Molecular ecology of suborder Gammaridea populations in Korea (2016M01400)’.