Research Article |
Corresponding author: Ko Tomikawa ( tomikawa@hiroshima-u.ac.jp ) Academic editor: Charles Oliver Coleman
© 2018 Ko Tomikawa, Kentaro Hirashima, Atsushi Hirai, Ryu Uchiyama.
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:
Tomikawa K, Hirashima K, Hirai A, Uchiyama R (2018) A new species of Melita from Japan (Crustacea, Amphipoda, Melitidae). ZooKeys 760: 73-88. https://doi.org/10.3897/zookeys.760.24778
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A new brackish-water species of melitid amphipod, Melita choshigawaensis, from the Choshigawa River, Mie Prefecture, Japan, is named and described. Melita choshigawaensis sp. n. is distinguished from the most similar M. shimizui (Uéno, 1940) by having an elongate and weakly arched male uropod 3, and a deep and strongly hooked anterior lobe of the coxa on the female’s pereopod 6. Nucleotide sequences of the mitochondrial cytochrome c oxidase subunit I (COI) of M. choshigawaensis and M. shimizui support divergence at the species level. A key to the Japanese species of Melita is provided.
Brackish water, Choshi River, COI, Mie Prefecture, taxonomy
The amphipod genus Melita Leach, 1814 comprises approximately 80 species worldwide (
During field surveys of aquatic fish and amphipod faunas in the Choshi River, Mie Prefecture, Japan, a new amphipod species was found. Though DNA nucleotide sequence data have been recently successfully used to differentiate morphologically similar amphipod species (
Specimens were collected using a hand net (mouth 25 cm wide, 17 cm high, mesh size 0.1–0.5 mm) from under stones at the mouth of Choshi River, Kihoku, Mie Prefecture (Fig.
Uncorrected p-distances (%) of COI sequences (658 bp) among M. choshigawaensis sp. n. and three populations of M. shimizui (Uéno, 1940). Numbers after localities correspond to locations in Figure
Species | Locality | 1 | 2 | 3 | 4 | |
---|---|---|---|---|---|---|
1 | M. choshigawaensis sp. n. | Choshi River, Mie (1) | 0.0–0.2 | |||
2 | M. shimizui (Uéno, 1940) | Lake Hinuma, Ibaraki (2) | 14.9 | – | ||
3 | Seno River, Hiroshima (3) | 14.9 | 4.4 | – | ||
4 | Ota River, Hiroshima (4) | 14.9 | 4.4 | 0.0 | – |
All appendages were dissected in 80% ethanol and mounted in gum-chloral medium on glass slides using a stereomicroscope (Olympus SZX7). Slides were examined using a light microscope (Nikon Eclipse Ni), with appendages illustrated using a camera lucida. Body length (BL, to the nearest 0.1 mm) was measured from the rostrum tip to the telson base, along the dorsal curvature. Type specimens are deposited at the National Museum of Nature and Science, Tsukuba (
Genomic DNA extraction from body or appendage muscle followed
Holotype: male (BL 5.3 mm,
Male gnathopod 2 propodus with oblique palmar margin; anterior lobe of female pereopod 6 coxa deep and strongly hooked; male uropod 3 outer ramus uni-articulate, weakly arched, its length 7–8 times its width, lacking long setae.
(holotype,
Melita choshigawaensis sp. n., holotype, male, BL 5.3 mm,
Antenna 1 (Fig.
Upper lip (Fig.
Gnathopod 1 (Fig.
Melita choshigawaensis sp. n., holotype, male, BL 5.3 mm,
Pereopod 3 (Fig.
Coxal gills (Fig.
Pleopod 1–3 (Fig.
Melita choshigawaensis sp. n., holotype, male, BL 5.3 mm,
Uropod 1 (Fig.
(paratype,
Melita choshigawaensis sp. n., paratype, female, BL 5.8 mm,
Gnathopod 1 (Fig.
Pereopods 5–7 (Fig.
Uropod 3 (Fig.
16 eggs.
Uropod 3 outer ramus length 2.8 times that of peduncle and 8.2 times outer ramus width (male 6.8 mm,
In total, 658 bp of six nucleotide sequences were determined: paratypes of M. choshigawaensis sp. n. (
Known only from the type locality.
Derived from the name of the type locality.
Melita choshigawaensis is closely related to M. shimizui (Uéno, 1940), originally described from a freshwater pond on Liaodong Peninsula, China (
Melita choshigawaensis is similar to M. laevidorsum Stephensen, 1944 from Korea, and M. myersi Karaman, 1987 from Australia, Fiji, and New Caledonia in that all three have dorsally smooth pleonites, a urosomite 2 with robust setae on their dorsal margins, and an elongate outer ramus of uropod 3 (
Since records of three species, M. coroninii Heller, 1867, M. dentata (Krøyer, 1842), and M. palmata (Montagu, 1804) from Japanese waters are dubious (
1 | Uropod 3, outer ramus 1-articulate | 2 |
‒ | Uropod 3, outer ramus 2-articulate | 9 |
2 | Pleonites 1–3 each with dorsal tooth | M. tuberculata Nagata, 1965 |
‒ | Pleonites 1–3 dorsally smooth | 3 |
3 | Dactylus of pereopods 3 and 4 long, feeble | M. longidactyla Hirayama, 1987 |
‒ | Dactylus of pereopods 3 and 4 short, stout | 4 |
4 | Urosomite 2 with teeth | 5 |
‒ | Urosomite 2 without teeth | 6 |
5 | Female pereopod 6, anterior lobe of coxa shallow, weakly hooked | M. bingoensis Yamato, 1987 |
‒ | Female pereopod 6, anterior lobe of coxa deep, strongly hooked | M. nagatai Yamato, 1987 |
6 | Antenna 2, flagellum strongly setose | M. setiflagella Yamato, 1988 |
‒ | Antenna 2, flagellum weakly setose | 7 |
7 | Antenna 1, accessory flagellum 4-articulate; male gnathopod 2, palm quadrate | M. koreana Stephensen, 1944 |
‒ | Antenna 1, accessory flagellum 2-articulate; male gnathopod 2, palm oblique | 8 |
8 | Male uropod 3 outer ramus weakly arched, more than 7.0 times longer than wide; anterior lobe of coxa of female pereopod 6 as deep as coxa is, strongly hooked | M. choshigawaensis sp. n. |
‒ | Male uropod 3 outer ramus sublinear, about 5 times as long as wide; anterior lobe of coxa of female pereopod 6 depth less than coxal width, weakly hooked | M. shimizui (Uéno, 1940) |
9 | Antenna 2 flagellum strongly setose; uropod 3 outer ramus with long setae | M. quadridentata Yamato, 1990 |
‒ | Antenna 2 flagellum weakly setose; uropod 3 outer ramus without long setae | 10 |
10 | Inferior antennal sinus absent | M. pilopropoda Hirayama, 1987 |
‒ | Inferior antennal sinus present | 11 |
11 | Maxilla 1 palp article 1 with setae; male gnathopod 2 propodus palm oblique | M. hoshinoi Yamato, 1990 |
‒ | Maxilla 1 palp article 1 without setae; male gnathopod 2 propodus palm quadrate | M. rylovae Bulycheva, 1955 |
We thank Mr Itaru Taue and the staff of Camp inn Miyama, Kihoku, Mie Prefecture, for assisting in field surveys. We also thank Steve O’Shea, PhD, from the Edanz Group (www.edanzediting.com/ac), for editing a draft of this manuscript. Thanks are also due to Dr Koraon Wongkamhaeng, Dr Charles Oliver Coleman, and an anonymous reviewer for providing valuable comments on this study. This study was financially supported by JSPS KAKENHI Grant Numbers JP17K15174 and JP17H00820.