Research Article |
Corresponding author: Ko Tomikawa ( tomikawa@hiroshima-u.ac.jp ) Academic editor: Rachael Peart
© 2022 Takanobu Arai, Yujiro Ohno, Ko Tomikawa.
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:
Arai T, Ohno Y, Tomikawa K (2022) A new species of the genus Podocerus from the Seto Inland Sea, Japan (Crustacea, Amphipoda, Podoceridae). ZooKeys 1128: 99-109. https://doi.org/10.3897/zookeys.1128.91155
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A new podocerid amphipod, Podocerus setouchiensis sp. nov., is described from the Etajima Island, the Seto Inland Sea, Japan. This new species differs from its congeners by the dorsal carination of pereonites and pleonites, and form of the antenna 1, gnathopods 1 and 2, uropods 1 and 2, and telson. Nucleotide sequence data of the mitochondrial cytochrome c subunit I (COI) from a paratype of Podocerus setouchiensis sp. nov. is provided for future molecular systematic studies.
COI, intertidal, podocerid, Podocerus setouchiensis, systematics
Podocerus Leach, 1814, is an amphipod crustacean genus belonging to the family Podoceridae Leach, 1814 and is cosmopolitan in world seas (
The Seto Inland Sea is the largest inland sea in Japan, surrounded by the three of four largest islands in Japan (excluding Okinawa), Honshu, Shikoku, and Kyushu, with more than 700 islands and a rich marine ecosystem. More than 90 species of amphipods have been reported from the Seto Inland Sea (
Specimens were collected using a hand net and fixed in 99% ethanol on-site (Fig.
All appendages were dissected using insect pins 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. Bodies were dehydrated through a graded ethanol series, and dried using hexamethyldisilazane (HMDS) (
Genomic DNA extraction from body or appendage muscle followed
Infraorder Corophiida Leach, 1814
Superfamily Caprelloidea Leach, 1814
Family Podoceridae Leach, 1814
Holotype
:
Body weakly rugose; pereonites 6–7 and pleonites 1–2 with dorsal carina. Head dorsally smooth. Antenna 1 accessory flagellum 1-articulate. Antenna 2 flagellar article 1 elongate. Uropod 3 rami with setae. Telson shorter than wide, with 2 long robust setae apically, lower margin with short lateral setae.
(male, holotype,
Antenna 1 (Fig.
Podocerus setouchiensis sp. nov., holotype male,
Upper lip (Fig.
Gnathopod 1 (Fig.
Pereopods 3 and 4 (Fig.
Podocerus setouchiensis sp. nov., holotype male,
Pleopods 1–3 (Fig.
Uropod 1 (Fig.
Telson (Fig.
Female (paratype,
Gnathopod 1 (Fig.
The specific name is derived from the Seto Inland Sea, where this new species is distributed.
A sequence of COI (GenBank accession number LC719250; 658 bp) was determined from the paratype female (
Known from Hiroshima and Okayama Prefectures.
Podocerus setouchiensis sp. nov. is similar to P. andamanensis (Giles, 1890), P. casuarinensis Kilgallen, 2009, P. crenulatus Myers, 1985, P. fulanus J.L. Barnard, 1962, P. lazowasemi Baldinger & Gable, 1994, P. orontes Hughes, 2013, and P. walkeri Rabindranath, 1972 in having dorsal carinae on pereonites 6 and 7, and pleonites 1 and 2. However, this new species differs from these species by the features shown in the following key. Podocerus setouchiensis sp. nov. is also similar to P. ulreungensis Kim & Kim, 1991 from Ulleung Island in the Sea of Japan in having antenna 2 with elongate flagellar article 1, gnathopod 1 with weakly lobate carpus, male gnathopod 2 merus pointed distally, male gnathopod 2 propodus with convex palmar margin bearing long marginal setae and robust seta at palm defining corner, uropod 1 peduncle with distoventral projection, and telson with 2 apical setae. However, this new species is distinguished from the latter by the following features (features of P. ulreungensis in parentheses): pereonite 6 with dorsal carina (absent); antenna 1 accessory flagellum 1-articulate (2-articulate); antenna 1 flagellar article 1 length 3.2 times as long as article 2 (2.3 times); uropod 2 peduncle with a short distoventral projection (lacking projection); and telson shorter than wide (longer).
1 | Uropods 1 and 2 with peduncular distoventral projection | 2 |
– | Uropods 1 and 2 without peduncular distoventral projection | 5 |
2 | Telson with 2 apical setae | P. setouchiensis sp. nov. |
– | Telson with 4 or 5 apical setae | 3 |
3 | Male gnathopod 2 palmar margin of propodus concave, with long plumose setae, lacking robust setae; uropod 3 without setae on rami | P. orontes Hughes, 2013 |
– | Male gnathopod 2 palmar margin of propodus convex, with short slender and robust setae; uropod 3 with setae on rami | 4 |
4 | Coxa of gnathopod 1 triangular; gnathopod 2 palmar margin of propodus with robust setae on proximal corner | P. fulanus J.L. Barnard, 1962 |
– | Coxa of gnathopod 1 subquadrate; gnathopod 2 palmar margin of propodus lined with robust setae | P. lazowasemi Baldinger & Gable, 1994 |
5 | Antenna 1 accessory flagellum 2-articulate | P. crenulatus Myers, 1985 |
– | Antenna 1 accessory flagellum 1-articulate | 6 |
6 | Uropod 1 inner ramus marginally bare | P. casuarinensis Kilgallen, 2009 |
– | Uropod 1 inner ramus with marginal robust setae | 7 |
7 | Male gnathopod 1 palmar margin of propodus almost straight | P. andamanensis (Giles, 1890) |
– | Male gnathopod 1 palmar margin of propodus convex | P. walkeri Rabindranath, 1972 |
We thank Dr Naohisa Nishihara and staffs of Satoumi Science Museum for their support with the field survey. Thanks are also due to Hiroshi Ogawa for providing materials and Dr Alan Myers for the critical reading and valuable comments on our manuscript. This study was partly supported by the Japan Society for the Promotion of Science KAKENHI grants JP 21H00919, JP22H01011, and JP22K06373 to KT.