Research Article |
Corresponding author: Hiroyuki Yoshitomi ( hymushi@agr.ehime-u.ac.jp ) Academic editor: Aaron Smith
© 2020 Hiroyuki Yoshitomi, Masakazu Hayashi.
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:
Yoshitomi H, Hayashi M (2020) Unexpected discovery of a new Podonychus species in Kyushu, Japan (Coleoptera, Elmidae, Elminae, Macronychini). ZooKeys 933: 107-123. https://doi.org/10.3897/zookeys.933.48771
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Podonychus gyobu sp. nov., a second species of the genus Podonychus Jäch & Kodada, 1997, hitherto known only from Indonesia, is described from Kyushu, Japan. This new species is similar to P. sagittarius Jäch & Kodada, 1997, but differs from it in the straight penis, arcuate 2nd labial palpomere, and in the 3rd antennomere being longer than wide. The endophallic structures and the larva of P. gyobu sp. nov. are described. A character matrix of the Macronychini genera and a key to the Japanese genera are provided.
disjunct distribution, endophallus, larvae, new species, riffle beetle, SEM, taxonomy
The riffle beetle fauna of Japan is well studied and 17 genera with 57 species are reported so far (
The genus Podonychus Jäch & Kodada, 1997 (Elminae, Macronychini) was hitherto known only from Siberut Island, Indonesia (
In the present paper, we describe this new species including endophallic structures and the larva.
Adults and larvae were collected from rivers by using small hand nets. The larval determination was done by association and by rearing. In Iroha-gawa (river) eight elmid species were collected (Podonychus gyobu sp. nov.; Leptelmis gracilis Sharp, 1888; Stenelmis nipponica Nomura, 1958; S. vulgaris Nomura, 1958; Grouvellinus nitidus Nomura, 1963; Zaitzevia awana (Kôno, 1934); Zaitzeviaria ovata (Nomura, 1959); Z. brevis (Nomura, 1958)); the larvae of all these species, except Podonychus gyobu, are included in the key by
The holotype and some paratypes will be deposited in the Ehime University Museum, Matsuyama, Japan (
Morphological terms used to describe the genitalia and the larva follow
General observations and dissections were made under a stereoscopic microscope (Leica MZ95). Microstructures of the dissected parts were mounted on hollow slides with pure glycerine and observed under a microscope (Olympus BH-2). After observation, the dissected parts were mounted on slides with Canada Balsam. SEM photographs were taken using a scanning electron microscope (JCM-6000 Neoscope; JEOL Ltd., Tokyo, Japan).
Morphological abbreviations used in this study are as follows:
EL length of elytra
PW width of pronotum
EW width of elytra
PL length of pronotum
TL total length (EL + PL)
The average measurement is given in parentheses after the range. For male genitalia, we made the following measurements after
BL basal length of penis, from base to the point where MH and ML lines meet
C degree of angle at MH point, formed by LBP and LCP lines crossing
CL caudal length of penis (= ML−BL)
LB length of phallobase
LBP length of basal portion, line connecting base with MH point
LCP length of caudal portion, line connecting MH point with apex
MH maximum height of penis, vertical line from ML line to C point
ML maximum length of penis (= BL+CL)
Podonychus sagittarius Jäch & Kodada, 1997
The genus is very distinctive in having the following characteristics of the adults (see also Table
Character matrix of Macronychini genera. Abbreviations: parameres (a = absent; p = present); basal piece (s: short; l: long); hind wing (B: brachypterous; M: macropterous; MI: micropterous).
Genus | Antennal segment no. | Parameres | Labial palpo-meres no. | Basal piece | Hind wing | Elytral carinae | Distribution | References |
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Eonychius | 10 | a | 3 | s | B | V-VII-VIII | China (Hong Kong) |
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Vietelmis | 10 | p | 3 | s | M | V-VII, V-VII-VIII | Vietnam, China, Borneo, Laos, Thailand, Malaysia |
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Haraldaria | 9 | a | 3 | s | B | V-VI-VII | Malaysia |
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Homalosolus | 9 | a | 3 | l | M/B | V-VII-VIII, III-V-VII-VIII | Borneo |
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Aulacosolus | 8 | a | 2 | s | M | V-VII, III-V-VII, III-V-VII-VIII | India, Thailand, Laos, Malaysia, Indonesia (Sumatra) |
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Cuspidevia | 8 | p | 3 | s | M | VII | China |
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Graphosolus | 8 | a | 2 | s | B | III-V-VII-VIII | Borneo, Indonesia (Sumatra, Java), Malaysia, Philippines |
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Indosolus | 8 | a | 2 | s | M | V-VI-VII | Myanmar, India, China, Malaysia |
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Jilanzhunychus | 8 | a | 3 | s | B | III-V-VII-VIII | China |
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Loxostirus | 8 | a | 2 | s | B | III-V-VII-VIII | Borneo |
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Macronevia | 8 | p | 3 | s | M/B | V | Malaysia |
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Nesonychus | 8 | a | 2 | s | B | V-VII | Borneo, Indonesia (Sumatra, Java, Lombok) |
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Okalia | 8 | a | 3 | s | M/B | V-VI-VII | Malaysia | Kodada and Čiampor (2003) |
Paramacronychus | 8 | p | 3 | s | B | III-V-VII-IX, V-VII-IX | Japan |
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Rhopalonychus | 8 | a | 3 | s | M | VII-VIII | Borneo |
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Urumaelmis | 8 | p | 3 | s | M | V-VI | Japan |
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Zaitzevia | 8 | p/a | 3 | s | M/B | V-VI-VII, V-VII-VIII | India to China, Japan, Korea, Russian Far East, North America |
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Zaitzeviaria | 8 | p/a | 3 | s | M/B | VII-VIII | East Palearctic and Oriental Regions |
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Macronychus | 7 | a | 3 | s | M/B | III-V-IX | Europe, North Africa, Russian Far East, China, Korea, Oriental Region, North America |
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Prionosolus | 7 | a | 2 | s | M/B | V-VII | Philippines, Borneo, Indonesia (Siberut) |
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Sinonychus | 7 | a | 2 | s | B | III-V-VI-VII, V-VI-VII | China, Japan |
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Podonychus | 6 | a | 2 | s | MI | VIII | Indonesia (Siberut), Japan |
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Holotype
(
3 mature larvae (
Podonychus sagittarius Jäch & Kodada, 1997: 1 male paratype (
The new species is morphologically similar to P. sagittarius, and differs from it in the following characteristics: 1) penis almost straight from base to near apex in lateral view (slightly curved ventrally in P. sagittarius); 2) lateral margins of the 2nd labial palpomeres strongly arcuate (weakly arcuate in P. sagittarius); 3) 3rd antennomeres longer than wide (as long as wide in P. sagittarius). The endophallicstructures of P. sagittarius were not described in detail, but judging from the aedeagus illustrations (
Body (Fig.
Adult of Podonychus gyobu sp. nov. A dorsal habitus without elytra B head in lateral view C labium D aedeagus with everted endophallus E basal tube of endophallus F spines on basal tube of endophallus G apical tube of endophallus H ditto, close up. AT: apical tube; BT: basal tube; gp: gonopore.
Head with sparse suberect setae. Eyes small with about 40 facets. Antennae 6-segmented; approximate ratio of length of antennomeres 1–6: 6 : 7 : 6 : 2 : 3 : 14 (N = 1, paratype). Maxillae (Fig.
Male. Tergite VIII (Fig.
Female. Tergite VIII (Fig.
Measurement (N = 10). TL 1.21–1.36 (1.28) mm; PW 0.37–0.45 (0.41) mm; PL 0.37–0.43 (0.40) mm; EL 0.82–0.95 (0.87) mm; EW 0.51–0.60 (0.56) mm.
Body (Fig.
Head visible dorsally, well exposed from prothorax, trapezoidal, widest at apical 1/3, densely covered with short spines, bearing short setae. Eyes (Fig.
Larva of Podonychus gyobu sp. nov. A abdominal segments IV–VIII in dorsal view B abdominal segments IV–VIII in lateral view C abdominal segments V–IX in ventral view D abdominal segments VIII–IX in dorsal view E apex of abdominal segment IX in dorsal view F surface of abdominal segment IX in lateral view G abdominal segments VIII–IX in ventral view H operculum.
This species lives in small rivers at low elevation. Larvae and adults were collected from submerged roots of reeds using a net. They were collected with Elmomorphus brevicornis Sharp, 1888 and Stenelmis nipponica Nomura, 1958.
So far, this species is known only in the Iroha and Yakkan river systems, in the eastern part of Kyushu, Japan.
“Gyobu” is an NPO (nonprofit organization) in Kitakyushu, Fukuoka. This new species was discovered during a survey of water beetle fauna by Mr D. Inoue, president of “NPO Kitakyushu Gyobu”. The epithet is a noun in apposition.
1 | Body oval, somewhat convex dorsally, shorter than 1.5 mm in TL | 2 |
– | Body oblong, relatively flat dorsally, longer than 1.5 mm in TL | 4 |
2 | Antennae 8- or 7-segmented; humeri developed | 3 |
– | Antennae 6-segmented; humeri reduced | Podonychus |
3 | Antennae 7-segmented; lateral margin of elytra serrate | Sinonychus |
– | Antennae 8-segmented; lateral margin of elytra not serrate | Zaitzeviaria |
4 | Lateral declivity of pronotum with impressions | 5 |
– | Lateral declivity of pronotum without impressions | Paramacronychus |
5 | Elytra with carinae on intervals V, VI, VII or V, VII, VIII | Zaitzevia |
– | Elytra with carinae on only anterior part of intervals V and VI | Urumaelmis |
1 | Dorsum with longitudinal stripes of granules; sides of thorax serrate; thorax and abdomen with Y-shaped projections attaching on caudal margins; apex of abdominal segment IX serrate | Podonychus |
– | Dorsum without stripes of granules; sides of thorax not serrate; thorax and abdomen lacking Y-shaped projections; apex of abdominal segment IX with a small notch | 2 |
2 | Coloration of body entirely orange; abdominal segment IX distinctly convex ventrally | Paramacronychus |
– | Coloration of body entirely pale brown, dark brown or black; abdominal segment IX flat ventrally | 3 |
3 | Cross-section of body triangular; coloration of body entirely pale brown | Zaitzeviaria |
– | Cross-section of body semicircular; coloration of body entirely black or dark brown | Zaitzevia |
Podonychus is currently known only from Indonesia and Kyushu, Japan, representing a disjunct distribution across the equator. We think this genus is probably distributed more widely in the Oriental Region but has not been found in other areas because of the small body size and unusual microhabitat. All specimens of the new species were collected from the submerged roots of reeds, and we think this microhabitat is important for the genus. In the future, additional species of this genus are expected to be discovered from east and southeast Asia, e.g., China, Taiwan, Vietnam, and the Philippines.
Podonychus sagittarius was collected from a small stream densely shaded by forest (
The endophallic structures of Podonychus, with a well sclerotized long apical tube, are unique not only in the tribe Macronychini, but also in the family Elmidae. The endophallic structures within the family are usually membranous as is probably the case in many Coleoptera (
The larval morphology of this genus is unique, particularly in having Y-shaped projections (Fig.
We thank Daisuke Inoue, who first discovered this new species, Dr Jun Nakajima, Yuta Kudo and Takuro Kumagae for their kind support in field research, and Dr Manfred A. Jäch (