First record of the terrestrial amphipod, Talitroides alluaudi (Chevreux, 1896) (Crustacea, Amphipoda, Brevitalitridae), from Japan

We report Talitroides alluaudi (Chevreux, 1896) from Miyako Island, Ryukyu Islands, Japan. Although this terrestrial amphipod is distributed worldwide, including Indo-Pacific islands, Europe, and North and South America, the present specimens represent the first record of this species from Japanese islands. The cytochrome c oxidase subunit I (COI) sequence of a Miyako Island specimen was unique compared with the known COI sequences from Taiwanese and Bermudan populations.


Introduction
Terrestrial amphipods known as talitrids-members of Talitroidea herein-have invaded various inland habitats (Bousfield 1984). They were previously classified into a single family, Talitridae; however, this family was recently split into seven families by Myers and Lowry (2020). Talitroides Bonnier, 1898 is a genus in the family Brevitalitridae, which is one of the seven newly erected families. This genus consists only of two species, Talitroides alluaudi (Chevreux, 1896) and Talitroides topitotum (Burt, 1934). Talitroides topitotum is globally distributed (Nascimento and Serejo 2016) and was even reported from Okinawa Island in the Ryukyu Islands, Japan (Morino 2013). Although T. alluaudi was also recorded from various locations worldwide, to our knowledge, this species has not been found anywhere in the Japanese Archipelago, including the Ryukyu Islands. A review by Nascimento and Serejo (2016) and a study by Wildish et al. (2016) revealed that T. alluaudi inhabits islands in the Indian Ocean, southern Pacific and northern Atlantic, Hawaii, Israel, Europe, North America, and Brazil (Fig. 1A). In addition to those locations, a master's thesis (Chiang 2012), which was overlooked in the previous studies, recorded this species from Taiwan (Fig. 1B).
In this study, we collected a lot of talitrids living inside rotten wood on Miyako Island in the Ryukyu Islands, Japan. We successfully identified all of them as T. alluaudi on the basis of both morphological characters and the mitochondrial DNA sequence of a specimen. Therefore, we report this species for the first time from Japan.

Methods
We collected the amphipods with rotten wood found in an inland forest, which is located ~2 km from the nearest beach, on Miyako Island, Ryukyu Islands, Japan (Fig. 1B,C) and brought them to the laboratory. In the laboratory, we separated the amphipods from rotten wood using a pooter, and then preserved them in 99% ethanol. We observed and dissected the specimens with a Leica M125C stereoscopic microscope. Detailed characteristics of the dissected specimens were inspected using an Olympus BX53 light microscope and the Leica M125C.
An image of the whole body was captured with a Leica MC170 HD digital camera mounted on the Leica M125C, and prepared using Leica Application Suite v. 4.12 software. Images of body parts were prepared with a Canon EOS Kiss X7 digital camera mounted on the BX53. We deposited the examined specimens in the Zoological Collection of Kyoto University (KUZ).
The COI sequence obtained, which yielded 658 bp aligned positions, showed three different loci when compared with the known sequences from Taiwan and Bermuda (Table 1). The Taiwanese and Bermudan sequences, which showed 617, 635, or 658 bp aligned positions, were identical to each other. All substitutions detected between the Miyako individual and Taiwanese and Bermudan samples were synonymous.

Discussion
The present specimens clearly showed diagnostic characters of Talitroides-cuspidactylate pereopods, reduction in rami of pleopods, L-shaped coxal gill of pereopod 6-and can be unquestionably identified as T. alluaudi because they possessed the following features: small body size whose body length ~7 mm, antenna 1 flagellum with ~5 articles, antenna 2 flagellum with fewer than 12 articles, pereopod 4 dactylus with dentation, and uropod 1 with simple distolateral robust setae (see Nascimento and Serejo 2016). Although several characteristics of the examined Miyako specimens differed from the T. alluaudi lectotype, i.e., antenna 1 flagellum with 5 articles, pereopod 3 dactylus nail with a sharp dentation posteriorly, and pereopod 5 dactylus nail with a slight prominence at middle on the anterior margin, those characteristics seem to be intraspecific variations of this species (Morino and Ortal 1993;Nascimento and Serejo 2016). Our genetic analysis of the COI sequences also corroborated that the Talitroides specimens on Miyako Island belong to T. alluaudi.
Around the Pacific Ocean, T. alluaudi has been reported from Southeast Asia (Stephensen 1935), the Australian region (Friend and Richardson 1986), Melanesia (Hurley 1975), French Polynesia (Stephensen 1935), the Hawaiian Islands (Bousfield and Howarth 1976;Richardson 1991), and Taiwan (Chiang 2012). This species inhabits Miyako Island and Taiwan, and therefore may also be distributed in other islands in the Ryukyu Islands, such as the Yaeyama Islands, which are located between Miyako Island and Taiwan. Although the Miyako and Taiwanese populations are geographically close to each other, their COI sequences showed that they were clearly distinct. Moreover, the Taiwanese sequence was similar to those obtained from Bermudan T. alluaudi. Given the global distribution of T. alluaudi, which was originally described from Paris, France (Chevreux 1896), this species is thought to have widely dispersed by synanthropic means (Nascimento and Serejo 2016;Wildish et al. 2016); moreover, its natural habitats remain unknown (Friend and Richardson 1986). The COI sequence results revealed the occurrence of genetic variations among geographical populations, which suggests that future analyses of genetic variations among T. alluaudi populations covering the distribution of this species may clarify the dispersal history of this species and may also elucidate whether T. alluaudi expands its range via human activities.