Petrolisthes

Osawa, Masayuki & Uyeno, Daisuke, 2013, A new subtidal species of the genus Petrolisthes Stimpson, 1858 (Crustacea: Decapoda: Porcellanidae) from Okinawa, with an account of species of the genus known from the Ryukyu Islands, southwestern Japan, Zootaxa 3670 (3), pp. 329-338 : 335-336

Species of Petrolisthes known from the Ryukyu Islands

In the Ryukyu Islands, 27 nominal species of Petrolisthes are currently known, including the present new species: P. asiaticus ( Leach, 1820) ; P. bifidus Werding & Hiller, 2004 ; P. borradailei Kropp, 1984 ; P. carinipes ( Heller, 1861) ; P. celebesensis Haig, 1981 ; P. coccineus ( Owen, 1839) ; P. cyanochir Osawa & Maenosono, 2011 ; P. donanensis Osawa, 1997 ; P. extremus Kropp & Haig, 1994 ; P. fimbriatus Borradaile, 1898 ; P. hastatus Stimpson, 1858 ; P. haswelli Miers, 1884 ; P. heterochrous Kropp, 1986 ; P. holthuisi Hiller & Werding, 2010 ; P. j a p o n i c u s ( De Haan, 1849); P. lamarckii ( Leach, 1820) ; P. m a s a ki i Miyake, 1943; P. moluccensis ; P. obtusifrons Miyake, 1937 ; P. pubescens Stimpson, 1858 ; P. scabriculus (Dana, 1852) ; P. squamanus Osawa, 1996 ; P. tomentosus (Dana, 1852) ; P. trilobatus Osawa, 1996 ; P. unilobatus Henderson, 1888 ; P. uruma sp. nov.; P. virgatus Paul’son, 1875 ( Miyake 1943; Miyake & Nakasone 1966; Nakasone & Miyake 1968, 1972; Osawa 1996, 1997, 1998b, 2007; Osawa & Maenosono 2011; unpublished data). Among these species, despite the first author’s continuous survey of the porcellanid fauna in the Ryukyu Islands since 1992, P. fimbriatus has not been collected there since Miyake (1943) recorded the species from Ishigaki-jima Island, Yaeyama Islands. The specimen studied by Miyake (1943) was deposited in the Zoological Laboratory, Faculty of Agriculture, Kyushu University (ZLKU), and the crustacean collection of ZLKU was later transferred to the Kitakyushu Museum of Natural History and Human History (KMNH). However, our attempt to locate Miyake’s (1943) specimen was not successful. The specimen might actually represent P. obtusifrons , which is closely similar to P. fimbriatus and one of the relatively common intertidal species in the Ryukyu Islands (Osawa 1998, as P. varicolor ). In the collection of KMNH, there is another specimen labeled as P. fimbriatus that was collected from Yoron-jima Island (Off Sena, one ovigerous female, cl 5.9 mm, 9 July 1968, ZLKU 14895). Re-examination of this specimen revealed that it is P. squamanus instead. Additionally, P. squamanus was also collected from the Palau Islands based on re-examination of one specimen identified as P. fimbriatus by Dr. S. Miyake (Meleiok, one female, cl 6.4 mm, 19 July 1939, ZLKU 15015), although this specimen is not used in his studies (1942, 1943).

There are other records referred to species of Petrolisthes , of which identities have been clarified, as summarized below. Miyake (1937) described P. yaeyamensis Miyake, 1937 from Ishigaki-jima Island, but Miyake (1943) later synonymized this taxon under P. a s i a t i c u s. Miyake (1943) recorded P. penicillatus Heller, 1962 from Ishigaki Island, but this Heller’s taxon was synonymized with P. tomentosus by the neotype designation for the latter taxon by Kropp (1986). The material identified as P. tomentosus by Miyake (1943) was referred to P. pubescens (cf. Kropp 1986). Although Nakasone & Miyake (1968) reported P. indicus De Man, 1893 (now placed in the genus Novorostrum Osawa, 1998 ) from Iriomote-jima Island, Osawa (1998a) concluded that their specimens belong to his new species Novorostrum decorocrus Osawa, 1998 . The records of P. militaris ( Heller, 1862) from the Ryukyu Islands by Osawa (1996, 1998b) are referred to P. holthuisi (unpublished data). Osawa (1998b) described P. varicolor Osawa, 1998 from the Ryukyu Islands and Phuket in Thailand, but Osawa (2007) later regarded it a junior synonym of P. obtusifrons based on the re-examination of the holotype of the latter species. In addition, the taxonomic relationship of P. lamarckii with its presumed synonyms is still unresolved ( Kropp 1984; Osawa & Chan 2010; Osawa & McLaughlin 2010). In fact, specimens from the Ryukyu Islands referable to P. lamarckii are separated into more than two morphs based on the morphological characters and coloration, suggesting the existence of more than one species.

Petrolisthes cyanochir is so far known only from the Ryukyu Islands. However, close resemblance of the morphology between P. cyanochir and the P. lamarckii species complex suggests that the former species might have been misidentified as P. lamarckii or its related species in the previous studies based on specimens from outside the Ryukyu Islands, though P. cyanochir is distinguishable from the P. lamarckii species complex by the shape of the carapace and the poorly developed or no epibranchial spine ( Osawa & Maenosono 2011). There are no records of P. decacanthus Ortmann, 1897 and P. miyakei Kropp, 1984 from the Ryukyu Islands, although these two species are found in the eastern and southern coasts of Taiwan, next to the western end of the Ryukyu Archipelago ( Osawa & Chan 2010). The former species is mainly distributed in oceanic islands of the Indo-West Pacific, whereas the latter is known only from the Mariana Islands besides Taiwan ( Haig & Kropp 1987; Asakura et al. 1994). On the other hand, coral-reef inhabitants such as P. celebesensis , P. m a s a k i i, and P. trilobatus , are recorded from the Ryukyus, but these are not found in Taiwan probably because of restricted collecting efforts in coral reefs. More field investigations are still needed in the Ryukyu Islands and Taiwan to document the fauna and to evaluate biogeographical characteristics of the region of high biodiversity.