Procrangonyx Schellenberg, 1934

Nakano, Takafumi, Tomikawa, Ko & Grygier, Mark J., 2018, Rediscovered syntypes of Procrangonyx japonicus, with nomenclatural consideration of some crangonyctoidean subterranean amphipods (Crustacea: Amphipoda: Allocrangonyctidae, Niphargidae, Pseudocrangonyctidae), Zootaxa 4532 (1) : -

Genus Procrangonyx Schellenberg, 1934

Procrangonyx Schellenberg, 1934: 217 –218.— Bousfield, 1977: 306.— Holsinger, 1977: 248 (in discussion).— Barnard & Barnard, 1983: 444 –445.— Holsinger, 1986: 542.— Holsinger, 1989: 956.— Stock & Jo, 1990: 119 (as an unavailable name without type species designation).— Tomikawa & Shinoda, 2016: 584 –585 (as an unavailable name).

Eocrangonyx Schellenberg, 1937a: 37 (type species: Eucrangonyx japonicus Uéno, 1930 , fixed by monotypy).— Barnard & Barnard, 1983: 444 (as a junior synonym of Procrangonyx ).— Bousfield, 1983: 272.— Stock & Jo, 1990: 121.

Eocrangonyx Schellenberg, 1934 (sic).— Ishimaru, 1994: 41 (attribution only, without corresponding reference).— Tomikawa & Morino, 2012: 41 (attribution only, without corresponding reference).

Eocrangonyx Schellenberg, 1936 (sic).— Holsinger, 1977: 248 (in discussion, as a junior synonym of Procrangonyx ).— Holsinger, 1989: 956 (as a junior synonym of Procrangonyx ).— Sidorov & Barabanschikov, 2010: 70 (in discussion, as a junior synonym of Procrangonyx ).— Tomikawa & Shinoda, 2016: 584.—Tomikawa et al., 2016: 200 (in discussion).

Type species: Eucrangonyx japonicus Uéno, 1930 , fixed by monotypy.

Nomenclatural history. C.S. Bate (1859) —the citation of Charles Spence Bateherein follows Clark (2018) — established a new genus, Crangonyx C.S. Bate, 1859 , for a single new subterranean species, C. subterraneus C.S. Bate, 1859 , which was collected from Ringwood, U.K. The type species of Crangonyx was thereby fixed as C. subterraneus by monotypy, but C.S. Bate provided no morphological details of the uropods. Later, Stebbing (1899) erected a new Crangonyx -like genus, Eucrangonyx Stebbing, 1899 , for subterranean amphipods with a biramous uropod 3, i.e., with both inner and outer rami. He included five species in this new genus but did not designate its type species; one of the originally included five species, Crangonyx gracilis Smith in Smith & Verrill, 1871 , was subsequently designated as the type species of Eucrangonyx by Chevreux & Fage (1925).

Much later, Uéno (1930) described a Japanese subterranean amphipod collected from Tokyo as Eucrangonyx japonicus Uéno, 1930 . He highlighted the fact that its uniramous (with outer ramus only) uropod 3 was uniarticulate, contrary to the condition in the Asian subterranean amphipod genus Pseudocrangonyx Akatsuka & Komai, 1922 , whose authors had diagnosed it by the uniramous but biarticulate uropod 3.

Schellenberg (1932) examined non-type material of the British C. subterraneus and reported that this species has a rudimentary inner ramus on uropod 3, which is therefore biramous. Referring to this work again two years later, Schellenberg (1934) concluded that the generic name Eucrangonyx is a junior subjective synonym of Crangonyx , the latter being diagnosed by a biramous uropod 3. At the same time he proposed a new generic name, Procrangonyx Schellenberg, 1934 (p. 217), for the species with a uniramous uropod 3 that had been previously classified under Eucrangonyx . Throughout the (German) text, he referred to these uniramous “species” in the plural (i.e., as “Arten”), which indicates that his concept of the genus comprised more than one species. Schellenberg (1934) did not designate a type species for Procrangonyx , but he did explicitly mention a single species, E. japonicus (cited as Procrangonyx japonicus ), as “an example” of such a uniramous species (p. 218): ‘ … ist er bei anderen Arten, z. B. Procrangonyx japonicus (Uéno, p. 22), Pseudocrangonyx (l. c.) einästig, ….’ Although Schellenberg did not cite Eucrangonyx japonicus in its original combination, there can be no doubt about the identity of the species involved. He explicitly attributed Procrangonyx japonicus to Uéno (1930), whose work includes on page 22 a figure showing the uniramous uropod 3 of E. japonicus and the description of this uropod. Schellenberg (1934) also listed Uéno’s (1930) work in his references section.

Three years after the initial proposal of Procrangonyx, Schellenberg himself (1937a) established a new genus, Eocrangonyx Schellenberg, 1937a , with a detailed diagnosis. He included one species in it, Eocrangonyx japonicus ( Uéno, 1930) cited as follows (p. 37): ‘ E. japonicus (Uéno) 9 mm, Wasserwerk Tokyo.’ Eucrangonyx japonicus was thereby fixed as the type species of Eocrangonyx , by monotypy. Schellenberg (1937a) never mentioned Procrangonyx .

When erecting the new family Pseudocrangonyctidae consisting of Pseudocrangonyx and Procrangonyx, Holsinger (1989) treated Eocrangonyx as an objective junior synonym of Procrangonyx and stated that the type species of Procrangonyx is Eucrangonyx japonicus Uéno, 1930 fixed by monotypy. Holsinger’s contentions were, however, not supported by explicit citations of relevant provisions of the Code. In contrast, Stock & Jo (1990: 120– 121) pointed out that the expression “z. B.” (i.e., “zum Beispiel”, meaning “for example”) in the original description of Procrangonyx cannot be regarded as a type species designation according to Article 67(c) of the International Code of Zoological Nomenclature, Third Edition (International Commission on Zoological Nomenclature 1985). They judged the generic name Procrangonyx to be unavailable because, as they saw it, the genus was erected without a type species after 1930, contrary to the Third Code’s Article 67(c)(1). In place of Procrangonyx Stock & Jo (1990) used the available name Eocrangonyx for the Japanese species, and they also described a new Far-East Russian species as Eocrangonyx primoryensis Stock & Jo, 1990 .

After 2000, Hou & Li (2003) and Sidorov & Holsinger (2007) each described a new subterranean amphipod species with a uniramous and uniarticulate uropod 3, the two species being placed in Procrangonyx as P. limpidus Hou & Li, 2003 and P. stygoedincus Sidorov & Holsinger, 2007 . Neither work referred to Stock & Jo (1990). Later, Sidorov & Barabanschikov (2010: 70–71) cited Stock & Jo (1990) and argued that the earlier name Procrangonyx was valid. Additionally, they treated P. stygoedincus as a subjective junior synonym of P. primoryensis ( Stock & Jo, 1990) , the latter being shifted to this genus from Eocrangonyx .

Tomikawa & Shinoda (2016) redescribed Eucrangonyx japonicus Uéno, 1930 . Citing relevant provisions of the current Fourth Edition of the Code (International Commission on Zoological Nomenclature 1999), they reaffirmed Stock & Jo’s (1990) nomenclatural conclusion on the invalidity [sic; unavailability was meant] of Procrangonyx and used the binomen Eocrangonyx japonicus (pp. 584–585). Following Tomikawa & Shinoda (2016), all species assigned to Procrangonyx were placed under Eocrangonyx in the influential web resource WoRMS—in which amphipod records are sourced from World Amphipoda Database (= WAD) ( Horton et al. 2018a)—, the former genus being treated there as an invalid name without type species designation. In accordance with the manual for editors of WoRMS (Available from: http://www.marinespecies.org/aphia.php?p=manual#top; see also Horton et al. 2017), Procrangonyx was treated in the same way as the “present literature” does, i.e., as an “unaccepted” (= “invalid”) name that lacks a type species designation; however, a note acknowledged the ongoing disagreement on this latter point.

Nomenclatural conclusion. In considering the potential availability and validity of Procrangonyx , it is necessary to clearly distinguish the two concepts of type species “fixation” (Article 67.4 of the Code) and type species “designation” (Article 67.5). The nomenclatural arguments of both Stock & Jo (1990) and Tomikawa & Shinoda (2016) were partially correct in that Schellenberg (1934) did not “designate” Eucrangonyx japonicus as the type species of Procrangonyx in a manner recognized by Article 67.5 of the Code. Under Article 67.2.1 and Article 68.3, however, because Procrangonyx japonicus ( Uéno, 1930) was the only available nominal speciesgroup taxon originally included in Procrangonyx , this species ( Eucrangonyx japonicus in its original combination) was fixed by Schellenberg (1934) as the type species of Procrangonyx . [N.B.: Under Recommendation 67B of the Code, the name of a type species should be cited by its original binomen.] Since a type species was “fixed” in the original publication, even if not explicitly “designated”, and a diagnostic character for the genus was proposed in the same work, Procrangonyx Schellenberg, 1934 is available and is the valid name of the genus. Eocrangonyx Schellenberg, 1937a , with the same type species, is then a junior objective synonym of Procrangonyx , and as such is invalid.

Holsinger (1989) was unquestionably correct about the availability and the type species fixation of Procrangonyx , despite his lack of rigorous reference to the Code. The erroneous status of Procrangonyx and Eocrangonyx in WAD should be emended promptly to avoid additional confusion about which generic name to use for the species now assigned to these genera. The nomenclatural disorder concerning the availability, and thus the validity, of Procrangonyx highlights the common error of confusing the two terms “ type fixation” and “ type designation”. Zoologists are generally aware that to be available, every new genus-group name proposed after 1930 must be accompanied by type species “fixation”, but, like Stock & Jo (1990) they tend to misunderstand this to mean “original designation” by the author of the genus. Indeed, explicit designation is probably best practice, but several other permissible means of type species fixation are also listed in Article 68 of the Code: monotypy, absolute tautotomy and “Linnean tautotomy”. In the present instance, type species fixation occurred by monotypy in the original publication.