Mithrax dichotomus Desmarest 1823

Mithrax dichotomus: authorship, date of publication and possible identity

The taxon known as Mithrax dichotomus has had a confused authorship and date of publication. Ng et al. (2008: 118) attributed the authorship and date of publication of Mithrax dichotomus to “ Latreille, 1831 ”. However, this name was actually not used in any publications by Latreille in 1831. Griffin & Tranter (1986: 244, 251) gave the author of this species as H. Milne Edwards, but cited “1934” as the year of publication. Prior to these two works, Heller (1863: 38) attributed authorship of this name to “Desmarest”, but with no date of publication indicated. Bouvier (1940: 325) attributed the species to Heller, and transferred it to Schizophrys White, 1848. Bouvier (1940: 325) also mentioned that various authors attributed the species to H. Milne Edwards who figured the species and that Heller (1863: 38, pl. 1 fig. 25) was the only author to give a detailed description and to figure the cheliped of the specimen.

Mithrax dichotomus was indeed treated by H. Milne Edwards (1831: [9], pl. 1; reproduced as Fig. 2A) but with authorship attributed to “Latreille” and the sentence “ M. Dichotomus. Desmarest op. cit. p. 150”. The species was again discussed and figured in H. Milne Edwards (1834a: 319; 1834b: pl. 15 figs. 1–4; reproduced as Fig. 2B). De Haan (1837: 94, pl. 22 fig. 4) figured a specimen, which was identified as Mithrax dichotomus, but which he subsequently recognised as a new species, Maja (Dione) affinis (De Haan, 1839: 94, pl. G) (see Holthuis, 1953: 37, 39). This species was considered to be a junior synonym of Schizophrys aspera (H. Milne Edwards, 1831) by Yamaguchi & Baba (1993: 359, fig. 117). Figures of the type material of Maja (Dione) affinis provided by Yamaguchi & Baba (1993) show that the species is morphologically similar to Schizophrys aspera (H. Milne Edwards, 1831). Bouvier (1940: 325, fig. 198, pl. 13 fig. 2) was doubtful of the locality information that was given by H. Milne Edwards for Mithrax dichotomus, and mentioned that it is likely the species were imported from the Indian Ocean, or from the Balearic Islands in the western Mediterranean. Although the figure of Mithrax dichotomus by Bouvier (1940: pl. 13 fig. 2) states that it is the “photo du type provenant des Baléares”, we are not (and can never be) sure if this is one of the actual types as no specific locality was originally given for Mithrax dichotomus by Desmarest (1823: 264). It is possible that the specimen figured by Bouvier (1940: 325, fig. 198, pl. 13 fig. 2) was the specimen examined and figured by H. Milne Edwards (1834a: 319; 1834b: pl. 15 figs. 1–4) leading Bouvier (1940: pl. 13, fig. 2, caption) to incorrectly conclude that this was the “ type ”.The earliest (and first available) use of the name Mithrax dichotomus is in fact by Desmarest (1823: 264), who diagnosed Mithrax dichotomus as follows:

“ Mithrax dichotome; Mithrax dichotomus, Latr.; Maia condyliata, Risso? Tête ovale oblongue, granuleux, sans épines en dessus à cinq ou six dents latérales, et terminé en avant par deux épines qui sont elles-mêmes divisées chacune en deux pointes. De la Méditerranée.”

It is clear that Desmarest (1823: 264) considered Latreille to be the author of the species. Ng et al. (2008: 20) discussed the confusion in authorship that resulted from the use of many manuscript or label names in the Paris Muséum (now MNHN) where Latreille worked, and the case of Mithrax dichotomus is no different. As the use of Mithrax dichotomus by Desmarest (1823: 264) is the earliest, and his diagnosis that accompanied the name makes it available, the correct author and date citation of the name must be Mithrax dichotomus Desmarest, 1823.

The type locality for Mithrax dichotomus has been reported to be the Mediterranean Sea (Desmarest, 1823: 264). As discussed earlier, it is possible that this record was based on the specimen reportedly from the Balearic Islands (see Bouvier, 1940: 325, pl. 13 fig. 2). Very little is known about this species with few published records of this species. The species was never found again from the same area or anywhere else after it was described (d’Udekem d’Acoz, 1999: 190).

An additional nomenclatural issue connected to Mithrax dichotomus needs to be discussed. Desmarest (1858: 14) designated Mithrax dichotomus as the type species of Mithrax Latreille, 1816. Ng et al. (2008: 123) mentioned that “E. Desmarest (1858: 14) lists ‘ Mithrax dicotomus Latr. ’ as the type, but to our knowledge this name has never been published, and so must be regarded as a nomen nudum ”. Although Mithrax dichotomus is an available name (as discussed above), the designation of Mithrax dichotomus as the type of Mithrax Latreille, 1816, is also invalid because this species was not an originally included species in Mithrax Latreille, 1816 (see Ng & Low, 2010: 38; Windsor & Felder, 2014: 162; 2017: 232).

Mithrax dichotomus has been recognised as a species of Schizophrys since Bouvier (1940: 325, fig. 198, pl. 13 fig. 2). Within the genus, there is no known record of any species of Schizophrys from the Mediterranean Sea, with the exception of S. dichotomus. Even Bouvier (1940: 325) had his doubts about the origins of the specimen, commenting “[l]es exemplaires qui le représentent et qui sont conservés au Muséum proviennent-ils bien des Baléares où jamais l’espèce n’a été retrouvée depuis? cela parait pour le moins douteux.” (see also d’Udekem d’Acoz, 1999: 190). Schizophrys dichotomus has never been recorded again since the original description.

Based on the description by Desmarest (1823: 264), it is likely that there may have been more than one type specimen. The repository for the type material of this species is likely the Muséum national d’Histoire naturelle, Paris, France (MNHN), but we have not been able to find the specimen within the museum despite several attempts; it is very likely no longer extant. We have also not been able to find the specimen from the Balearic Islands figured by Bouvier (1940), which may be a type. As all the type material cannot be located, the exact taxonomic identity of this species cannot be determined. It will almost certainly require an appropriate neotype selection to fix this name, but this should only be done as part of a full revision of the genus. For the moment, we follow Ng et al. (2008: 118) in regarding Mithrax dichotomus Desmarest, 1823, as a valid species of Schizophrys.