Gonyleptes planiceps Guerin-Meneville
Creators: name: Acosta, Luis E.
Publisher: name: Zenodo
Year: 2025
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Arachnida
Opiliones
Gonyleptidae
Gonyleptes
Gonyleptes planiceps

description: Gonyleptes planiceps and fig. 10
Confusion on Gervais’ (1854) plate ‘Arachnideos N°1’ affects Gonyleptes planiceps too, another species that had (taxonomically) ‘crossing destinies’ with G. bicornis. The original description and illustrations of G. planiceps are clear (Gervais 1842) and some early papers demonstrated a good notion of its identity (cf. Simon 1884: 141, 1887: 37, Pl. 2, fig. 9). Problems emerged with a further mismatch between redescription and figures of Gervais (1849, 1854) that (again) puzzled Sørensen and Roewer. Gonyleptes planiceps was treated by Gervais (1849: 24) and was explicitly referred to a line drawing of a male in dorsal view: fig. 10. The redescription is a verbatim translation to Spanish of the redescription of G. planiceps previously given by Gervais (1844).
Sørensen (1902) said (translation from Latin): ‘Whether this species [G. planiceps] belongs to the genus Lycomedes or to another genus, I really do not know. Description and figure [fig. 10] given by Gervais do not agree in any way. According to the description areas are divided by length, what the figure does not show – After the figure, five transverse grooves are present. (…) If the species can be determined, the paired eminences of the free dorsal segments and legs IV (male) would indicate species’. In the same publication, Sørensen (1902) happened to examine a MNHN male labelled “ Pachylus planiceps ” by E. Simon, concluding that it did not agree ‘with Gervais’ illustration’ [that of 1854 was meant!], but allegedly represented a new species instead, which he described as Balta meridionalis Sørensen, 1902 (pp. 21, 23). This puts in evidence that, despite of being aware of the text/drawings mismatch, Sørensen’s (1902) concept of Gonyleptes planiceps remained attached to Gervais’ (1854) fig. 10.
Types: Gervais (1842) did not explicit the original series of G. planiceps, but, as he described both sexes, at least one male and one female were available to him (thus, Roewer’s 1913: 136 statement “ ♀ unbekannt” [female unknown] is mistaken). During a meticulous survey of the “dry collection” in the NHMUK, I discovered one male and one female, pinned separately, undoubtedly belonging to the type series (as syntypes). The original label of the male specifies “ Gonyleptes planiceps Guer. ic. R.A. (type), Magellan”, that of the female just “Magellan”. These specimens had some appendages either lost or loose, so I transferred them to vials with 70 % ethanol, along with suitable labels (handwritten by me) to unequivocally indicate their type status. The labels of the male (NHMUK 013376526) are currently available at the NHM Data Portal: https://data.nhm.ac.uk/dataset/collection-specimens/ resource/05ff2255-c38a-40c9-b657-4ccb55ab2feb/record/8287232. Pessoa-Silva et al. (2020) took profit on this unpublished information to formally determine the validity of Gonyleptes planiceps as senior synonym of Balta meridionalis, what is in full agreement with my previous observations.
Roewer makes it worse: As purported in Roewer’s labels, this author believed that the specimen SMF RI/795 belonged to the type series of Gonyleptes planiceps (Acosta 1996a). The catalog-card in the SMF declares its presumed status too: “Simon ded., ex Museum Paris, 1 ♂ Paratypus!”. This is likely the MNHN specimen cited by Roewer (1913) as “ Lycomedes planiceps (Guérin) ”, which he seemingly incorporated later to his own collection (Roewer 1923). The morphology of this specimen (a male, initially dry preserved, examined) does not match the original description and illustrations of G. planiceps given by Gervais (1842), neither Gervais’ (1849) redescription; but it does match the male drawn by Gervais (1854) in his fig. 10! That is to say, specimen SMF RI/795 is actually conspecific with G. bicornis, as restored in this paper (see below). On the one hand, the alleged type status of SMF RI/795 is not supported (Acosta 1996a). On the other hand, Roewer followed Sørensen and gave preference to fig. 10 for identification, over the description.
Remarks: Roewer (1913) indicated that the MNHN material of Gonyleptes planiceps comes from around the Strait of Magellan, information seemingly inspired by the original description, not stated on any label. There is a second citation of “ Lycomedicus planiceps ”, also by Roewer (1923), where a male from “ Valparaiso ” (allegedly in his collection) is reported. Over several months I thoroughly revised all tubes of Pachylinae and the catalogues of Roewer’s Collection (Acosta 1996a), but just one specimen labeled as Lycomedicus planiceps was located, the already mentioned RI/795. Most probably the two citations refer to the same specimen, and the reference to “ Valparaíso ” is another of many inaccuracies in Roewer’s work. On the SMF catalog-card the species name was first written “ planiceps (Guer.), Lycomedes ”, then corrected to “ planiceps (Roewer), Lycomedicus ” (note the mistaken amendment of the authorship).
At this point it is needed to test the correspondence between Gervais’ (1854) fig. 10, and the description of Gonyleptes bicornis and redescription of G. planiceps in Gervais (1849); this is accomplished in Table 3, including (when applicable) features of the above mentioned fig. 4b (Gervais 1854) as well, which I also attribute to G. bicornis. Contrary to the uses of Gervais (1849), Sørensen (1902) and Roewer (1913), fig. 10 does not agree with the redescription of G. planiceps but with the description of G. bicornis instead. The conclusion of this thorough comparison is straightforward: Gonyleptes bicornis is to be referred to two mislabeled illustrations in the Atlas (Gervais 1854): fig. 4b and fig. 10. They show without doubt a hitherto undetected member of genus Parabalta: henceforth named Parabalta bicornis comb. nov.
description: Published as part of Acosta, Luis E., 2025, Deciphering a Chilean harvestmen enigma: what is Parabalta bicornis (Gervais, 1849) comb. nov. (Opiliones: Gonyleptidae: Pachylinae), pp. 193-208 in Zootaxa 5563 (1) on page 198, DOI: 10.11646/zootaxa.5563.1.13, http://zenodo.org/record/14595841