Pseudogeoplana nigrofusca ( Darwin, 1844 )

Luna, Manuel De & Boll, Piter Kehoma, 2023, An annotated checklist of terrestrial flatworms (Platyhelminthes: Tricladida: Geoplanidae) from Mexico, with new records of invasive species from a citizen science platform and a new nomen dubium, Zootaxa 5297 (4), pp. 518-532 : 522-523

Pseudogeoplana nigrofusca ( Darwin, 1844)

Figs. 8, 9 .

von Graff (1899a, as Geoplana nigrofusca : 297–298; fig. 35; MEXICO: Tabasco).

von Graff (1899b, as Geoplana nigrofusca : figs. 1–2 [in Table II]).

Ogren & Kawakatsu (1990: 157; catalog).

Ogren et al. (1997: 78, 82, 93; catalog).

External diagnosis. Not available, see below.

Remarks. This species was described from Maldonado, Uruguay, by Darwin (1844) and there is no type material known. The specimens illustrated by von Graff (1899a, 1899b) were collected by Hermann von Ihering from Rio Grande do Sul, Brazil; Graff also mentioned specimens from Mexico (from Frontera in the state of Tabasco) which were collected by C. H. Tyler Townsend in 1897. von Graff’s description and illustrations differ from Darwin’s description in that they depict a specimen with a much lighter colored dorsal margin and a marbled pattern, characters that are not mentioned by Darwin, who described the dorsum of the Uruguayan specimens as “uniform blackish brown”. von Graff’s description of the coloration on the ventral side of the animal states that it is orange on the sides and grayish yellow in the center, whereas Darwin described the venter of this species as just “pale”. The lighter-colored margins are cited in subsequent references, even as characteristic of the species ( Froehlich 1955), despite not originally being described as such. Given the difference in coloration and that the genital structure of Darwin’s specimen is unknown, we can theorize that the original Uruguayan and the subsequent Brazilian, Paraguayan, and Mexican specimens are not conspecific.

The description given by von Graff for the Brazilian specimens falls within the color variation found in Obama nungara Carbayo, Álvarez-Presas, Jones & Riutort, 2016 , a species native from southern Brazil, Uruguay and Argentina that recently has become invasive in Europe ( Lago-Barcia et al. 2015; Carbayo et al. 2016). von Graff’s drawing of the copulatory apparatus also has the typical appearance of that of Obama nungara ( von Graff 1899a; Carbayo et al. 2016). He also mentions that Geoplana nigrofusca is difficult to differentiate from Geoplana rufiventris Schultze & M̧ller, 1852, although he was probably referring to specimens of Obama marmorata (Schultze & M̧ller, 1857), a species that he had erroneously considered a synonym of Geoplana rufiventris ( von Graff 1899a) . Since Obama nungara was originally mistaken for Obama marmorata ( Lago-Barcia et al. 2015) , the probability of Pseudogeoplana nigrofusca sensu Graff and Obama nungara being the same species becomes even greater. Because there is no Type material or illustrations that could be designated as Pseudogeoplana nigrofusca , and because Darwin’s original description is too vague to accurately identify this species, we propose that Pseudogeoplana nigrofusca (synonymy: Planaria nigro-fusca , Geoplana nigro-fusca , and Geoplana nigrofusca ) should be treated here onwards as a nomen dubium. Specimens externally akin to what von Graff (1899a) and Froehlich (1955) describe are found in Mexico, as evidenced by records from the iNaturalist platform (#115484817, #138508028, #20769384, #64066094).

Figures

FIGURES 8–9. Pseudogeoplana nigrofusca sensu von Graff (1899a, 1899b): (8) illustration of the dorsal aspect of a living specimen (fig. 1 of plate II of von Graff [1899b]); (9) illustration of the dorsal aspect of a fixed specimen missing a piece of integument (fig. 2 of plate II of von Graff [1899b]). Scales not available.