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Rhizosomichthys totae, the Pez Crasso, greasefish, or runcho of Lago de Tota, Colombia, is known from ten specimens and thought to be extinct. The species is unique among trichomycterids in possessing remarkable rings of extensive adipose tissues surrounding the body. Although its internal anatomy is poorly known, diagnosis of Rhizosomichthys totae and taxonomic status within Trichomycteridae have not been questioned. Non-destructive reconstruction of the osteology of one paratype based on computed microtomography, combined with broad character surveys of representatives of other trichomycterid genera, formed the basis for a redescription of R. totae and revealed the presence of four additional autapomorphies involving features of the cranium, autopalatine, and branchiostegal rays. This evidence further confirms the membership of Rhizosomichthys within the putatively non-monophyletic subfamily Trichomycterinae. We evaluate in R. totae the characters serving to diagnose the genera presently included in the Trichomycterinae.
Rhizosomichthys totae, el Pez Grasso, bagre gordo, o runcho del Lago de Tota, Colombia, es conocido de diez ejemplares y se piensa extinto. La especie es única entre los tricomictéridos en poseer marcados anillos de abundante tejido adiposo rodeando el cuerpo. Aunque su anatomía interna es conocida pobremente, la diagnosis de Rhizosomichthys totae y el estatus taxonómico no ha sido cuestionado dentro de Trichomycteridae. Reconstrucción osteológica no destructiva de un paratipo basado en microtomografía computada, combinada con un amplia búsqueda de caracteres en representantes de otros géneros de tricomictéridos, constituye la base para la redescripción de R. totae y revela la presencia de cuatro autopomorfías adicionales involucrando rasgos del cráneo, autopalatino, y radios branqulostegos. Esta evidencia además lo confirma como miembro de Rhizosomichthys dentro de la no monofilética subfamilia Trichomycterinae. En R. totae evaluamos los caracteres que sirven para diagnosis del género, actualmente incluido en los Trichomycterinae.
PYGIDIUM totae was described by Miles (1942) on the basis of four specimens from Lago de Tota, Colombia. Miles (1943) established the monotypic genus Rhizosomichthys for this distinctive trichomycterid, which can be readily distinguished from all other members of that family by the presence of six or seven rings of adipose tissue that encircle the trunk, plus two large pillows of adipose tissue on the posterodorsal aspect of the head (Fig. 1). This peculiar aggregation of adipose tissues on the head and body lend Rhizosomichthys a distinctive...