I’ve now had a chance to read the paper on Corydoras urucu.
Recently during ichthyological surveys in the Rio Urucu system, a right-bank tributary of Rio Solimões, specimens of a species of Corydoras were collected that appeared to be similar to several species that have an arc-like stripe (i.e., C. arcuatus, C. narcissus, and C. gracilis). Examination of the material revealed that this is a new species of Corydoras, which is described herein.
This is within the general distribution area of C. arcuatus although none have been collected there.
All specimens of Corydoras urucu were collected along semilentic stretches of the shore of the Igarape da Onca. The Igarape da Onca is a moderately large stream, about 15 m wide, with sand, clay, and leaves on the bottom, in addition to emerged vegetation. It has an average depth of 1 m during the dry season, and 4 m in the rainy season.
Very typical corydoras habitat. The holotype collection point is given as 4°52’9.12”S, 65°18’3.6”W.
Morphometric and meristic data show clearly this is a species very different from C. arcuatus in all respects apart from the arched body pattern. The only photograph is of a preserved specimen and this shows a body shape similar to that of C. griseus or C. bondi. Not as high-backed as C. arcuatus and with a blunt face. The eye is also relatively larger.
It appears to be a smaller species than C. arcuatus with the collected specimens having a mean standard length of just 24.2mm and the largest specimen having a standard length of 27.4mm. The authors are at pains to point out several differences between the new species and juvenile specimens of C. arcuatus which it otherwise resembles.
Although the evidence assigns the non-monophyly of an arc-striped group of Corydoras, it is premature to pinpoint the sister-group of Corydoras urucu. The inclusion of Corydoras urucu in Britto’s (2003) data matrix recovered it in a large polytomy, outside of clade VIII in that study (a group composed of C. arcuatus and C. gracilis, among other species of Corydoras).
The authors here make the case for the independent evolution of the arched markings of C. urucu although they are unwilling to speculate as to the actual relationship with other corydoras species which is somewhat disappointing although understandable. It’s always better to say “we’re not sure” than to publish an inaccurate supposition.
Etymology — “urucu” is from the type locality, the Rio Urucu basin.
The full paper can be downloaded from Copeia. (Subscription required)