New heptapterid catfish described

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Scientists from Brazil and Argentina have described a new species of heptapterid catfish from northeastern Argentina.

The new species is named Rhamdella cainguae in a paper published by Flvio Bockmann and Amalia Miquelarena in a recent issue of the journal Zootaxa.

Rhamdella cainguae is distinguished from other members of the genus in having a distinct and large ovoid area in the supraorbital laterosensory canal between the frontal and sphenotic delimited by the apparently slender dorsal walls of these bones and with no foramen for a laterosensory branch. The new species is further distinguished from congeners by the following combination of characters: maxillary barbel reaching from the base of pectoral-fin ray to the posterior portion of the opercular region, eye diameter 20.6"23.9% head length, interorbital distance 17.9"20.7% head length, snout profile slightly convex, branchiostegal membranes not reaching the basal part of the first pectoral-fin ray in most specimens, 7 branchiostegal rays, interdorsal length 7.6"11.3% standard length, length of adipose-fin base 36.0"41.6% standard length, length of pelvic fin 13.3"16.9% standard length, length of anal-fin base 16.6"22.0% standard length, 16"18 (commonly 17) anal-fin rays, length of ventral caudal-fin lobe 55.8"65.5% of length of dorsal lobe, a dense concentration of long and slender papillae on the lateral body surface in the pectoral and abdominal regions, most conspicuous near the lateral line, and by the presence of a distinct narrow dark midlateral stripe.

The new species is known only from the Paran River drainage in northeastern Argentina, and its name comes from the Guaran: ca (forest) and igu (inhabitant), in allusion to the Caingu, and indigenous people of northeastern Argentina.

Rhamdella cainguae inhabits rocky bottoms in a clear water stream (ca. 50"100cm deep, with pools around 3m deep), running through a densely forested subtropical area. The species is gregarious, being densely grouped under large stones.

The study also describes the anatomy of the new species in detail, as well as assessing the phylogenetic relationships of Rhamdella to other heptapterids.

The composition of Rhamdella is also re-examined and only four other valid species in the genus are recognised: R. aymarae, R. eriarcha, R. longiuscula, and R. rusbyi.

For more information, see the paper: Bockmann, FA and AM Miquelarena (2008) Anatomy and phylogenetic relationships of a new catfish species from northeastern Argentina with comments on the phylogenetic relationships of the genus Rhamdella Eigenmann and Eigenmann 1888 (Siluriformes, Heptapteridae). Zootaxa 1480, pp. 1"54.