American and Brazilian scientists have described a new species of herbivorous anostomid tetra from the Orinoco River drainage in Venezuela and Colombia.
The description of the new species, named Schizodon scotorhabdus, is published in the most recent issue of the journal Copeia in a paper by Brian Sidlauskas, Julio Garavello and Jennifer Jellen.
Schizodon scotorhabdotus can be distinguished from all other members of the genus except S. isognathus, S. knerii and S. nasutus in having a dark stripe along the lateral-line-scale row from the rear of the opercle to the caudal peduncle.
It differs from S. nasutus by its terminal or slightly upturned mouth, and from S. isognathus and S. knerii in having 4 or 4.5 transverse scale rows above the lateral line to the dorsal-fin orgin, 4 or 4.5 transverse scale rows below the lateral line to the anal-fin orgin and 7 branched anal-fin rays.
Schizodon scotorhabdotus further differs from S. isognathus in having three or four vertical dark blotches on the lateral surfaces of the body intersecting the lateral stripe and a terminal mouth in adults, and from S. knerii in having 16 circumpeduncular scales.
The new species (the name comes from the Greek scotos, meaning dark and rhabdos, meaning rod or stick, and refers to the prominent dark lateral stripe in this species) commonly occurs throughout the lowlands of the Orinoco River drainage, and shows a marked preference for lentic (still water) habitats.
The habitat preference is most likely due to its dietary preference for aquatic macrophytes that grow in slow, shallow water.
The mouth orientation in S. scotorhabdotus changes during growth, with young juveniles having a strongly upturned mouth (similar to adults of Laemolyta) and adults with a terminal mouth.
The study also redescribes S. isognathus, a morphologically similar species with which S. isognathus was previously misidentified.
For more information, see the paper: Sidlauskas, BL, JL Garavello and J Jellen (2007) A new Schizodon (Characiformes: Anostomidae) from the Ro Orinoco system, with a redescription of R. isognathus from the Ro Paraguay system. Copeia 2007, 711"725.