Bermejuela

Achondrostoma arcasii differs from other species in its genus by having between 40 and 45 scales in its lateral line; 4 or 5 scale rows are found between the lateral line and the origin of the pelvic fin; the caudal peduncle has 14 rows of scales around it; the diameter of the eye diameter is equal to or greater than the length of the snout, which is rounded and obtuse; and the ventral profile of head has no marked angle at the articulation of the lower jaw. The bermejuela has a maximum total length of 25 cm (9.8 in), although 15 cm (5.9 in) is more typical.

Achondrostoma arcasii is endemic to northeatsern Spain where it is found in rivers draining into the Mediterranean sea from the Francolí to the Túria, including the Ebro. The bermejuela is found in lakes and mountain streams, including the middle reaches of rivers. It can also occur in reservoirs in upland areas. The juveniles can be found in shallow stretches where there is a slow current and move to deeper and swifter stretches in late July.

Achondrostoma arcasii belongs to the genus Achondrostoma, this name places the prefix a-, meaning "without", in front of the genus name Chondrostoma, which is a combination of chondros, a word meaning "gristle" or "cartilage", with stoma, meaning "mouth". This is an allusion to the lack of the horny plates in the mouths of these fishes, which are present in Chondrostoma . The specific name, arcasii, honours Laureano Pérez Arcas, a Spanish zoologist who shared specimens with Steindachner.