Genus Macrhybopsis

Macrhybopsis Cockerell & Allison 1909: 162 (as subgenus of Hybopsis; type species Gobio gelidus Girard 1856, by original designation).

Extrarius Jordan 1919: 342 (type species Hybopsis tetranemus Gilbert 1886, by original designation [also monotypic]).

Macrhybopsis was proposed by Cockerell & Allison (1909), based on aspects of scale morphology. Although poorly founded, the genus received recognition because the type species ( gelida) is characterized most prominently by a single pair of maxillary barbels, and was accordingly placed by Hubbs & Ortenburger (1929: 25) in the “ Hybopsis complex” of North American minnows. Jordan (1919) meanwhile had erected a new genus, Extrarius, for reception of a single species ( tetranema) distinguished by the consistent presence of a second pair of maxillary barbels. Hubbs & Ortenburger (1929), in their description of another new and closely related four-barbeled species ( australis), determined that these two species bear a close relationship to another widespread two-barbeled species then known as Hybopsis aestivalis . They accordingly referred all three species to Extrarius, in which genus they remained until it was submerged by Bailey (1951: 192) into the broad genus Hybopsis, an artificial assemblage of North American cyprinids for which all included species possess one or two pairs of maxillary barbels. This arrangement remained largely unchanged until Extrarius was restored to a genus by Mayden (1989), to include the aestivalis species complex. Mayden (1989) also accorded recognition to Macrhybopsis, which comprised a clade including M. storeriana, M. gelida, and M. meeki; and considered it most closely related to the monophyletic genus Extrarius .

Coburn & Cavender (1992: 349), in their phylogenetic treatment of North American cyprinid genera, included 16 North American genera in a group termed by them the “chub clade,” within which nine (including Macrhybopsis) were included in the so-called “exoglossin clade.” Extrarius aestivalis was formally included within Macrhybopsis (Coburn & Cavender 1992: 354) based on six shared synapomorphies, including an enlarged nasal capsule; metapterygoid with an enlarged prong for insertion of the adductor palatine muscle; urohyal with an eroded horizontal lamina and a serrate vertical lamina; an elongated hyoid bar; a short triangular basihyal; and elongated branchiostegal rays. This assignment was accepted by Mayden et al. (1992), and is generally followed today.

As presently conceived Macrhybopsis comprises 12 species, including M. storeriana (Kirtland), M. gelida (Girard), M. meeki (Jordan & Evermann), and the nine species now recognized in the Macrhybopsis aestivalis species complex. The following generic diagnosis is copied verbatim from Boschung & Mayden (2004: 206): Body elongate, relatively slender; head flattened ventrally, snout conical to blunt. One or two barbels at corner of each jaw. Lateral scale rows 34 to 50; predorsal scales 14 to 24. Anal rays 7 or 8; pectoral rays 13 to 18. Pharyngeal teeth 1,4-4,1 or 4-4, or combinations thereof. Nuptial tubercles on pectoral fins. Enlarged nasal capsule. Elongated branchiostegal rays. Coloration dusky to silvery, with no chromatic pigments.

In species of the genus, tastebuds and lateral-line neuromasts are exceedingly abundant, and the eyes range from quite small (in M. gelida and M. meeki) to what could be described as “normal” in size. These senses working together account for their ability to occupy both clear and turbid waters (Branson 1963, 1975; Davis & Miller 1967; Reno 1969).