Macrhybopsis

Gilbert, Carter R., Mayden, Richard L. & Powers, Steven L., 2017, Morphological and genetic evolution in eastern populations of the Macrhybopsis aestivalis complex (Cypriniformes: Cyprinidae), with the descriptions of four new species, Zootaxa 4247 (5), pp. 501-555 : 508

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).