Potamarius

Alexandre P. Marceniuk & Naércio A. Menezes, 2007, Systematics of the family Ariidae (Ostariophysi, Siluriformes), with a redefinition of the genera., Zootaxa 1416, pp. 1-126 : 96-98

Potamarius Hubbs & Miller, 1960

(Fig. 84)

Potamarius Hubbs & Miller, 1960: 101. Type species: Conorhynchos nelsoni Evermann & Goldsborough, 1902. Type by original designation. Gender: masculine.

Diagnosis. The following combination of exclusive (1 to 3) and shared (4 to 14) characters distinguishes Potamarius from the remaining ariid genera: (1) optic foramen very large; (2) interopercle subrectangular (fig. 85); (3) lateral processes of urohyal completely free from bony blade contacting medial process of the bone (fig. 86); (4) mesethmoid median portion thin (fig. 87) [shared with Arius (with exception of A. caelatus and A. madagascariensis ), Cathorops , Cephalocassis , Cinetodus , Ketengus , Osteogeneiosus and Pachyula ]; (5) lateral horn of lateral ethmoid very long and pointing backward (fig. 87) [shared with Arius (with exception of Arius caelatus ), Doiichthys and Plicofollis (with exception of P. platystomus and Plicofollis tenuispinis )]; (6) anterior portion of vomer acute and conspicuous [shared with Amphiarius , Arius , Aspistor , Cephalocassis , Cinetodus , Osteogeneiosus , Plicofollis , Notarius (with exception of N. planiceps ), Pachyula and Potamosilurus macrorhynchus ]; (7) vomerine tooth plate absent [shared with Amphiarius , Arius , Batrachocephalus , Carlarius , Cathorops (with exception of C. dasycephalus ), Cephalocassis , Cinetodus , Cryptarius , Doiichthys , Genidens genidens , Ketengus , Nedystoma , Osteogeneiosus , Pachyula , Plicofollis platystomus and Potamosilurus velutinus ]; (8) frontal bones without mesial laminar projection (fig. 87) (shared with Amphiarius , Arius , Aspistor , Cathorops , Cephalocassis , Cryptarius , Doiichthys , Galeichthys , Hemiarius , Nedystoma , Nemapteryx , Osteogeneiosus and Potamosilurus latirostris ); (9) orbitosphenoid without lateral expansion [shared with Amphiarius , Aspistor , Bagre , Batrachocephalus , Cathorops , Cephalocassis , Cochlefelis , Cryptarius , Doiichthys , Galeichthys , Hemiarius , Ketengus , Nedystoma , Nemapteryx , Neoarius , Osteogeneiosus , Notarius (with exception of N. planiceps ), Pachyula , Plicofollis platystomus , Potamosilurus latirostris , Sciades couma , S. emphysetus , S. passany , S. proops , S. seemanni and S. sagor ]; (10) parasphenoid wing-like process absent (shared with Batrachocephalus , Cephalocassis , Cryptarius , Doiichthys , Ketengus , Nedystoma , Nemapteryx and Osteogeneiosus ); (11) premaxillary almost as long as wide (shared with Cathorops , Cephalocassis and Cinetodus ); (12) metapterygoid 1.5 times as long as high [shared with Cathorops (with exception of Cathorops dasycephalus ), Cephalocassis , Cinetodus , Cryptarius , Pachyula and Plicofollis ]; (13) metapterygoid anterior process truncate [shared with Cinetodus , Cochlefelis , Pachyula , Plicofollis and Potamosilurus (with exception of P. velutinus )]; (14) distance from optic foramen and trigeminofacial complex equal to width of complex (shared with Bagre and Galeichthys ); (15) third basibranchial in form of a long and thin hourglass (shared with Cochlefelis and Galeichthys ); (16) number of ribs equal to or less than 14 (shared with Amphiarius , Arius , Aspistor , Batrachocephalus , Brustiarius , Cathorops , Cephalocassis , Cinetodus , Cryptarius , Doiichthys , Galeichthys , Hemiarius , Ketengus , Nedystoma , Nemapteryx , Osteogeneiosus , Pachyula , Plicofollis platystomus and Potamosilurus ).

Supplementary morphological characters. Cephalic shield granulated visible under the skin; a moderately developed fenestra limited by lateral ethmoid and frontal visible under the skin; medial groove of neurocranium very distinct, limited by frontal bones and/or on supraoccipital; posterior cranial fontanel moderately developed, long and narrow; fenestra limited by supraoccipital, pterotic and sphenotic absent; fossa limited by pterotic, supracleithrum and extrascapular relatively large; epioccipital not invading dorsal portion of cephalic shield; occipital process triangular, moderately long and wide, progressively narrower toward its posterior part; anterior and median nuchal plates fused and indistinct, forming a structure of semi-lunar aspect; tooth plates associated with vomer absent; accessory tooth plates absent or rudimentary; maxillary barbel fleshy and cylindrical; base of adipose fin moderately long, about half as long as anal-fin base; lateral line not bifurcated at caudal region, reaching base of caudal-fin upper lobe; cleithrum wide, with second dorsal process on its upper portion; posterior cleithral process of moderate length, distinct from second dorsal process of cleithrum.

Remarks. The type-species of the genus, Conorhynchos nelsoni Evermann & Goldsborough, 1902 was characterized on the basis of characters observed in preserved specimens and data from the literature.

Distribution and habitat. Central and South America, freshwater.