Amphiarius, Alexandre P. Marceniuk & Naércio A. Menezes, 2007

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 : 11-12

Amphiarius new genus

(fig. 8)

Type species: Arius rugispinis Valenciennes in Cuvier & Valenciennes, 1840b.

Diagnosis. Distinguished from the remaining ariid genera by the following exclusive (1) and shared (2) characters: (1) accessory tooth plates small to moderate roughly round and laterally located; (2) bony bridge formed by frontals and lateral ethmoid having frontals as its major component (shared with Cathorops , Cephalocassis and Hemiarius ).

Supplementary morphological characters. Cephalic shield granulated visible under the skin; a moderately developed fenestra limited by frontal and lateral ethmoid bones clearly visible under the skin; medial groove of neurocranium limited by frontal bones and/or on supraoccipital absent; posterior cranial fontanel oval, clearly differentiated; fenestra limited by supraoccipital, pterotic and sphenotic absent; fossa limited by pterotic, supracleithrum and extrascapular relatively large; epioccipital invading or not into dorsal portion of cephalic shield; occipital process funnel shaped long, its posterior part considerably narrower than its base; anterior and median nuchal plates fused, indistinct forming a structure of semi-lunar aspect; vomerine tooth plates absent; accessory tooth plates round to oval shaped, with acicular teeth; maxillary barbel fleshy and cylindrical; two pairs of mental barbels; base of adipose fin very long, as long as anal-fin base; lateral line not bifurcated at caudal region, reaching base of caudal-fin upper lobe; cleithrum wide, with a second dorsal process on its upper portion; posterior cleithral process moderately long and distinct from second dorsal process of cleithrum.

Remarks. Amphiarius phrygiatus and A. rugispinis were considered by Marceniuk (2003) as belonging to a monophyletic genus not formally described at that time, and Kailola (2004) suggested that the two species could represent a new genus. The two species were previously included in Arius by Taylor & Menezes (1977), Burgess (1989), Cervigón (1992), Le Bail et al. (2000), Camargo & Isaac (2001), Acero (2003), Marceniuk & Ferraris (2003), and in Notarius by Betancur & Acero (2004), but can be separated out from the former by the absence of medial groove on the cranium, lateral line not bifurcated at caudal region, reaching caudal-fin upper lobe and base of adipose fin as long as anal-fin base and from the latter by the absence of teeth associated with vomer and occipital process funnel shaped, long, its posterior part considerably narrower than its base (see also diagnosis of the genus).

Distribution and Habitat. North and eastern South America, marine, brackish and fresh waters.

Etymology. The first part of the generic name amphi is from Greek meaning on both sides, double, with reference to the occurrence of the included species both in fresh and marine waters. The second part is from the frequently used ariid generic name arius. Gender: masculine.