Comprehensive Description

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Arius ZBK Valenciennes, 1840

(fig. 9)

Arius ZBK Valenciennes in Cuvier & Valenciennes, 1840b: 53. Type species: Pimelodus arius ZBK Hamilton, 1822. Type by absolute tautonymy. Gender: masculine.

? AriodesMüller & Troschel, 1849: 9. Type species: Bagrus (Ariodes) arenarius ZBK Müller & Troschel, 1849. Type by subsequent designation. Type designated by Bleeker (1962: 8; 1863: 91) (subgenus of Bagrus ZBK ). Gender: masculine.

Pseudarius ZBK Bleeker, 1862: 8. Type species: Pimelodus arius ZBK Hamilton, 1822. Type by original designation. Gender: masculine.

Diagnosis. Arius ZBK species can be distinguished from all other ariid genera by the following combination of non-exclusive characters: (1) frontal bones without laminar mesial projection (shared with Amphiarius , Aspistor ZBK , Cathorops , Cephalocassis ZBK , Cryptarius ZBK , Doiichthys ZBK , Galeichthys ZBK , Hemiarius ZBK , Nedystoma ZBK , Nemapteryx ZBK , Osteogeneiosus ZBK , Potamarius ZBK and Potamosilurus latirostris ); (2) orbitosphenoid lateral projections moderately long, its lateral edge irregularly shaped (shared with Carlarius parkii ); (3) mesopterygoid subtriangular and very long [shared with Amphiarius rugispinis , Bagre (with exception of B. panamensis ), Cathorops , Cephalocassis ZBK , Cinetodus ZBK , Cryptarius ZBK , Doiichthys ZBK , Genidens ZBK , Hemiarius ZBK , Nedystoma ZBK , Nemapteryx ZBK , Pachyula ZBK , Potamarius ZBK , Sciades assimilis , S. leptaspis , S. guatemalensis , S. platypogon , S. sagor and S. seemanni ]; (4) third basibranchial cup shaped its anterior portion very wide, posterior portion elongated [shared with Amphiarius , Aspistor ZBK , Batrachocephalus ZBK , Cephalocassis borneensis , Cinetodus ZBK , Cryptarius ZBK , Hemiarius stormii , Netuma , Pachyula ZBK , Plicofollis ZBK (with exception of P. platystomus and P. tenuispinis ) and Sciades (with exception of S. bonillai , S. guatemalensis , S. proops , S. passany and S. sagor )].

Supplementary morphological characters. Cephalic shield granulated visible under the skin; fenestra of moderate size limited by frontal and lateral ethmoid bones visible under the skin; medial groove of neurocranium very distinct, limited by frontal bones and/or on supraoccipital; posterior cranial fontanel moderately large, long and narrow; fenestra limited by supraoccipital, pterotic and sphenotic bones absent; fossa limited by pterotic, supracleithrum and extrascapular relatively large; epioccipital not invading into dorsal portion of cephalic shield; occipital process triangular, moderately long and wide, progressively narrower toward its posterior part; anterior and median nuchal plates fused, indistinct forming a structure of semi-lunar aspect; vomerine tooth plates absent; accessory tooth plates present, oval shaped or longitudinally elongated, bearing conical or molar-like teeth; maxillary barbel fleshy, cylindrical; two pairs of mental barbels; base of adipose fin moderately long, about half length of anal-fin base; lateral line bifurcated at caudal region, reaching base of caudal-fin upper and lower lobes; 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. The limits and the monophyletic condition of Arius ZBK have always been one of the great challenges in ariid systematics. The genus was never properly defined and included most of the species currently considered to belong in different valid genera. The difficulties in the identification and composition of Arius ZBK have been recently emphasized by Kailola (1999) and Acero (2003) who recognized it as a non-monophyletic group . Two groups of species are herein distinguished: with accessory tooth plates very elongated bearing molar-like teeth (group one) and with accessory tooth plates oval shaped or subtriangular bearing acicular or conic teeth (group two). They are not named and the phylogenetic relationships within Arius ZBK will be fully discussed in another paper.

Although not examined, A. jella ZBK Day, 1877, A. malabaricus ZBK Day, 1877 and A. microcephalus ZBK Bleeker, 1855 are considered to belong in Arius ZBK (group one) based on presence of certain external morphological features described in the literature. The same is true for A. acutirostris ZBK (Day, 1877), A. africanusGünther , 1867, A. brunellii ZBK Zollezi, 1939, A. burmanicus ZBK Day, 1870, A. festinus ZBK Ng & Sparks, 2003, A. leptonotacanthus ZBK Bleeker, 1849, A. macronotacanthus ZBK Bleeker, 1846, A. nenga (Hamilton, 1822), A. oetik ZBK Bleeker, 1846, A. subrostratus ZBK Valenciennes, 1840, A. uncinatus ZBK Ng & Sparks, 2003, A. venosus ZBK Valenciennes, 1840 (group two). A. jatius (Hamilton, 1822) was not examined and although not having accessory tooth plates it was included in the genus based on the moderate size of its adipose fin and the lateral line bifurcated at the caudal region. As the other species of Arius ZBK its distribution is restricted to the Indian Ocean. No specimen of Bagrus arenarius ZBK Müller & Troschel, 1849 could be obtained for examination and descriptions available in the literature do not allow the recognition of the species as a member of Arius ZBK . Thus, the inclusion of A. arenarius ZBK in the genus is preliminary and based only on Kailola’s (2004) results. The recognition of Arenarius as junior synonym of Arius ZBK is tentative and needs confirmation.

Distribution and Habitat. Eastern Africa and south to southeast Asia, brackish and fresh waters.

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