Comprehensive Description

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SciadesMüller & Troschel, 1849

(fig. 89)

SciadesMüller & Troschel, 1849: 6. Type species: Bagrus (Sciades) emphysetus ZBK Müller & Troschel, 1849. Type by subsequent designation. Type apparently designated first by Bleeker 1862: 8 (subgenus of Bagrus ZBK ). Gender: masculine.

Hexanematichthys ZBK Bleeker, 1858: 61, 126. Type species: Bagrus sondaicus ZBK Valenciennes, 1840. Type by monotypy. Gender: masculine.

Sciadeichthys ZBK Bleeker, 1858: 62, 66. Type species: Bagrus (Sciades) emphysetus ZBK Müller & Troschel, 1849. Type by monotypy. Gender: masculine.

Selenaspis ZBK Bleeker, 1858: 62. Type species: Silurus herzbergii ZBK Bloch, 1794. Type by subsequent designation by Jordan & Evermann (1896: 119). Gender: feminine.

Ariopsis ZBK Gill, 1861: 56. Type species: Arius milberti ZBK Valenciennes, 1840. Type by monotypy. Gender: feminine.

Leptarius ZBK Gill, 1863: 170. Type species: Leptarius dowii ZBK Gill, 1863. Type by monotypy. Gender: masculine.

FIGURE 89. Sciades emphysetus ZBK , USNM 215204, 193 mm TL. Lateral view.

Diagnosis. The species of Sciades can be differentiated from all other genera of the Ariidae by the combination of the following exclusive (1 to 5) and shared (6 to 8) characters: (1) medial groove of neurocranium delimited mostly or exclusively by frontal bones (fig. 90); (2) temporal fossa very reduced or entirely closed during ontogenetic development (fig. 90) (with exception of Sciades leptaspis ); (3) otic capsules little developed; (4) space between transcapular process and otic capsule very wide; (5) subvertebral process indistinct or little differentiated; (6) posterior cranial fontanel absent (fig. 90) (with exception of Sciades platypogon and shared with Batrachocephalus ZBK ); (7) epiphyseal bar indistinct (with exception of Sciades platypogon and shared with Batrachocephalus ZBK ); (8) exoccipital posterior process sutured to Muller’s ramus (with exception of Sciades platypogon and shared with Potamarius izabalensis ZBK ).

Supplementary morphological characters. Cephalic shield conspicuously granulated visible under the skin; lateral ethmoid and frontal limiting a small fenestra not visible under the skin; medial groove of neurocranium limited by frontal bones and/or on supraoccipital distinct or not very distinct; posterior cranial fontanel always closed (except in S. platypogon ); fenestra limited by supraoccipital, pterotic and sphenotic absent; fossa limited by pterotic, supracleithrum and extrascapular absent (except in S. leptaspis ); epioccipital not invading dorsal portion of cephalic shield; occipital process triangular, its length and width variable, progressively narrower toward its posterior part; anterior and median nuchal plates fused and indistinct, forming a structure of semi-lunar aspect or broad in form of shield; tooth plates associated with vomer round; accessory tooth plates large, oval shaped or subtriangular, bearing conical teeth; maxillary barbel fleshy and cylindrical; two pairs of mental barbels; base of adipose fin moderately long, about half as long as anal-fin base; lateral line not bifurcated at caudal region, reaching caudal-fin upper lobe (with exception of S. couma ); cleithrum wide, with second process on its upper portion; posterior cleithral process moderately long and distinct from dorsal process of cleithrum.

Remarks. Sciades contains the largest number of ariid species from the eastern and western Americas, south and southeast Asia, southern New Guinea and northern Australia. The nominal genera Hexanematichthys ZBK ,Selenaspis ZBK and Ariopsis ZBK represented by the respective type-species Pimelodus sagor ZBK Hamilton, 1822, Silurus herzbergii ZBK Bloch, 1794 and Arius milberti ZBK Valenciennes, 1840 (= Silurus felis ZBK Linnaeus, 1766), are considered junior synonyms of Sciades . The genus Sciades and Sciadeichthys ZBK are based on the same type-species, Bagrus (Sciades) emphysetus ZBK Müller & Troschel, 1849 and the latter is considered an objective synonym of the former. The osteology of Leptarius dowii ZBK Gill, 1863, the type-species of Leptarius ZBK , was not examined but morphological information from preserved specimens indicates that this genus is junior synonym of Sciades . In addition to S. mastersi (Ogilby, 1898), S. paucus (Kailola, 2000) and S. utarus (Kailola, 1990) were considered to belong in the genus based on the presence of external diagnostic morphological characters available in the literature. The inclusion of S. sona (Hamilton, 1822) is only tentative.

The species Sciades couma (Valenciennes, 1840), S. emphysetus ZBK , S. herzbergii ZBK , S. passany (Valenciennes, 1840) and S. proops (Valenciennes, 1840), form a subgroup well supported by the following exclusive characters, indicating that they might be considered a separate genus in future studies: lateral margin of premaxillary with a conspicuous concavity; mesopterygoid irregularly shaped (fig. 91); ectopterygoid very elongated (fig. 91); posterior nostrils connected by a groove (with exception of S. emphysetus ZBK and S. proops ).

Distribution and habitat. Eastern and western America, south and southeast Asia, southern New Guinea and northern Australia.

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