Comprehensive DescriptionRead full entry
Diagnosis. The presence of one exclusive (1) and twelve (2 to 13) shared characters define and distinguishes Cephalocassis ZBK from all other ariid genera: (1) presence of a fenestra between supraoccipital, pterotic and sphenotic (fig. 37); (2) mesethmoid very thin at median portion (fig. 37) [shared with Arius ZBK (with the exception of A. caelatus ZBK and A. madagascariensis ZBK ), Cathorops , Cinetodus ZBK , Ketengus ZBK , Osteogeneiosus ZBK , Pachyula ZBK and Potamarius ZBK ]; (3) vomer anterior margin acute and very conspicuous [shared with Amphiarius , Arius ZBK , Aspistor ZBK , Cinetodus ZBK , Potamarius ZBK , Osteogeneiosus ZBK , Plicofollis ZBK , Notarius ZBK (with exception of N. planiceps ), Pachyula ZBK and Potamosilurus macrorhynchus ]; (4) bony bridge formed by frontals and lateral ethmoid having frontals as its major component (fig. 37) (shared with Amphiarius , Cathorops and Hemiarius ZBK ); (5) contact face of transcapular process with basioccipital restricted and columnar [shared with Arius ZBK (with exception of A. gagora , A. maculatus ZBK and A. manillensis ZBK ), Batrachocephalus ZBK , Brustiarius ZBK , Carlarius , Cinetodus ZBK , Cochlefelis ZBK , Galeichthys ZBK , Genidens ZBK , Hemiarius ZBK , Ketengus ZBK , Neoarius ZBK , Netuma , Osteogeneiosus ZBK , Pachyula ZBK , Plicofollis ZBK (with exception ofP. platystomus ), Potamarius ZBK , Potamosilurus (with exception of P. latirostris ) and Sciades ]; (6) dentary teeth restricted to 2/3 of the mesial portion of the bone (shared with Cryptarius ZBK and Genidens ZBK ); (7) premaxilla narrow, almost as long as wide (shared with Cathorops , Cinetodus ZBK and Potamarius ZBK ); (8) metapterygoid 1.5 times longer than higher (fig. 38) [shared with Cathorops (with exception of Cathorops dasycephalus ), Cinetodus ZBK , Cryptarius ZBK , Pachyula ZBK , Plicofollis ZBK and Potamarius ZBK ]; (9) lower crest of hyomandibular absent (fig. 38) (shared with Cathorops and Ketengus ZBK ); (10) anterior portion of second basibranchial cup shaped and moderately differentiated (shared with Bagre , Batrachocephalus ZBK , Brustiarius ZBK , Cinetodus ZBK , Cochlefelis ZBK , Cryptarius ZBK , Galeichthys ZBK , Genidens ZBK , Neoarius ZBK , Pachyula ZBK , Potamarius ZBK and Potamosilurus latirostris ); (11) posterior portion of second basibranchial moderately long and thin [shared with Arius ZBK (with exception of A. gagora and A. maculatus ZBK ), Batrachocephalus ZBK , Cathorops , Notarius ZBK , Osteogeneiosus ZBK , Potamosilurus (with exception of P. latirostris ) and Sciades ]; (12) accessory crest connecting transversal and median crests of neural spine of fourth vertebra present (shared with Amphiarius , Aspistor ZBK and Notarius ZBK ); (13) base of adipose fin very long, as long as anal-fin base (shared with Amphiarius , Aspistor ZBK , Cinetodus ZBK , Galeichthys ZBK , Hemiarius ZBK , Notarius ZBK and Pachyula ZBK ).
FIGURE 36. Cephalocassis melanochir , USNM 230311, 229 mm TL. Lateral view.
Supplementary external characters. Cephalic shield granulated, visible under the skin; lateral ethmoid and frontal limiting a wide fenestra very conspicuous under the skin; medial groove of neurocranium limited by frontal bones and/or on supraoccipital absent; posterior cranial fontanel well differentiated, large and oval; fenestra limited by supraoccipital, pterotic and sphenotic present; fossa limited by pterotic, supracleithrum and extrascapular present or absent; epioccipital not invading dorsal portion of cephalic shield; shape of occipital process varying considerably; anterior and median nuchal plates fused and indistinct forming a structure of semi-lunar aspect; tooth plates associated with vomer absent; accessory tooth plates present or absent, when present bearing conical 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 bifurcated or not at caudal region, reaching base of upper and sometimes of lower caudal-fin lobes; cleithrum thin with second dorsal process located at its upper portion; posterior cleithral process short and distinct from second dorsal process of cleithrum.
Remarks. Examination of Pimelodus borneensis ZBK Bleeker, 1851, type-species of Hemipimelodus ZBK indicated that this genus is synonym of Cephalocassis ZBK . Since the two generic names were proposed simultaneously, we here consider Cephalocassis ZBK as the valid generic name. The inclusion of C. bleekeri (Popta, 1900) and C. manillensis (Valenciennes, 1840) is also tentative and based on a few external supplementary morphological characters from the literature and distribution of the species and needs confirmation.
Distribution and habitat. South and southeast Asia, freshwaters.