CHARDON, Michel; PARMENTIER, Eric; VANDEWALLE, Pierre; DIOGO, Rui: Derived State of Weberian Characters in Loricarioids and Amphiliids

Modifications of the Weberian apparatus are exceptional. The pars inferior of the labyrinths and anterior Weberian ossicles are transformed in loricarioids and amphiliids only (Chardon, 1967; Jenkins, 1979: electron microscopy; Coburn and Grubach, 1997: development; de Pinna, 1998: discussion and amphiliids). A more in deep anatomical investigation is proposed. Loricarioids appear homogenous, with one difference however . The mesial processes of the exoccipitals are lost, so that the sinus impar is no longer separated from the nervous cord. The anterior end of the saccule and sagitta is lost and hence the origin of the canalis utriculo-saccularis seems to be displaced. In callichthyids and trichomycterids however, contrary to loricariids, part of the dorsal and lateral walls of the sinus impar is ossified and somehow mimicks an exoccipital bridge, but confusion is impossible: a medial suture is lacking and there is no connection with the exoccipitals. Nematogenyids, astroblepids and scolopacids have not been investigated. In both amphiliids subfamilies, Amphiliinae and Doumeinae, the exoccipital bridge is somewhat reduced so that the main part of the pars inferior is conspicuous in dorsal view after removing the brain. Only the anterior tip of the saccule and the very posterior part of the lagena are hidden under bone. The shape of the saccule and lagena is different from that in loricariids. De Pinna (1998) gives a figure of the exoccipital bridge in Amphilius pictus where the left and right wings do not meet completely, it is either an extreme case of reduction or the appearance of an alizarine preparation in which the collagen fibres joining the two wings are not conspicuous.