Cranial morphology of the anguilliform clariid Channallabes apus (Günther, 1873) (Teleostei: Siluriformes): are adaptations related to powerful biting?

Abstract Within the clariids (air‐breathing catfish), a complete range of fusiform to anguilliform species can be observed. This study deals with the cranial morphology of Channallabes apus , an extreme anguilliform (eel‐like) species, compared to the anguilliform Gymnallabes typus and the more fusiform Clarias gariepinus . The overall morphology of the head of Channallabes apus shows a hypertrophied adductor mandibulae complex, with the corresponding substantial narrowing of the neurocranium, seen in the frontals, the sphenotics, the pterotics and the posttemporo‐supracleithra, as well as the reduction and displacement of the eyes and some canal bones, such as the infraorbitals and the suprapreopercles. The presence of a hypertrophied muscle complex possibly indicates that a more powerful bite may occur. This implies that adaptations can be expected in several parts of the skull. On the lower jaw of C. apus a higher coronoid process is found, and on the suspensorium, two sets of three processes are present on the hyomandibular bone, indicating a stronger connection to the neurocranium. Several of the observed features, such as the elongation of the body, the reduction of the eyes, the increase in vertebrae number, limblessness and the increasing rigidity of the skull, may also be related to a process of miniaturization.