Stijn Devaere

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

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.

Morphology of the cranial system of Platyclarias machadoi: interdependencies of skull flattening and suspensorial structure in Clariidae

The African catfish Platyclarias machadoi stands out from other clariid species by its extremely dorsoventrally flattened skull. This paper focuses on the spatial constraints and consequent functional interdependencies in this very low skull (average skull height of 27.5±3.0% skull length); such as the medial position of the retroarticular process on the lower jaw, the horizontal position of the suspensorium, the lateral tilting of the pterygoid bones and the anterior part of the quadrate with regard to the suspensorial transverse long axis. These characteristics can be presumed to have major influences on the capacity of suspensorial adduction, influencing the feeding and respiratory mechanisms. A comparison with other clariid species showed that one of the apomorphies is the presence of an extra muscle (musculus adductor mandibulae A3″ pars levator tendinis) in the adductor mandibulae complex. This extra muscle lifts the tendon complex of the adductor mandibulae, resulting in a higher moment on the lower jaw. Some comments on the original species/genus descriptions are given.

Redescription of Dolichallabes microphthalmus (Poll, 1942) (Siluriformes, Clariidae)

Abstract As a part of the general revision of anguilliform clariid genera and species, the status of Dolichallabes microphthalmus Poll, 1942, is reviewed, based on morphology and osteology of all available museum specimens. Dolichallabes microphthalmus, the most elongate species within the Clariidae, has been redescribed. Compared to Channallabes apus and Gymnallabes typus, D. microphthalmus is characterized by, in addition to some meristic differences, an elongate body, reduced skull ossification, with (1) one elongate fontanel, (2) antorbital and infraorbital IV the only circumorbital bones present, (3) only one or two suprapreopercular bones on each side, and (4) a sphenotic bearing only one process. Osteological evidence suggests that D. microphthalmus could be considered a paedomorphic clariid.

Morphology and spatial constraints in a dorso-ventrally flattened skull, with a revised species description of Platyallabes tihoni (Poll, 1944)

This study details the morphology of Platyallabes tihoni (Poll, 1944) as part of a complete revision of the anguilliform clariids. The overall body form of air‐breathing clariids ranges from fusiform to anguilliform genera (Boulenger 1911; Pellegrin 1927). Although P. tihoni has the typical external morphological features of other elongate clariids, this study shows that it occupies an intermediate position between fusiform and anguilliform taxa with regards to its cranial and postcranial morphology. The main morphological similarities of anguilliform species are a narrow skull roof with a high level of interdigitation between the bones, the reduced canal bones, a connection between the neurocranium and suspensorium via several processes, an extended tooth patch on the lower jaw, and the hypertrophied jaw muscle complex. Shared features typical for the fusiform species are a low coronoid process on the lower jaw and the posteroventral orientation of the opercular process on the hyomandibula. Platyallabes tihoni shows a series of unique features: an anterior fontanel situated entirely between the frontals, two tooth plates on the prevomer, a reduced height of the suspensorium, the absence of an anterior bony plate on the hyomandibula, a horizontal position of the sphenotic and pterotic, and a toothed entopterygoid. Many of these unique characters are linked to the spatial constraints associated with an extremely flattened skull in this species.