Euchilichthys royauxi is a member of a family of African catfishes, the Mochokidae (Teleostei: Siluriformes). The family is better known for members of the genus Synodontis, which includes the well known upside-down catfishes. Euchilichthys and the two closely related genera, Atopochilus and Chiloglanis, are known as sucker-mouthed mochokids or suckermouths for their large ventrally directed oral discs. These sucker-mouthed genera have also been referred to as Chiloglanines, based loosely on a subfamily of the Mochokidae, the Chiloglanidinae (Riehl & Baensch, 1990).
Euchilichthys is a small genus with only 5 valid species from a total of 6 nominal forms. The closely allied genus Atopochilus has 7 valid species and a number of other nominal forms that were subsequently moved to Euchilichthys. The respective identity of these two genera is based largely on body form and tooth shape, but is questionable at best. Nonetheless, it seems likely that together they form a monophyletic group. The genus Chiloglanis, composed of what are typically smaller sucker-mouthed forms, is fairly diverse with about 50 species. The monophyly of this genus with respect to other mochokids is still untested; it is conceivable that it would be a paraphyletic group without including Euchilichthys and Atopochilus. It seems pretty clear, however, that Chiloglanines, as a group, are monophyletic.
Euchilichthys species can reach at least 55cm in total length and probably rival the largest Synodontis (at about 80cm). Species of Atopochilus (left) also reach large sizes, but it is unclear just how large (at least 25cm TL). Chiloglanis (right) species are much smaller, on the order of 10cm total length at their largest. The most notable feature of Chiloglanines is a ventrally directed oral disc. Further, Chilolglanines are characterized by depressed heads and skin covered in tubercles, especially near the head. Like some other mochokids, Chiloglanines are known to exhibit obvious sexual dimorphism. The most prevalent of these is dimorphism of the caudal fin, as seen in many Chiloglanis species such as the one pictured here. In males of various Chiloglanis species, the lobes of the caudal fin are elongated or differently shaped as compared to females (Roberts, 1989; Seegers, 1996). In Atopochilus savorgnani the anal fin of males is larger than that of females (personal observation).
Euchilichthys (and Atopochilus) are largely restricted to the Congo Basin, but spill over into neighboring rivers of western Africa. Chiloglanis has a broader distribution, similar to that seen in Synodontis (i.e., covering most of sub-Saharan Africa). All of the Chiloglanine genera inhabit rivers of central Africa and some Chiloglanis have invaded the rift lakes of eastern Africa. Not surprisingly, Chiloglanines are largely benthic, keeping to the bottom most of the time. Larger Euchilichthys and Atopochilus may be relatively solitary, but some smaller species (especially certain Chiloglanis species) are known to occur in great numbers when present. As far as known, there are no fossils attributable to the Chiloglanine genera.
The ecology of Euchilichthys and the other Chiloglanines is not well studied; the only information with regards to the ecology of these species pertains to diet. As with other mochokids, it is expected that most Chiloglanines are omnivorous. However, the levels of plant versus animal material in the diet vary widely (personal observation, Vigliotta). The diet of many Chiloglanis species seems typical of Synodontis; the gut usually contains a fair amount of sand, plant matter and detritus interspersed with larval insects, worms and other small invertebrates. In the larger Chiloglanines the gut is quite often filled by dark, fine grit, presumably silt or sand mixed with algae; it is much less common to find larger invertebrates in the guts of these species. In this respect Euchilichthys and Atopochilus are very likely the most herbivorous/detritivorous of the mochokids. At least twelve species of Chiloglanis and one species of Atopochilus have been listed as threatened on the IUCN red list.
The relationship of Euchilichthys to other mochokids is still unclear, though it seems likely that Chiloglanines, as a whole, represent a monophyletic group. Furthermore, as stated above, it seems likely that Euchilichthys and Atopochilus form a monophyletic group. All or most Chiloglanines are characterized by the following features, which can be seen in the images above and in this labeled image (left): sucker-like mouth incorporating trifurcate barbels into lower lip; mesethmoid entirely without anterolateral cornua; posterolateral corner of neurocranium greatly modified; 5 infraorbitals; enlarged premaxillary tooth plates; shortened palatine; posterior end of palatine without cartilage; ball-shaped condyle where hyomandibula meets the underside of the neurocranium; posterohyal flared distally; relatively straight mesocoracoid arch; absence of pectoral locking foramen; absence/reduction of serrae on the posterior edge of the pectoral spine; reduced number of dorsal rays; plate-shaped first anal fin pterygiophores; strut-like parapophysis of the 6th centrum; absence/reduced number of mandibular canal pores; and partially or greatly reduced gas bladder.
Mochocidae page on MongaBay.com
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