A head with a suckermouth: a functional-morphological study of the head of the suckermouth armoured catfish Ancistrus cf. triradiatus (Loricariidae, Siluriformes)

The neotropical loricariid catfishes are highly specialized for adhering to substrates, and can continue breathing and even scrape food from these surfaces while using the mouth for suction. A detailed study integrating bones, muscles and ligaments was performed on Ancistrus cf. triradiatus, using cleared and stained specimens, dissections and manipulations on fresh specimens, serial sections, and histological examination of key tissues. A limited kinematic study using high-speed video was performed as well. The suspensorium is a rather rigid structure; the hyoid is more movable and associated muscles are more substantial; it appears to be more important in the buccal pump system. The transverse orientation of the hyohyoideus abductor suggests it can't open the branchiostegal membrane. This movement might be passive. Apart from divisions inserting on the lower and upper jaws, a medial adductor mandibulae division, the retractor veli, inserts on the oral valve. The retractor tentaculi(1) and the lateral part of the completely subdivided extensor tentaculi move the maxillary barbel, a structure that allows controlled inspiration preventing failing of the suction system. Rotational movements of the lower and upper jaws result in scraping the substrate. Antagonistic muscles for the adductor mandibulae divisions inserting on the lower and upper jaws might be a part of the protractor hyoidei and the medial part of the extensor tentaculi. The lower jaws are most mobile, not being linked to the hyoid arch medially. A medial cartilage plug acts as a supporting and gliding device for the lower jaws.