Ontogeny of the Weberian Apparatus in the Armored Catfish Corydoras paleatus (Siluriformes: Callichthyidae)

Abstract

The ontogeny of the Weberian apparatus was studied from hatching to 21 days in larval and juvenile Corydoras paleatus and compared with the developing apparatus of ictalurids. By counting myoseptae, we determined that the complex vertebra of C. paleatus consists of only three fused vertebrae, which we infer are V3-5. Absent are VI and V2 and all their derivatives (claustrum, scaphium, intercalarium, centra) and two occipital myoseptae that are present in ictalurids. Also lacking are the cartilage elements of V3 and V4 that are characteristic of the typical siluriform Weberian apparatus including basidorsals, basiventrals, and supraneural 3. In contrast to previous studies, we found no evidence of neural arches 3 and 4, the rib + parapophysis of V4, or the os suspensorium. The sole Weberian ossicle (improperly called the compound tripus-scaphium) forms from an ossification of the paravertebral sac and the dorsal myoseptum of V3 and is referred to here as a myoseptal tripus. Basidorsals and basiventrals of V5 are present, and neural arch 5 contacts the occipital cartilage by three days posthatch. The bony encapsulations of the bipartite swimbladder are initiated as ossifications of the myoseptae of V5 posteriorly and peritoneal connective tissue ventrally and anteriorly.