Within the Gymnophiona (caecilians) oviparous species with biphasic life-cycles possess a free living semi-aquatic larval stage that feeds in aquatic habitats. The larvae pass through a metamorphosis to a purely terrestrial adult stage. It is likely that the cranial morphology of caecilian larvae has specializations for aquatic feeding. However, little is known about the cranial morphology, and the cranial musculature is especially neglected in the literature. This study provides a detailed description of the jaw and hyobranchial musculature in larval stages of a caecilian. We studied late embryonic and early larval specimens of Ichthyophis kohtaoensis. Furthermore, we compared and homologized the cranial muscles found in larval I. kohtaoensis with the muscles described for adult caecilians. Most cranial muscles of larval I. kohtaoensis are also present in the adult, except for the m. levator mandibulae externus and the m. subarcualis obliquus II. Our results were compared with the data available for larval frogs and salamanders in order to hypothesize the cranial musculature in the larva of the most recent common ancestor of the Lissamphibia. Larval caecilians, frog tadpoles, and salamander larvae share many characters in their cranial musculature, which, consequently, can be assigned to the lissamphibian ground pattern. However, the m. pterygoideus and the m. levator quadrati are unique to the Gymnophiona.
