A COMPARATIVE-STUDY OF LOCOMOTION IN THE CAECILIANS DERMOPHIS-MEXICANUS AND TYPHLONECTES-NATANS (AMPHIBIA, GYMNOPHIONA)

We compared locomotion of two species of caecilian using x-ray videogr aphy of the animals ec traversing smooth-sided channels and a peg boar d. Two channel widths were used, a body width channel and a body width +20% channel. The terrestrial caecilian, Dermophis mexicanus, used in ternal concertina locomotion in both channels and lateral undulation o n the pegboard. The aquatic caecilian, Typhlonectes natans, was not ab le to move at all in the body width channel. In the wider channel Typh lonectes proceeded at the same speed as Dermophis while using normal, rather than internal, concertina locomotion. On the pegboard, Typhlone ctes used lateral undulation and achieved 2.5 times the speed managed by Dermophis. A phylogenetic analysis of this, and other, evidence sho ws that (1) internal concertina evolved in the ancestor to extant caec ilians and (2) internal concertina locomotion was secondarily lost in the aquatic caecilians. (C) 1997 The Linnean Society of London.