The morphology of prehatching embryos of Caecilia orientalis (Amphibia: Gymnophiona: Caeciliidae).

The state of development of advanced embryos of the direct-developing Ecuadorian caecilian Caecilia orientalis (Caeciliidae: Gymnophiona: Amphibia) was examined. Because it is established that development is correlated with reproductive modes in a number of features, we included comparison with taxa that represent the major reproductive modes and all of the modern normal tables and ossification sequences. The embryos of C. orientalis most closely resemble those of stage 47/48 Gegeneophis ramaswamii, an Indian caeciliid, and stage 47/48 Hypogeophis rostratus, a Seychellian caeciliid, both direct developers, in details of bone mineralization, chondrocranial degeneration, and vertebrogenesis. They are most like stage 45 H. rostratus in external features (gills, pigmentation, etc.). They are less similar to prehatchings of Ichthyophis kohtaoensis, an ichthyophiid with free-living larvae, and to fetuses of the viviparous caeciliid Dermophis mexicanus and the viviparous typhlonectid Typhlonectes compressicauda at comparable total lengths in both skeletal development and external features. The similarity of developmental features among the direct-developers suggests a correlation with mode of life history. A noteworthy feature is that C. orientalis has an armature of multiple rows of teeth on the lower jaw with tooth crowns that resemble the "fetal" teeth of viviparous taxa and that are covered with a layer of oral mucosal epithelium until full development and eruption, but the upper jaw bears a single row of widely spaced, elongate, slightly recurved teeth that resemble those of the adult.