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This article details the external morphological characteristics used in the identification of caecilians.

external morphology of the head of a caecilian

Close up of the head of Ichthyophis glutinosus (common yellow banded caecilian) preserved specimen from a museum.

Eyes -

The eyes are small and covered by skin (which is an adaptation to burrowing behaviour and a subterranean life). They can't see well but can perceive varying degrees of light. Some species have protrusible eyes and some lack eyes altogether. Thus eyes are an important characteristic that help identify the species.

Tentacles -

These are thought to be used as olfactory (smell) sensory organs in addition to the normal sense of smell that the nostrils are capable of. The tentacles are found between the eye and the nostril and their relative position (being closer to the eye or the nostril depending upon the species) as well as the relative length of the tentacles is important for identification.

Body Colouration -

Body colouration is useful in the identification of some species but as usual, colouration is not a characteristic that can solely be depended upon to distinguish between species.

Scales -

Some caecilians have small scales under their skin made up of calcite. The presence or absence of these and their shape (such as circular/cycloid) are important for identification.

Annuli -

The skin like folds running around the bodies of the caecilians make the body look segmented like an earthworm. The folds can be complete (called complete annuli) or incomplete (incomplete annuli). The annuli, whether they are complete or not, and the number of these present on the body of an individual are all important characteristics that help identify a species.

Body Colouration -

Body colouration does help with identification to an extent but should never be solely relied upon as there are man species that share similar colouration and many colour variations (called colour morphs) within the same species.

 

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References -

Boulenger, G. (1890). Reptilia and Batrachia. Publisher – Taylor and Francis (Original Publisher).