120 Joseph Travis 



USE OF THE KEY 



This contribution should prove useful for live or preserved animals 

 in development stages 25 through 40 (Gosner 1960). The key is not 

 arranged phylogenetically. General arrangement and terminology follow 

 Altig's. 



Altig discussed some of the major sources of difficulty in tadpole 

 identification, beginning with the problem of poor preservation. Colora- 

 tion, useful in identifying live material, will fade in preserved specimens. 

 Labial teeth can fall out, and keratinized skin layers can be dislodged 

 from their underlying structures. 



Larval anurans are highly susceptible to environmental influences 

 on morphology. For example, food type can affect mouthpart mor- 

 phology, causing some distortions of the normal appearance, as is evi- 

 dent in a comparison of laboratory-reared and field-collected tadpoles. 

 Ambient temperatures will affect development rates, and may influence 

 allometric growth patterns (see below). The tails of many tadpoles are 

 damaged by predators, particularly nymphal dragonflies (Caldwell et al. 

 1980). This may affect comparisons based on length ratios, either 

 because of the tail's abbreviated length or because of a change in its 

 overall shape as regeneration occurs. In addition, a regenerated tail 

 often has a blackened tip or large blotches or large blotches on the fin, 

 marks that may not be part of the normal pattern. Color of a live 

 animal can vary with background. Rana clamitans larvae developing in 

 a pond that contains a high level of gray clay in suspension (as in some 

 ponds in the Sandhills region) will be very pale, while larvae in other 

 situations may range from green to dark brown. 



Many characters vary ontogenetically. The most obvious of these is 

 color. The clear belly of young Rana clamitans larvae will become an 

 opaque, cream color as the animals develop. The number of rows of 

 labial teeth and the length of the rows change with tadpole age and size. 

 The most subtle ontogenetic variations are the allometric shape changes 

 exhibited by some species. The notable flagellum of a Hyla femoralis 

 tadpole is not present in a young larva, but becomes increasingly well 

 developed as the tadpole grows. Many species with broad fins, like Hyla 

 gratiosa and H. chrysoscelis, have more streamlined profiles as small 

 larvae. All these sources of phenotypic variation should be kept in mind 

 when using any key to tadpoles. 



