The caecilian order Gymnophiona is dominated by fossorial species with cylindrical bodies, compact skulls and reduced eyes suited to pushing through soil. The family Typhlonectidae broke from that pattern: its members are aquatic or semi-aquatic freshwater animals of South American river systems, and Potamotyphlus kaupii is among the most fully aquatic.
The body reflects the shift. Aquatic typhlonectids are laterally compressed rather than round in cross-section, and carry a low dorsal fin-like ridge toward the rear that aids undulatory swimming. Members of this family are viviparous, retaining young internally, and the young are nourished before birth rather than after hatching.
A related caution applies to the whole order. Caecilians are frequently reported as blind; the eyes are small and often covered by skin or bone, and vision is reduced to light detection at best, but the sensory tentacle between eye and nostril, unique to caecilians, does much of the work. Distribution and population data for most species, including this one, are thin.