Lake Taal Snake

Like all "true" sea snakes, H. semperi is a rather heavyset snake, elongated with a small head. It possesses the characteristic flattened, paddle-like tail found in the members of its subfamily. This particular species is considered short in comparison to the rest of the family; adult specimens of H. semperi that have been caught have a total length (including tail) of 50 to 70 cm (20 to 28 in). The snake is colored much like a typical sea snake, having a dark blue or black body with narrow yellow (sometimes white) crossbands. Like its close relatives, its nostrils are located almost dorsally, with valves that prevent water from entering its nasal (and oral) cavities when the snake is submerged.

H. semperi is known to be found only in the waters of Lake Taal (formerly known as Lake Bombon) in the province of Batangas in the Philippines. The only freshwater sea snake in the country, it lives the entirety of its life within the confines of the lake, feeding and breeding in its slightly acidic waters. The lake itself is a volcanic crater lake, which was formerly saltwater but gradually lost its salinity after the lake was closed off from the sea by an eruption in the 16th century. It is this unique aspect of the lake's formation and history that led to the evolution of several once-saltwater species, including H. semperi. Thus, this species is relatively young, having been accustomed to freshwater for less than a millennium.

As with "true" sea snakes, H. semperi is piscivorous, feeding primarily on the numerous fish species that are known to dwell in Taal Lake's murky waters.

H. semperi was named after Carl Semper, a German ecologist who discovered the species in the mid-19th century. Locally, the snake is known as duhol matapang.