Merendon Palm-pitviper

This is a medium-sized pitviper with a slender body and strong prehensile tail. Adults are usually 60–80 centimetres (24–31 in) long, with a maximum recorded length of 97 centimetres (38 in). It has 21–23 dorsal scale rows at mid-body. The head and body usually have a greenish dorsal color, shading to yellow-greenish along the sides. The belly is generally lighter in color: cream, yellow-green or pale green. The dorsal pattern may have irregular blotches, turquoise to black, or speckling that doesn't reach very far down the sides. The head has two black stripes and black speckling on top, which are less visible towards the tail. Like all other pitvipers, B. thalassinus has heat sensitive organs, or loreal pits, located on either side of the head between the eye and the nostril.

Its range extends from eastern Guatemala to western Honduras. In eastern Guatemala it is found in several mountain ranges, including Sierra de Caral in Izabal and the Sierra del Merendón in Zacapa.

Like other Bothriechis members, this species appears to be mainly nocturnal and arboreal. It preys mostly on frogs, lizards, and sometimes small mammals or birds. B. thalassinus is not known to be an aggressive species, but may strike quickly when surprised or disturbed.