The serpent eel is an elongated slender fish, attaining a length of up to 250 cm (100 in), with a maximum diameter of 5 cm (2 in), although 100 cm (40 in) is a more common total length. The long, tapering snout has the upper jaw longer than the lower jaw. The teeth are sharply pointed and are normally visible; the front nostril is halfway between the tip of the snout and the eye, and the hind nostril is protected by a valve and concealed in a groove closer to the eye. The gape extends as far back as the eye, which has an almond-shaped pupil during the day and a circular pupil at night. The branchial opening is small, and is positioned just in front of the short pectoral fins. Both the dorsal fin and the anal fin are long and low, starting well behind the pectoral fins; there are no pelvic fins or tail fin, and the lateral line is clearly demarcated. The general colour is pale brownish-green, with dark punctuations on the snout and often with silvery reflections on the flanks; the belly is pale. Juvenile fish have a less elongated snout, and are a silvery colour.