Jansenii / Oxycephalum
by Freight Freitas
There has been some recent taxonomic debate leading to the addition of other species to the genus Gonyosoma including: G. cantoris, G. frenata, and G. hodgsoni, all formerly genus Elaphe (Schulz 1996). All of my personal experience is with G. oxycephala and G. janseni, and they are the focus of this website.
G. oxycephala: The name oxycephala can be literally translated to pointed head (oxus=sharp/pointed, and cephala=head), referring to the general head morphology of this species (Smith, year unknown). Typically known as either the red tailed green ratsnake, or racer, the common body coloration is emerald green with a distinct color change in the ventral region leading to a reddish, or silvery tail. There is often a distinct yet marginally undefined yellow band around the ventral region separating the body coloration from the tail coloration. Located laterally on the head is typically a faint black horizontal line that extends from the nose through the center of the eye and to the back of back of the jaw. This line separates the dorsal green head coloration from the yellow, pale green, or whitish ventral head coloration. The ventral scales are typically pale green back to the yellow ventral band. The tongue is black in the center with blue lateral stripes along the entire length of the black core. Its body is slender and delicate, and its head is very geometric with flat surfaces dorsally, ventrally, and laterally.
There are a number of color morphs in this species, which appear as regional varieties. Totally yellow specimens have been reported from Thailand and the Philippines, while numerous variations of the gray Java morph have been reported. Some Javanese specimens have an entirely gray body, which appears as an extension of tail coloration throughout almost the entire snake. Typically the head coloration will be much like the more common green morph with distinct dorsal green and ventral yellow head coloration. Variations to the gray morph include a base coloration of gray with a wash of some muted form of red, orange, yellow, or reddish brown over the otherwise gray scales. I personally have one snake that has gray at the extreme base of the scales, which transitions sharply into various shades of orange. Some of the color morphs have what appears as random spots or blotches of color that contrast the base coloration, and many possess three or more colors throughout their bodies. Babies typically hatch with a muted form of what will be their adult coloration, where janseni are green at hatching and experience a color metamorphosis to attain adult coloration.
G. oxycephala is a slender snake that is highly adapted to an arboreal lifestyle. Its prehensile tail is well adapted for holding onto vegetation, and it is highly adept at tying knots, that from my experience are very difficult to untie. Females are generally larger than males, and adult length is typically around 6ft, with an occasional individual reaching up to 7.5ft. The mouth can be opened 180°, and can inflict a large and initially painful bite. Though overall damage from such a bite is usually minimal, there can be excessive bleeding incurred from numerous extremely sharp teeth.
G. janseni: There are two color variants in this species, one being the black tailed janseni from Sulawesi, and the other being the black variety from Salayar. The black tailed Sulawesi (Celebes) janseni has a distinct body color change from a light anterior of bone white, tan, or gold, to a chocolate black posterior. The color transition is typically in the mid-body region, but can be more anterior or posterior in specific individuals. The transition can occur as diagonal bands, speckling, or longitudinal stripes of chocolate black that are typically faint, muted, or scattered at the anterior most region of transition. These areas then darken and condense into a solid black tail. The black tailed janseni is a much more heavily bodied snake than both the oxycephala and the black janseni, and is considered to be semi-terrestrial/semi-arboreal. The head in the Sulawesi variant appears heavier and more rounded than both the oxycephala and the black janseni. Babies are typically some shade of green (hunter, sea, emerald green) at hatching and tend to have faint diagonal black bands located laterally along the body. A metamorphosis to adult coloration occurs between 6-18 months of age in both janseni forms.
The black Salayar janseni is much more reminiscent of G. oxycephala than the Sulawesi black tailed janseni. Its body is slender and delicate, and its head is very geometric and flat dorsally, ventrally, and laterally making it almost identical to G. oxycephala in gross morphology. Body coloration is entirely chocolate black with occasional white in the lower lip and chin region. Like G. oxycephala this snake appears well adapted for an arboreal existence. To date I have found no literature relating to the black janseni, which raises the question; Is this truly a janseni, or another morph of the oxycephala?