sea snakes

Rasmussen, Arne Redsted, Sanders, Kate Laura, Guinea, Michael L. & Amey, Andrew P., 2014, Sea snakes in Australian waters (Serpentes: subfamilies Hydrophiinae and Laticaudinae) - a review with an updated identification key, Zootaxa 3869 (4), pp. 351-371 : 357

Identification key to Australian sea snakes including 4 possibly

Identifying sea snakes to species level is not an easy task. The genus Hydrophis in particular shows great interspecific and intraspecific variation and interspecific convergence making identification problematic when using only external characters. The key is based primarily on counting ventral scales and scale rows around the neck and body, but shape and size of the head and the position of the maxillary bone are other distinguishing characters.

A combination of characters are required to identify a specimen. In using the key it is important that all the identifying characters fit with the specimen at each step in the key. If this is not the case, the alternative “not as above” should be followed. When counting scale rows around the neck and body it is important to note that the count around the neck is a minimum count and the count around the body is a maximum count (as in Smith, 1926). Record the minimum count of three or four scale rows around the neck at one and a half head lengths, two, two and a half, and three head lengths behind the head. The maximum number of body scales occurs just behind midbody, but three to four counts between midbody and vent are required. The most precise scale row count follows a transverse line across the dorsal surface of the body starting from a ventral scale to a ventral scale on the other side of the body (Thomas, 1976). Ventral scales are excluded from the count of scale rows. “Ground colour” refers to the colour between the darker dorsal markings or bands (if present), and is generally the same as the colour on the ventral side. “Bands” here refers to darkish transverse markings anywhere on the body. Drawings are by Mogens Andersen ZMUC. The nomenclature follows Sanders, Lee, et al. (2013).

1.

A Nasals separated by internasals (fig.1 left)........................................................... Laticauda

B Nasals not separated by internasals (fig.1 right)............................................................. 2.

2.

A Three supralabials, the second very elongated (fig.2 left).................................. Emydocephalus annulatus

B More than four supralabials (fig.2 right)................................................................... 3.

3.

A No preocular scale, the prefrontal borders the eye (fig.3 left)................................. Hydrelaps darwiniensis

B Preocular scales present (fig.3 right)...................................................................... 4.

4.

A Ventrals small, each not more than 2 times as broad as adjacent body scales.............................................................................................. Hydrophis and Microcephalophis (21 species—key below)

B Ventrals large, each at least 3 times as broad as adjacent body scales............................................ 5.

5.

A At least 28 scale rows around body...................................................... Parahydrophis mertoni

B Less than 28 scale rows around body:..................................................................... 6.

6.

A Maxillary bone not extending forwards as far as palatine (fig.4 left)................................ Ephalophis greyae

B Maxillary bone and palatine straight, or maxillary bone reaching beyond palatine (fig.4 right)................................................................................................... Aipysurus (8 species—key below)