AUSTRALIAN BIODIVERSITY RECORD - Calodema

Australian Biodiversity Record, 2007 (8): 1-124Hydrophis bicolor maculata Jan, G. (1863). Elenco Sistematico Degli Ofidi. [p. 109] [?nomennudum].Hydrophis bicolor maculata Jan, G. and Sordelli, F. (1872). Iconographie Ophidiens. Atlas.[livr. 40, pl. 3 fig. 1]. Type data: syntypes (probable) MNHP 7710, MNHP 3975. Type locality:Indian Ocean.Description: Probably the most widespread as well as one of the most beautiful species ofsea snakes. This species can be immediately recognized by its bold colour pattern of blackdorsum and golden yellow venter - although there is considerable variation in colour andpatterning both between and within the different ‘populations’ across its range. In mostspecimens there is a clear mid-lateral line of demarcation between the dorsal and ventralcolour anteriorly, but on the posterior of the body and the tail, this line may become verywavy. The head is uniform black with the labials yellowish. The dorsal colouration varies fromone individual to another with some being purplish black, or uniform black, or even darkbrown. The ventral colour is more often yellow, but some can be brownish throughout theventer and this extends onto the lower lateral zone where it is separated from the darkdorsum colour by a narrow yellow line mid-laterally. The tail is a similar yellow to the venter,with the addition of a black barring pattern, and a lower ventro-lateral row dark spots orblotches - which may coalesce into a longer pattern in places. This unique colouration andpatterning suits a lay-and-wait predator, as the lighter yellowish ventral colour and darkbluish-black dorsum provides excellent camouflage amongst the yellowish-green and darkblue-black of drifting seaweeds that it lives amongst. Some of the more distinctive features ofthis species’ morphology are as follows: The head is rather long and deep, the body-form islong but robust, and is strongly compressed laterally. It can be immediately separated from allother genera by the following combination of characters: Head shields enlarged, symmetrical;preoculars 1-2 (mostly 1); postoculars 2-3 (mostly 2); primary temporals 2 or 3; supralabials6-8 (usually 7 or 8); 3rd supralabial contacting preocular; no distinct mental groove; bodyscales small and juxtaposed, either triangular or hexagonal in shape; body scales in 27-34rows at neck; body scales in 47-69 rows at mid-body (with females having a slightly highermid-body count than males); body scales at the ventro-lateral margin usually with 2 or 3 smalltubercles in mature specimens, and these appear to be slightly more prominent in males;ventrals about 240 to 406 (females have a higher ventral count than males); ventrals small(barely discernable from adjacent body scales), usually divided and about as wide as, or justwider than, adjacent body scales. There is a positive correlation between the number of midbodyscale rows and the number of ventrals that appears to have a developmental rather thanan ecological basis. It reaches a maximum size of about 0.85m. in total length, althoughspecimens around 1.1 metre in total length are known. Females tend to have a greater svlthan males, are sexually mature at around 63cm svl. Australian specimens also appear toreach a larger size than populations elsewhere in the world and when one also considers thedistinctive reproductive pattern in Australian waters, this may indicate that Pelamis platuruscould comprise more than one species. During the last 240 years since its originaldescription, a number of synonyms have been described, and numerous studies on otheraspects of its biology have appeared, but no adequate taxonomic revision has beenundertaken on the species across its entire range. A global-wide genetic and morphologicalstudy could reveal surprises that may enrich our understanding of the evolutionary history ofthis species as well as its relations with other proteroglyphic snakes. Research on thetaxonomy of Pelamis could also reveal new insights into other fields such as ecology,physiology and toxicology for instance that may have broader implications for ourunderstanding and conservation of marine ecosystems and their functioning. The taxonomy ofPelamis platurus would be an ideal project for an international research collaborationinvolving various universities and museums.Distribution: This species has the largest distribution of any sea snake, mainly occurringthroughout tropical and sub-tropical parts of both the Indian and Pacific Oceans, but not in theAtlantic Ocean. In Australia, it occurs widely throughout tropical, sub-tropical and onoccasions even in temperate waters, being found off the coasts of Queensland, NorthernTerritory and Western Australia, and on frequent occasions in New South Wales; it has beenonly rarely observed in the waters of Victoria and Tasmania. The species’ occurrence in57