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''Emydocephalus annulatus'', commonly known as the turtleheaded sea snake or egg-eating sea snake, is a
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of
sea snake Sea snakes, or coral reef snakes, are elapid snakes that inhabit marine environments for most or all of their lives. They belong to two subfamilies, Hydrophiinae and Laticaudinae. Hydrophiinae also includes Australasian terrestrial snakes, wher ...
that can be found in waters of
Oceania Oceania (, , ) is a region, geographical region that includes Australasia, Melanesia, Micronesia, and Polynesia. Spanning the Eastern Hemisphere, Eastern and Western Hemisphere, Western hemispheres, Oceania is estimated to have a land area of ...
near
Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
and some
Pacific Islands Collectively called the Pacific Islands, the islands in the Pacific Ocean are further categorized into three major island groups: Melanesia, Micronesia, and Polynesia. Depending on the context, the term ''Pacific Islands'' may refer to one of se ...
such as the
Philippines The Philippines (; fil, Pilipinas, links=no), officially the Republic of the Philippines ( fil, Republika ng Pilipinas, links=no), * bik, Republika kan Filipinas * ceb, Republika sa Pilipinas * cbk, República de Filipinas * hil, Republ ...
and the
Loyalty Islands The Loyalty Islands Province ( French ''Province des îles Loyauté'') is one of three administrative subdivisions of New Caledonia encompassing the Loyalty Island (french: Îles Loyauté) archipelago in the Pacific, which are located northeast of ...
of
New Caledonia ) , anthem = "" , image_map = New Caledonia on the globe (small islands magnified) (Polynesia centered).svg , map_alt = Location of New Caledonia , map_caption = Location of New Caledonia , mapsize = 290px , subdivision_type = Sovereign st ...
. The geographic range is sporadic, for example, with populations distributed near the eastern and western coasts of Australia in the
Great Barrier Reef The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over over an area of approximately . The reef is located in the Coral Sea, off the coast of Queensland, ...
and the
Timor Sea The Timor Sea ( id, Laut Timor, pt, Mar de Timor, tet, Tasi Mane or ) is a relatively shallow sea bounded to the north by the island of Timor, to the east by the Arafura Sea, and to the south by Australia. The sea contains a number of reefs, ...
reefs, respectively. They do not, however, occur in the
Gulf of Carpentaria The Gulf of Carpentaria (, ) is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the eastern Arafura Sea (the body of water that lies between Australia and New Guinea). The northern boundary is ...
along the north coast.''Emydocephalus annulatus''
(2010). ''The IUCN Red List of Threatened Species''. International Union for Conservation of Nature.


Description

Named for its short, blunt head, this medium-sized snake has a slender build and varies in color. A single snake may exhibit only one color or may have banded patterns of white or yellow with dark rings. The scales on top of the head are large, regular, and entire. The
rostral scale The rostral scale, or rostral, in snakes and other scaled reptiles is the median plate on the tip of the snout that borders the mouth opening. Wright AH, Wright AA (1957). ''Handbook of Snakes of the United States and Canada''. Ithaca and London: ...
on the tip of the snout is conical in shape, and the second of three
supralabial scales In reptiles, the supralabial scales, also called upper-labials, are those scales that border the mouth opening along the upper jaw. They do not include the median scaleWright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates ( ...
is the largest. The body has 15–17 rows of smooth, overlapping scales. It has 125–145
ventral scales In snakes, the ventral scales or gastrosteges are the enlarged and transversely elongated scales that extend down the underside of the body from the neck to the anal scale. When counting them, the first is the anteriormost ventral scale that conta ...
, a single
anal scale Anal may refer to: Related to the anus *Related to the anus of animals: ** Anal fin, in fish anatomy ** Anal vein, in insect anatomy ** Anal scale, in reptile anatomy *Related to the human anus: ** Anal sex, a type of sexual activity involv ...
, and 20–33 single
subcaudal scales In snakes, the subcaudal scales are the enlarged plates on the underside of the tail.Wright AH, Wright AA. 1957. Handbook of Snakes. Comstock Publishing Associates (7th printing, 1985). 1105 pp. . These scales may be either single or divided (pair ...
. It may grow to in length. An individual snake's color affects the amount of algal
fouling Fouling is the accumulation of unwanted material on solid surfaces. The fouling materials can consist of either living organisms (biofouling) or a non-living substance (inorganic or organic). Fouling is usually distinguished from other surf ...
that accumulates on its body. A snake of a darker, more monotonous color has a higher level of algae build-up than one of a paler, patterned variety. The added weight of algae affects an individual's speed, reducing it by up to 20%. Those whose locomotive skills were affected had a tendency to be more inactive and choose to hide among the coral, while those with little to no algal fouling were found actively foraging. The inactivity, however, did not affect their survival rates; lighter-colored snakes were not more likely to survive than their darker-colored counterparts.


Dietary habits

The turtle-headed sea snake feeds solely on immobile demersal fish eggs, such as those of
damselfish Damselfish are those within the subfamilies Abudefdufinae, Chrominae, Lepidozyginae, Pomacentrinae, and Stegastenae within the family Pomacentridae. Most species within this group are relatively small, with the largest species being about 30 ...
,
blennies Blenny (from the Greek and , mucus, slime) is a common name for many types of fish, including several families of percomorph marine, brackish, and some freshwater fish sharing similar morphology and behaviour. Six families are considered "true ...
, and
gobies Gobiidae or gobies is a family of bony fish in the order Gobiiformes, one of the largest fish families comprising more than 2,000 species in more than 200 genera. Most of gobiid fish are relatively small, typically less than in length, and the ...
. The larger the snake, the more likely it is to feed on damselfish eggs, which lie in exposed areas, rather than blennies' and gobies', whose eggs are located in narrow crevices. ''E. annulatus'' populations tend to stay where they are and rarely move between territories. This could possibly be related to the spatial memory of snakes and their ability to remember where nests are located. If they stay in the same area, then the snakes are able to feed regularly on the same sites. Curiously, ''Emydocephalus'' is the only sea snake that does not possess palatal teeth. Contrary to the foraging habits of other snakes, the turtle-head tends to eat smaller, more frequent meals rather than larger, infrequent prey. In this respect, ''Emydocephalus'' feeds more like a grazing mammal than a snake. This atypical method of feeding is evidence of the great adaptive radiation of snakes.


Mating habits

Terrestrial snakes use pheromones to locate potential sexual partners, with a male often tracking a female's scent over large distances. This is not possible, though, in the aquatic environment of the turtle-headed sea snake. ''E. annulatus'' instead uses visual cues to search for mates. These include the size, movement, and color pattern of the object holding its attention. Upon locating females, the reception of female skin lipid pheromones by tongue-flicking males is necessary for males to continue courtship and mating. Turtle-headed sea snakes are
sexually dimorphic Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...
: the females of this species grow larger than males, and the rugosity of the scales is also greatly increased in males compared to females.


Conservation

In recent years, a steady decline in populations in and around the New Caledonian Lagoon has been reported. In 2003, volunteers spotted an average of more than six snakes per day within the protected coral reef snorkeling area in the lagoon, which decreased to less than two per day in 2011. In 2006, similar studies were also done in Ashmore Reef in northern Australia that exhibited a decline in population, as well. The cause of the decline is indistinct in either case, though the authors of both studies attributed it to human interference, habitat degradation due to tourism, coral bleaching, and habitat and diet complexity.


References


Further reading

* Krefft G. 1869. ''The Snakes of Australia; An Illustrative and Descriptive Catalogue of All the Known Species''. Sydney: Thomas Richards, Government Printer. xv + 100 pp. + Plates I-XII. (''Emydocephalus annulatus'', new species, p. 92). {{Taxonbar, from=Q2715108 Reptiles described in 1869 Taxa named by Gerard Krefft Snakes of Australia annulatus