34
Heatwole 1999 ; Ineich and Laboute 2002 ; Aubret and Shine 2008 ). For example,
these adaptations were listed as follow: “Valved nostrils are located high on the
snout for breathing while swimming or basking at the surface. The belly is tapered
like the keel of a boat for stability in the water, and this snake lacks the fl attened
belly scales that give land snakes traction on the ground. The sea snake’s scales are
knob-like and fi t against one another like bricks, rather than overlapping as in land
snakes. The tail is fl attened and broadened to form an effective paddle for swimming,” ( “Yellow-Bellied Sea Snake” http://www.waikikiaquarium.org/experience/
animal-guide/reptiles/yellow-bellied-sea-snake/ , last accepted 25.05.2014).
Sea snakes possess corresponding physiological adaptations because they may
spend up to 90 % of their time underwater. These animals have no gill; however it
is known that their skin can act in the same manner. Space between the scales is
richly supplied with blood vessels, and, correspondingly, oxygen enters and waste
carbon dioxide leaves across the skin surface (Heatwole 1999 ). Here, one example
reported by Vogel ( 2003 ): “The sea snake Pelamis platurus , typically descends
about 30 m with enough air in its lung to be neutrally buoyant at that depth. But it
loses gas, mainly carbon dioxide and nitrogen, from its skin, whose permeability
lets it act as a kind of gill and supplement its lungs. So as it swims along it gradually
ascends, thus maintaining its neutral buoyancy as part of its requisite return to the
surface” (Vogel 2003 ).
Similar to marine iguanas (see above), sea snakes are able to excess salt from the
seawater and fi sh diet, however using special glands in the snake’s mouth (Taub and
Dunson 1967 ; Voris and Voris 1983 ). The presence of a salt gland in these reptiles
can explain their ability to survive in a hyperosmotic medium (Dunson et al. 1971 )
in contrast to their fresh water and terrestrial relatives which lacking this gland and
quickly die when placed in sea water. It was suggested (Dunson and Robinson 1976 )
about correlation between skin permeability, dermal respiration and differences in
salt gland size among sea snakes. The frequent skin shedding of sea snakes is
well known phenomenon and may be related to maintenance of low water permeability as well as to prevention the biofouling in marine environment (Dunson and
Freda 1985 ).
Fish eggs or crustaceans, mollusks or bottom dwelling fi sh like eels, are the main
components of the sea snake diet (Goldek and Voris 1982 ; Rasmussen et al. 2011a , b ).
However, sea snake bite is the cause of human fatalities as well. These animals are
known to produce venom that contains neurotoxins (Carey and Wright 1960 ), some
of them (erabutoxins) are similar to curare. These toxins can block the nicotinic
acetylcholine receptors on the post synaptic membranes (Tamiya and Yagi 2011 ).
Westhoff and co-workers ( 2005 ) described them as “predators that hunt during
the day, at dawn or at night. Like land snakes, sea snakes have scale sensilla that
may be mechanoreceptive, i.e. that may be useful for the detection of water motions
produced by prey fi sh. In addition, inner ear hair cells of sea snakes may also be
involved in the detection of hydrodynamic stimuli” (Westhoff et al. 2005 ).
Sea snakes provide an excellent model for studying the evolutionary transition
between the terrestrial and marine environments; as sea snake species encompass
a wide continuum in terms of the degree of their dependence on the ancestral
1 Introduction
Heatwole 1999 ; Ineich and Laboute 2002 ; Aubret and Shine 2008 ). For example,
these adaptations were listed as follow: “Valved nostrils are located high on the
snout for breathing while swimming or basking at the surface. The belly is tapered
like the keel of a boat for stability in the water, and this snake lacks the fl attened
belly scales that give land snakes traction on the ground. The sea snake’s scales are
knob-like and fi t against one another like bricks, rather than overlapping as in land
snakes. The tail is fl attened and broadened to form an effective paddle for swimming,” ( “Yellow-Bellied Sea Snake” http://www.waikikiaquarium.org/experience/
animal-guide/reptiles/yellow-bellied-sea-snake/ , last accepted 25.05.2014).
Sea snakes possess corresponding physiological adaptations because they may
spend up to 90 % of their time underwater. These animals have no gill; however it
is known that their skin can act in the same manner. Space between the scales is
richly supplied with blood vessels, and, correspondingly, oxygen enters and waste
carbon dioxide leaves across the skin surface (Heatwole 1999 ). Here, one example
reported by Vogel ( 2003 ): “The sea snake Pelamis platurus , typically descends
about 30 m with enough air in its lung to be neutrally buoyant at that depth. But it
loses gas, mainly carbon dioxide and nitrogen, from its skin, whose permeability
lets it act as a kind of gill and supplement its lungs. So as it swims along it gradually
ascends, thus maintaining its neutral buoyancy as part of its requisite return to the
surface” (Vogel 2003 ).
Similar to marine iguanas (see above), sea snakes are able to excess salt from the
seawater and fi sh diet, however using special glands in the snake’s mouth (Taub and
Dunson 1967 ; Voris and Voris 1983 ). The presence of a salt gland in these reptiles
can explain their ability to survive in a hyperosmotic medium (Dunson et al. 1971 )
in contrast to their fresh water and terrestrial relatives which lacking this gland and
quickly die when placed in sea water. It was suggested (Dunson and Robinson 1976 )
about correlation between skin permeability, dermal respiration and differences in
salt gland size among sea snakes. The frequent skin shedding of sea snakes is
well known phenomenon and may be related to maintenance of low water permeability as well as to prevention the biofouling in marine environment (Dunson and
Freda 1985 ).
Fish eggs or crustaceans, mollusks or bottom dwelling fi sh like eels, are the main
components of the sea snake diet (Goldek and Voris 1982 ; Rasmussen et al. 2011a , b ).
However, sea snake bite is the cause of human fatalities as well. These animals are
known to produce venom that contains neurotoxins (Carey and Wright 1960 ), some
of them (erabutoxins) are similar to curare. These toxins can block the nicotinic
acetylcholine receptors on the post synaptic membranes (Tamiya and Yagi 2011 ).
Westhoff and co-workers ( 2005 ) described them as “predators that hunt during
the day, at dawn or at night. Like land snakes, sea snakes have scale sensilla that
may be mechanoreceptive, i.e. that may be useful for the detection of water motions
produced by prey fi sh. In addition, inner ear hair cells of sea snakes may also be
involved in the detection of hydrodynamic stimuli” (Westhoff et al. 2005 ).
Sea snakes provide an excellent model for studying the evolutionary transition
between the terrestrial and marine environments; as sea snake species encompass
a wide continuum in terms of the degree of their dependence on the ancestral
1 Introduction