Erabutoxins a and b are neurotoxins isolated from venom of a sea snake Laticauda 
semifasciata (erabu-umihebi). Amino acid sequences of the toxins indicated that 
the toxins are members of a superfamily consisting of short and long neurotoxins 
and cytotoxins found in sea snakes and terrestrial snakes. The short neurotoxins 
to which erabutoxins belong act by blocking the nicotinic acetylcholine receptor 
on the post synaptic membrane in a manner similar to that of curare. X-ray 
crystallography and NMR analyses showed that the toxins have a three-finger 
structure, in which three fingers made of three loops emerging from a dense core 
make a gently concave surface of the protein. The sequence comparison and the 
location of essential residues on the protein suggested the mechanism of binding 
of the toxin to the acetylcholine receptor. Classification of snakes by means of 
sequence comparison and that based on different morphological features were 
inconsistent, which led the authors to propose a hypothesis "Evolution without 
divergence."