Marakihau, while not being a species of dragon or serpent specifically, are carved representations of the formidable taniwha. Across New Zealand, meeting houses have Marakihau, which are generally depicted with fish-like bodies below the waist and heads similar to humans, save for the long, terrible, hollow tongues. The tongues are used to suck down fish, which taniwha do regularly, as well as people and waka (canoes). 
Taniwha, however, are described in stories as in the form of whales or sharks, and rarely do stories tell of taniwha having the hollow tongues present in Marakihau. This is why there is a separate term for each of them; but Marakihau often are part of retelling taniwha stories. 
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