Hydra

The constellation Hydra resembles a twisting snake, and features as such in some Greek myths. In Greek mythology, a crow serves Apollo. It is sent to fetch water, but it rests lazily on the journey, and after finally obtaining the water in a cup, takes back a water snake as well, as an excuse. According to the myth, Apollo saw through the fraud, and angrily cast the crow, cup, and snake, into the sky. The origin of this story is likely to be the juxtaposition of this constellation with those of Crater, and Corvus, in the area of the sky known as the Sea.
The Hydra was also considered to be the Lernaean Hydra (as defeated by Heracles for one of his Twelve Labours) by the Greeks. Its position in the sky (below the ecliptic), together with the constellation Cancer (which lies near its head) may be the origin of parts of the myth.