Karkinos in Wikipedia
In Greek mythology, Karkinos or Carcinus (a transliteration of the Greek word for "crab") was a crab that came to the aid of the Lernaean Hydra as it battled Heracles, bottom left. Karkinos bit Heracles in the foot, but was crushed beneath the hero's heel. For its efforts, however, Hera placed the crab amongst the stars as the constellation Cancer. It is one of a large number of constellations that memorialise the labours of Heracles. The Karkinos is mentioned in the Bibliotheca of Pseudo-Apollodorus, the Euthydemus of Plato, and the Astronomica of Pseudo-Hyginus.