Hydrus is a Southern Hemisphere constellation otherwise known as the Water Serpent (male). It is one of twelve constellations created around 1597 by Petrus Plancius (Wikipedia) from observations by the Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman. Hydrus remains one of the 88 modern constellations defined by the International Astronomical Union (Wikipedia).
Hydrus (abbrev. = Hyi; genitive = Hydri) covers 243 square degrees or 0.59% of the celestial sphere making it the 61st largest constellation. It contains 33 stars brighter than apparent magnitude 6.5, the brightest star being Beta Hydri.