The Gammarus baysali, is a new species of cave-dwelling gammarid found in Turkey. Gammarus baysali belongs to the broader Gammarus pulex group and was scientifically described in 2013 from Cumayanı Cave Zonguldak Province. The most discriminant characters of this species are the minute eyes, densely setose fifth peduncle and flagellar segments of antenna 2, elongated pereiopods, and setose anterior margins of pereiopods 5 to 7. Additionally, the palp of right maxilla 1 has 4 setae along its outer margin.