A new species of (Crustacea, Copepoda, Calanoida) and a first record for stygobiotic calanoid fauna from a cave in Thailand.

A new species of Calanoida belonging to the genus Fosshagen & Iliffe, 1989 was found in a freshwater pool within a cave of the Satun province, South Thailand. It is the first record of the genus and of a stygobiotic representative of calanoid fauna in this country. The new species is most similar to Fosshagen & Iliffe, 1989, based on position of genital pores, structures of P4 and P5 in both sexes, relative length of subapical spine vestige on the male right P5, and shape of the male left P5 endopods. However, this new species is distinguished from its known congeners by: (1) relatively longer distal outer spines on the male right P5 exopods, (2) smaller endopods of the male left P5 and (3) elongated apical spines on the distal exopodal segment of the female P4 and P5. Furthermore, the distinctive characteristic of the Thai is the presence of inner minute seta on the distal segment of the male right P5 exopod. Detailed descriptions of the new species and a key to all six known species of the genus is provided.