11 July 2006 PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON ll9(2):222-238. 2006. A new epacteriscid copepod (Calanoida: Epacteriscidae) from the Yucatan Peninsula, Mexico, with comments on the biogeography of the family Eduardo Suarez-Morales, Frank D. Ferrari, and Thomas M. Iliffe (ES-M) El Colegio de la Frontera Sur (ECOSUR), Chetumal A.P. 424. Chetumal, Quintana Roo 77000, Mexico, and Research Associate, National Museum of Natural History, Smithsonian Institution, e-mail: esuarez@ecosur-qroo.mx; (PDF) Department of Systematic Biology, National Museum of Natural History, Smithsonian Institution. Washington. DC. 20013-7012. U.S.A.. e-mail: ferrarifC«)si.edu; (TMI) Department of Marine Biology, Texas A&M University at Galveston. Galveston, Texas 7755.3-1675, U.S.A.. e-mail: iliffe@cavebiology.com Abstract.—The calanoid copepod family Epacteriscidae is represented by species from tropical marine and anchiahne environments. Surveys of the anchialine invertebrate fauna of the Yucatan Peninsula. Mexico, have resulted in a number of interesting records of crustaceans during the last decade, but no records of Epacteriscidae. However, recent collections from hypogean environments of the Yucatan have yielded specimens of a new species of the previously monotypic genus Balinella. The specimens were included in this genus by having three outer spines on the third exopodal segment of legs 3 and 4, a biramous mandibular palp, and an antennal endopod longer than the exopod, among other characters. The new species, B. yucatanensLs, is described on the basis of male and female specimens collected in caves associated with three different karstic sinkholes. The new species is distinguished from its only known congener. B. ornate/ Fosshagen, Boxshall and Iliffe, 2001. by the strong asymmetry of the caudal rami in females, a modified left fifth leg of the male in which the proximal and middle exopodal segments are attenuate at the point of origination of the outer spine, and by differences of the armature of mouthparts (mandibular palp, maxilla, maxilliped). This report extends the range of Balinella from anchialine caves of the Bahamas to hypogean waters of the Yucatan Peninsula. The introduction of epacteriscid copepods onto the Yucatan Peninsula may be an old event; diversification by genera into non-cave habitats appears to be secondary. The family Epacteriscidae is one of the Fosshagen et al. (2001), in which 9 new most representative copepod taxa in the genera were described and a phylogeny of anchialine and troglobitic environments, the known species of 12 genera was together with the Ridgewayiidae (Fossha- proposed. About the same time, Jaume gen et al. 2001). The current distribution & Humphreys (2001) described a new of the Epacteriscidae in geographically genus, Bunderia, from anchialine waters distant sites such as the Galapagos, Fiji, in northwestern Australia, and Boxshall and the Bahamas seems to be related to & Jaume (2003) described the genus a very old biogeographical pattern that Ihoyclla from an anchialine cave in Cuba, may be linked to the Cretaceous period. Quite recently, Fosshagen & Iliffe (2004) A revision of the family was published by described 3 additional monotypic genera