Mesostoma (Platyhelminthes: Rhabdocoela, Typhloplanidae) of Mona Island, Puerto Rico, with a description of a new species

Mona Island, a small uninhabited Caribbean island between Puerto Rico and Hispaniola, was surveyed for freshwater platyhelminths. Rainwater pools on the island's plateau produced two species of Typhloplanidae, a species close to Mesostoma georgianum and a new species of Mesostoma, M. tubiseminalis, herein described. The new species is diagnosed by the presence of a tubular receptaculum seminis that forms a distinct bifurcation of the female tract. Pools inhabited by both species are subject to high pH, high temperatures, and rapid evaporation. While M. cf. georgianum is quite conspicuous and creeps on the surface film, the new species lives concealed within the substrate and rock crevices of the pool.