" Xiphophorus andersi n. sp. from the Rio Atoyac, VeraCruz, Mexico is described: long head, moderately slender body, large dark black spot at the basis of the anal fin; adult male with short sword-like caudal appendage; tip of rays of gonopodium without a developed claw. Xiphophorus andersi n. sp. differs by the combination of distinct characters from all the other species of the genus known so far. The new species shows features of both the so-called platyfish species group and the so-called swordtail species group "