Two bopyrid species parasitizing shrimps of the genus Thor along the Mexican coasts of the Gulf of Mexico and Caribbean Sea are known: Bopyrinella thorii, attaching in the hosts’ branchial chambers, and Loki circumsaltanus, attaching to the hosts´ abdomens. Herein, Bopyrinella hadrocoxalis sp. nov. is described, becoming the second described species of the genus in this geographic region. It is found parasitizing Thor manningi in a coastal area in Quintana Roo, Mexico. Loki circumsaltanus is recorded for the first time parasitizing Thor floridanus in Mexican waters; the oostegites, maxilliped and barbula are described and illustrated for the first time.