Two species of the chaetognath family Spadellidae were recorded in a reef-related environment of the Mexican Caribbean; one of these spadellids represents a new species which is described and compared with its congeners. Spadella xcalakensis, new species differs from the other species of the genus by having a unique suite of taxonomically relevant structures such as the structure of the female genital opening, the shape of the seminal vesicles, the arrangement of the lateral and caudal fins with respect to the seminal vesicles, and the eye pigmentation. The nominal S. cephaloptera Busch was also recorded in the area; inconsistencies in the morphological descriptions related to this species worldwide suggest that it probably represents a species complex. These records set the southernmost distribution range for this genus in the Atlantic Ocean and the first record in Mexican waters. A dichotomous key for the identification of the currently known species of Spadella is included herein.