Didymozoid Monilicaecum type trematodes in chaetognaths from the Mexican Caribbean Sea

Analyses of 22,508 holoplanktonic chaetognaths collected at 21 stations were made from four oceanographic campaigns along the coasts of Quintana Roo, Mexico, in 1991 (Caribe I = February; Caribe II = March; Caribe III = May; Caribe IV= August). Unencysted larval didymozoid parasites were identifi ed as belonging to the Monilicaecum type because of the arrangement of the chambers of the heavily twisted intestinal caeca, which occupy nearly the entire body. These larvae were found in the coelom of seven individuals of the chaetognath Flaccisagitta enfl ata (prevalence = 0.03, mean intensity = 1) and in two of Serratosagitta serratodentata (prevalence = 0.009, mean intensity = 1). The Mexican Caribbean Sea is reported as a new locality for this type of helminth larvae.