A study on the spatial distribution of two congeneric monogenean species Pseudodactylogyrus anguillae Yin ct Sproston, 1948 and P. bini Kikuchi, 1929 on the gills of large size European eel Anguilla anguilla (L.) were conducted. Results were analysed with regard to: single-species infection, mixed infection and general occurrence of the parasites in the ccl population. Statistical analysis revealed that the distribution of these species on the gill apparatus is fairly similar and the zones in which they occur more numerously coincide to a great extent. However, a number of differences were found. Both the possibility of simultaneous occurrence on Ihe host and similar distribution of the above species on the eel’s gills indicate the reciprocal tolerance of these parasites.
Pseudarhahdttsynachus yucatanensis sp. n. (Diplectanidae) is described from the gills of the red grouper, Epinephelus maria (Valenciennes, 1824) (Serranidae), from the coast of the Yucatan Peninsula, Mexico. This new species is characterized by having both the ventral and the dorsal squamodiscs composed of 10-12 rows of rods, with 0-1 innermost row forming a closed circle. Furthermore, the vagina of P. yucatanensis has a non-sclerotized ampulla with a fine, sclerotized duct leading to a sclerot-ized seminal receptacle. Prevalence (percentage of infected fish) and abundance (mean number of worms per examined fish) were estimated for P. yucatanensis from 8 localities along the coast of Yucatan. Prevalence varies from 38% to 100%, while abundance was between 1.2 ± 0.6 and 43.2 ± 17.8 worms per ftsh. The lack of linear relationship between the host length and the number of monogcneans per fish (regression F, = 0.56. p = 0.45) was probably due to the fact that the sample was restricted to juvenile hosts.