Specimens of
Spinitectus osorioi
Choudhury and Pérez-Ponce de León, an intestinal nematode species previously
considered to be specific to
Chirostoma
spp and endemic to some lakes in the Pacific drainage in Michoacán,
were collected from the freshwater fish
Atherinella alvarezi
(Díaz-Pardo) (Atherinopsidae) of the Michol River near
Palenque, Chiapas, Southern Mexico, which belongs to the Atlantic drainage system. Studies using light and scanning
electron microscopy revealed some taxonomically important, previously unreported or erroneously reported
features of
S. osorioi, such as the location of the vulva, the actual number and distribution of postanal papillae and
phasmids and the presence of a short median cuticular ridge anterior to the cloacal opening (in addition to two long
subventral ridges). The recorded somewhat shorter spicules (420-465 and 105-111 μm) and mostly smaller eggs (33-
36 × 18-20 μm) as compared to the original species description may be due to a different type of host, geographical
region or generally smaller body measurements of these specimens. These biometrical differences are considered to
be within the limits of the intraspecific variability of
S. osorioi. A key to species of Spinitectus parasitizing freshwater
fishes in Mexico is provided.
