Life Cycle: “Diplostomum spp. are trematode parasites that spend their life cycle in three hosts. In fish-eating avian hosts, Diplostomum spp. produce eggs that under favorable conditions hatch into small, short-lived aquatic miracidia, which invade snail host(Chappell et al 1994). Cercarial larvae emerge from the lymnaea snails, which are the first intermediate hosts, and settle in the eyes of their fish hosts, causing cataract blindness (Shariff et al. 1980)” (Voutilainen et al., 2009).
Body usually bipartite; hindbody shorter or longer than forebody, rarely conical. Anterior extremity trilobate; pseudosuckers present. Oral sucker, ventral sucker and pharynx small; caeca reaching close to posterior extremity. Holdfast organ round or elliptical, with median slit. Testes tandem; anterior asymmetrical; posterior symmetrical, bilobed, ventrally concave, with lobes more or less longitudinally elongate. Ovary ellipsoidal or ovoid, pretesticular, lateral to and contiguous with anterior testis. Vitellarium in fore- and hindbody, extending forward beyond ventral sucker. Copulatory bursa in form of cavity of variable depth with opening of short hermaphroditic duct at its base. Small genital papilla very occasionally present. In intestine of various birds. Cosmopolitan. Metacercariae of 'diplostomum' type, in fishes. Cercariae with four large penetration glands posterior to ventral sucker; flame-cell formula 2[(1+1+1)+(1+1+1+2)]= 16.
Sources: Bray, R.A., Gibson D.I., and Jones, A. 2002. Keys to the Trematoda, Vol. 1, p. 174.
Voutilainen, A., Ooik, T.V., Puurtinen, M., Kortet, R., and Taskinen, J. 2009. Relationship between prevalence of trematode parasite Diplostomum sp. and population density of its snail host Lymnaea stagnalis in lakes and ponds in Finland. Aquatic Ecology. Vol. 43, p. 351-357.