Littorina saxatilis, L.obtusata and Onoba aculeus growth

The daughter sporocysts of Microphallus pseudopygmaeus were located in the Onoba aculeus gonads. Microphallus piriformes sporocysts were located in the gonad - digestive gland complex of both Littorina species. This type of localization leads to parasitic castration in both sexes. Microscopy of the gonads showed the absence of active spermatozoids in infected males in contrast to uninfected ones. Furthermore, infected males of both Littorina species exhibited significantly reduced penis size (t₂₂=3.56; P<0.05 — Littorina saxatilis and t₃₈=8.26; P<<0.0001 — L. obtusata). The number of eggs and embrions in the reproductive systems of infected females of all three snail species varied from none to very few and was always less than in gonads of uninfected individuals.
The growth patterns of L. saxatilis, L. obtusata and O. aculeus are shown in Figures 4 A,B and 5. The snails’ growth rate correlates negatively with the individual shell size at the beginning of the growth season. The smaller shell diameter at the moment of winter-grade line formation, the higher angle gain at the date of sampling.
Infestation with Microphallus piriformes had not induced any significant changes (t₆₅=0.76; P>0.05) in growth rate of L. saxatilis (Figure 4A). Growth rate of L. obtusata infected with the same species significantly (t₈₉=2.49; P<0.02) decreased in comparison with uninfected ones (Figure 4B). In contrast, O. aculeus infected with M. pseudopygmaeus displayed a significantly (t₁₈=6.5; P< 0.0001) increased growth rate (Figure 5).