Animalia --> Platyhelminthes --> Cestoda
Animalia --> Platyhelminthes --> Cestoda
Three Hosts: fish (threespine stickleback, Gasterosteus aculeatus), birds, and copepods
S. solidus is a simultaneous hermaphroditic parasitic flatworm that reproduces in birds and whose eggs are distributed in feces. Copepods act as primary intermediate hosts, followed by the three-spined stickleback that is consumed by any bird species, completing the cycle. Morphology changes throughout the life cycle: it is ciliated after emerging from an egg, becomes elongated and opaque in its first intermediate host, then produces proglottids before the definitive host eats it and it becomes the adult flatworm.
S. solidus relies on a three-host cycle. In it, aquatic species and especially copepods are susceptible to changing conditions where cold or excess heat might render reservoirs for the tapeworm uninhabitable. If copepods are not available to eat S. solidus eggs, the entire life cycle is thrown off.
This parasite's distribution follows that of its second intermediate host, the threespine stickleback, in western and eastern North America, Europe, and Eurasia.
Milinski, M. Fitness consequences of selfing and outcrossing in the cestode Schistocephalus solidus. Integr Comp Biol. 2006 Aug;46(4):373-80. doi: 10.1093/icb/icj044. Epub 2006 May 5. PMID: 21672749.
https://animaldiversity.org/accounts/Schistocephalus_solidus/
https://www.researchgate.net/figure/Parasite-load-of-Schistocephalus-solidus-from-a-single-Gasterosteus_fig13_327775867