Answer: Echinococcus spp. protoscoleces
Shown here are multiple protoscoleces (larval tapeworms) of Echinococcus spp. The most common species to infect humans is Echinococcus granulosus, but E. multilocularis and less commonly, other species, may also cause human infection. Note that one larva has an everted protoscolex (below).
Based on the appearance of the everted protoscolex (above), you can see how this larval form will mature into the adult Echinococcus worm in the definitive canid host:
Adult Echinococcus granulosus worm
Higher magnification reveals the hooklets of the scolex, used to attach to the intestinal tract of the definitive host.
In echinococcosis, humans and herbivores are the intermediate host and are infected with the larval forms, whereas members of the Canidae such as wolves and domestic dogs are the definitive hosts and are infected with adult tapeworms.