"Once the parasitic crustaceans enter the gills of a tadpole victim, they feed off the tadpole's tissues until male and female parasites mate. The male dies soon after. Meanwhile the fertilized female bores her way partially out of the tadpole.

The female worm's head and part of its body then morph into an anchor-like growth attached to the base of the tadpole's tail or to its legs. The parasite's egg sac is attached to this external growth, but part of the female parasite remains inside the tadpole's body and damages internal tissues. "

There is more information at the source article.