Jᴀᴄᴜʀᴜᴛᴜ - Tʜᴇ Cᴀsᴛ Oᴜᴛ

I recently came across this obscure 100-year "mystery" and thought of the Sandtrout and how they require unique environmental conditions to become Sandworms.

According to the Facetotecta page on Wikipedia:

Facetotecta is a poorly known infraclass of thecostracan crustaceans. The adult forms have never been recognised, and the group is known only from its larvae