Flatworm

The Flatworm (ヒラムシ, Hiramushi) is a type of sea creature in the introduced in.

In
While initially absent from, the Flatworm was added in the 1.3.0 Free Summer Update.

In
Upon donating a Flatworm to the museum, it can be found in the large pool in the first room of the sea exhibit, along with many other species of sea creatures. It is found near the entrance of the exhibit. The exhibit has this to say about the Flatworm:

"Flatworms are flat creatures, and while some types look like Sea Slugs, they have little else in common. Some types are venomous and produce a poison similar to the kind blowfish are famous for. Flatworms are hermaphrodites and mate by fighting to determine the loser, who then bears the eggs."

In
When donating to the museum, Blathers will say the following:

''Marine flatworms are...well...flat and worm-like, as their name suggests. But while this sea creature is said to be quite simple, it does possess some rather remarkable powers. You see, when flatworms are injured, they can grow new body parts with ease. And when a flatworm is cut in half, each side can grow a whole new flatworm of its own. But most impressive of all...some flatworms can clone themselves without suffering a single cut! Ah, if only I, too, could safely divide myself in two. Hoo, imagine all the work I could do!"''

Real-world information
Flatworms are their own phylum, which includes tapeworms and flukes. Over half of all known flatworm species have parasitic behavior, which means that they thrive on another organism, a host, at the host's expense. Flatforms also lack a distinguished respiratory and circulatory organs, which is one reason for their flat shape. As a result, flatworms must rely on diffusion to take in oxygen while expelling carbon dioxide.