perlo

The seam you can see is not there. Per is one of the commonest words in Esperanto, the preposition of means: per aŭto, per mano, per mono. So perlo offers itself as per plus something, and the something would have to be -lo. There is no -lo suffix in Esperanto, official or otherwise. Perl- is a single borrowed root and the preposition per is unrelated to it, coming instead from Latin per, through. Two identical letters, two separate imports, no join between them.

Elision makes this worth checking twice. Rule 16 lets a poet drop the final -o of a noun, so perlo can appear as perl' in verse, and the bare root perl is registered on this site's index as a form of this word. In prose, though, a stray perl is far likelier to be a typo than an elision. If you meet per la written as one word you have found somebody's missing space, not a pearl. See poetic Esperanto for how far the apostrophe reaches.

Derivations, and one good compound. Perla is pearly, perleto a seed pearl, perlulo a pearl fisher. The compound worth knowing is perlamoto, mother-of-pearl, which is a straight loan translation of French nacre displaced by German Perlmutter, mother-pearl, and it means the shell lining rather than the pearl itself. Figuratively perlo works exactly as English gem does: the best thing in a collection, la perlo de la kolekto. And there is a Latin curiosity waiting three ranks later at unio, which in Roman usage meant a single outsized pearl.