The viewers had a lot of good suggestions for this case, given the unusual location of a round worm in the periumbilical skin. Some suggested that this could be Dirofilaria, Onchocerca volvulus, or a worm causing cutaneous larva migrans - all possible causes of a subcutaneous nodule.
However, the key to making this diagnosis is not the history (although it can fit with this worm), but instead, the classic histologic features, including relatively large size and prominent lateral cords (the latter which are characteristics of the anisakids).
As most of you know, the anisakids, including Pseudoterranova decipiens and Anisakis spp., are acquired by eating undercooked or raw fish. Once ingested, the worms may pass through the gastrointestinal tract, get coughed up, or in the worse-case scenario, attempt to burrow into the intestinal tract. Burrowing worms cause severe acute pain, typically necessitating their endoscopic removal. Rarely, the worms can perforate the intestinal tract and enter the peritoneal cavity.
My guess in this case is that the worm penetrated the small or large intestine and ended up lodged in the peritoneal wall resulting in a palpable periumbilical nodule.