The very first line of the Wikipedia entry on Gull says: "Gulls, or colloquially seagulls, are seabirds of the family Laridae in the suborder Lari. ". Colloquially speaking all gulls are seagulls.
https://en.wikipedia.org/wiki/Gull
The entry lists 54 species of Gull, and indeed from a pedantic perspective, none of their common names are "seagull". Nor are any of their binomial names Latin for "seagull". But there is Larus pacificus, either very calm or associated with the ocean of the same name. Also there is Larus atlanticus, and Larus Marinus (pretty dang close).