The full answer
Do not assume that every creature described commercially as “seafood” has exactly the same ruling as fish.
For the HMS website, questions about individual sea creatures should follow the rulings of the Shariah Board of America rather than being generalized from the word “seafood.”
Fish itself provides the clearest everyday category.
Answers in the Halal Knowledge Center reflect the standards followed by Halal Monitoring Services (HMS), which operates as part of the Shariah Board of America. HMS certifies only what it checks.