I don't recall the menus or the buffet lines ever really labeling what the shellfish content of individual selections was. However, it was always clear which items were seafood and which weren't. If you have any question or doubt, it would be prudent to ask for the information. I'm certain that the ship's staff would be quite understanding and accomodating to your concern. When ashore, however, this information may be more difficult to obtain.
Indeed, the ship's infirmary will carry epinephrine to treat anaphylactic (allergic) response. Can it be retrieved in time? I'd have to hedge here...I think so, but the ship is large and full of many spaces. My best recommendation if you are concerned about this, is to get your doctor prescribe you Epi-pen, usually used for bee stings, but appropriate for any anaphylactic emergency. This may be prudent, especially if you plan on disembarking for shore excursions.
I hope this helps your understanding, Joann. Enjoy your cruise!
John Burns, R.Ph.