Thank you for your question. In this specific situation, I would say that you should speak with a doctor
. Depending on the part of the world in which you were swimming at the time, there are some animals and shells that can have very poisonous stings or bites that can cause serious problems. While it is not clear which animal this may have been, the best and safest course to pursue is to visit a doctor as soon as possible. If it can safely be accomplished, it can sometimes be helpful to collect the animal or creature that has caused the bite or injury
, but not if this risks another wound or prolongs the exposure. In this manner, the doctor will be able to identify what it was and help with the further steps that need to be taken. In most cases, the minimum intervention that is needed is to update the tetanus vaccination in the event of a wound that pierces the skin. At most, further intervention may be needed that requires more invasive therapy or monitoring. Please speak to your doctor as soon as possible to get the help that you need.