The term "sea purse" can refer to a variety of objects commonly found in or related to the ocean. If you're looking for synonyms that convey a similar meaning, you might consider using words like "seaweed pouch," "oceanic moneybag," or "waterborne wallet." Other options might include "marine purse," "salty satchel," or "briny billfold." Depending on the context and tone of your writing, you may want to select a synonym that is more serious or more playful in its tone. With a little creativity, you can find the perfect word to give your writing an original and engaging edge.