Synalpheus regalis is a unique species of sponge-dwelling snapping shrimp, and the first described example of eusociality in the sea (Duffy 1996a). Like social insects such as ants and honeybees, Synalpheus regalis lives in large colonies consisting of one breeding female "queen" and typically 100 or more non-breeding workers that jointly defend the sponge against intruders (Duffy 1996b, 2007). Allozyme work has confirmed that most colonies consist of full-sibs produced by the queen and possibly a single male "king."

S. regalis belong to the gambarelloides species group in the genus Synalpheus, and molecular work suggests that eusociality evolved independently at least three times in this group.