Pricecheck: A race of sentient corals, which thinks of itself in terms of colonies rather than individuals, with four life stages:
A freshly budded colony looks like a small wind-up toy car, which drives around until it encounters a sufficient food source (the coral eat decaying organic matter by filter-feeding, extending delicate feathery 'roots' which secrete mucus that traps food particles), whereupon the polyps begin dividing and the colony expands into the second stage.
After having fed sufficiently to fuel reproduction, the colony now looks outwardly like an ordinary human, complete with clothing and other accoutrements made out of secreted coral exoskeleton. Second-stage colonies are also mobile, but instead of seeking food, they seek mates in the form of other second-stage colonies. When two second-stage colonies join, they grow together and form the third stage.
Third-stage colonies quickly develop to take the appearance of a large tree. New first-stage colonies continually bud off from the branches and fall like fruit. The third-stage colony continues to feed, fuelling both its own growth and the budding process. Eventually, it grows large enough to reach the fourth stage.
In the final stage of its life, a colony takes the shape of a huge building outfitted as a dance hall. Having passed its reproductive prime, it now acts to aid the reproductive success of its second-stage offspring by providing them with a place to meet potential mates. As long as polyps remain alive, the colony can reconfigure itself to serve its goals; however, the colony has reached senescence and its polyps will slowly die off, eventually rendering the dance-reef wholly passive. If food is readily available, second-stage colonies meeting there are likely to choose to grow into the sessile third stage directly attached to the existing structure, growing the reef.