Raft biome consists of a trunk or a group of plants that float in the sea and cant transports little animals like reptiles, birds, bugs or rodents, with this method many species can travel large distances and populate new lands, but the question is if its possible the existance of an animal that can fulfill this roll, rememring legends of living island (or islot), is not necesary biblical size, maybe just 10 meters (till 20m), but I dont know if its possible, because an animal needs move around feeds itself, and it implies violent moves, and swim on surface needs more energy and why other animals would be willing to live there, or how could live there.
So I thought in animals that can fulfill this function getting a symbiosis or comensalism advantage, but Im not convinced, a jelly fish like the man-o-war , like the ocean phantom, but can transport plants and cant travel far from coral reefs, a great filter, whales or speculative the balaenateuthia (https://speculativeevolution.fandom.com/wiki/Spec:_Balaenateuthia). And maybe turtles can develop a dome or pot shell.
Something like a squid or cuttlefish, because I remember that saw an speculative squid with boat form. Just Im sure that this animal needs a slower metabolism, a migratory pattern that make necesary get closer to islands, coast cliffs, mangorves swamps or great rivers or lakes connected to the ocean, and the most important a reason to swim near the surface all or almost the time.
Also I thought in the spinosaurus, but obviously the neural spine its not like a boat sail, but a double or triple spine could support little animals inside but again Im not sure if its possible and I dont know how could develop a symbiosis, but its the only one that I thought could get the size, breeding and migratory patterns for this.
Also there are many problems with an animal that needs to spend much time near to the surface with a big body surface out water for support other organisms, like what types of moves that need to do, displacement that could be viable because stay as boat and break the waves needs high amounts of energy what is in conflict with the eating behavior that this animal may have to dive and get all the necesary aliment.
How I mentioned, this biome is made with logs, vines or other stacked plants, initially I didnt considered fungi or plants for fulfill this "niche", because an animal that control its movements its more interesting for me than just float impulsed by the waves, but a giant lily pad-like gridle also could be interesting.