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.

I tried to draw something like that I tried to draw something like that

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.

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    $\begingroup$ Read "Grandpa" by James H. Schmitz. Grandpa is an animal that is also a self-propelled raft on an alien planet. A kid is taking out some adults (including a big-wig) for a trip when a bad interaction occurs for the first time. Lots of fun. $\endgroup$
    – NomadMaker
    Commented Nov 24, 2020 at 10:30
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    $\begingroup$ Here is a question about plant based living islands. worldbuilding.stackexchange.com/questions/116184/… $\endgroup$
    – John
    Commented Nov 24, 2020 at 15:26
  • $\begingroup$ @John. Now my objetive are animals but it could be useful. $\endgroup$
    – Drakio-X
    Commented Nov 24, 2020 at 15:28
  • $\begingroup$ I just left a comment on your question about the Quetzalcoatl. This one is similar, but is a poor candidate for the Anatomically Correct Series. Again, are you really interested in how such a creature would evolve? Or are you more interested in whether or not it can be represented in a story realistically? Please read the requirements for the reality-check tag and consider replacing evolution with it. $\endgroup$
    – JBH
    Commented Nov 24, 2020 at 17:22
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    $\begingroup$ In this case what I recommend doing is carefully explaining your living raft, and then tagging the question reality-check to let people comment on the strengths and weaknesses of your design. This one's different from your other question because such a creature, living half-in-half-out of water constantly, would be almost meaningless to explain in terms of real life. In this case, I suggest simply designing the creature and letting us help you ensure the design consistently reflects the rules of your world. $\endgroup$
    – JBH
    Commented Nov 24, 2020 at 20:00

2 Answers 2


Raft for food

The question is why it would be advantageous for the creature(s) to become a raft. If it's a raft without advantage, it'll only consume energy for being a raft, or even get used as a food source.

The easy answer is that being a part of a raft can provide nutrition to the creature(s). The life that'll thrive above can provide food by attracting birds and fish that want to get some food, as well as the life on top. The debris used for a raft can also provide some shelter against the elements and predation, allowing it to survive even better.

The creature itself could be a raft, but this isn't advantageous. It'll support less life and might've to offer some of it's own body as nutrition to the life on top. That is why the creature can gather debris in the ocean for extra surface space, protection and nutrients.

Groups of these creatures could band together for tiny floating islands where creatures will live. Much like the corals it'll attract all sorts of creatures, making it a small thriving eco system.

I would propose a form of man-o-war that gather the debris and form these islands. The thiving wildlife will provide them plentiful. If the need for self propelled creatures is required, it isn't a stretch that with abundant nutrients they form a propelling force to stay in advantageous waters. Possibly a sort of surface squid with tentacles long enough to grab food.

Only creature biome

The only creature biome would be near impossible. The fauna and flora on top would quickly turn parasitic. Unless it could turn the above into an advantageous strategy, I think it unlikely. Maybe a whale with a hard shell on top and stinging tentacles below? Again, creating a small biome might attract enough food, but the requirement not to dive will make food foraging with tentacles nearly mandatory for enough food "range".


Lets work this out what has to be true.

You creature cannot be a active-predator, it would spend too much time diving. It either has to be a filter feeding or use passive engagement like a man o war. An active predator large enough would have to be hunting constantly.

It should be ectothermic, endothermy requires too much energy to support a large passive animal.

It needs to not be bother by plants and animals on its back, so you don't want skin preferably a hard shell like a turtle or ammonite. Now huge ammonites 3-4 meters across have existed so you have a starting place, making them drift feeders is not impossible.

Brandon Sanderson had his Santhids enter image description here

a few fantasy artists have made convincing ammonite islands. enter image description here

More than one animal

You could alternatively have a community animals like a man-o-war or even like coral. You just need a coral that flats when dead and it will grow like and island. eventually storms will break it up so it will never get too large. the problem with a man-o-war is above a certain sizer the stuff in the middle is not getting any food so they would not be able to get very large but you could combine them with floating plants for a hybrid complex.

Let me leave you with one more idea I have used in an RPG, island making ants, ant that build islands out of debris. First ants do some crazy stuff so ants building small islands is not too far fetched. and mangroves swamps give oppurtunities for a middle ground for this to evolve in. They build nests in a way similar to arboreal ants by gluing material together. they would be able to actively maintain such islands. Now to work your ants need to be able to swim otherwise they starve but they can mostly live on farmed crops like plants or fungus. Attracting other living thigs wild help give them protection and supply fertilizer for the fungus, mutualism with sea birds might work. feathers for building and poop for fertilizer. Works really well in gyres where there is a lot of material available. Now these islands will very be that large, ship sized at the largest.

Of course you can always combine these ideas, floating coral farmed by crabs or ants would be believable.

  • $\begingroup$ Oh, an ant-like crab or the mentioned ants could be a very ineteresting concept, ants are very propense to symbiosis. Also before I considered the problems about the man-o-war and the corals, I really like these animals but I thought is needed a touch of a fantasy material for create a solid floating structure. And about the skin, Im not sure if it is really a problem, my spinosaurus I took some inspiration of this reddit.com/r/SpeculativeEvolution/comments/jr4925/… $\endgroup$
    – Drakio-X
    Commented Nov 24, 2020 at 16:38
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    $\begingroup$ @Drakio-X interesting, tricky though crabs don't have the halodiploid set up that makes eusocial behavior so east in ants. still possible though eusocial mammals exist. there is a newly discovered crab that builds a coral shell so maybe eusocial floating coral farming crabs. $\endgroup$
    – John
    Commented Nov 24, 2020 at 16:41
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    $\begingroup$ @Drakio-X the problem with a Spinosaurus is feeding it, if it dives things on top die. If lots of things are hanging on it it also swims much slower meaning it has an incentive to scrape off/kill anything growing on it. barnacles and coral on sea turtles are parasites not because they feed on the turtle but becasue they force the turtle to expend a lot more energy to hunt becasue they drastically increase drag. $\endgroup$
    – John
    Commented Nov 24, 2020 at 16:47
  • $\begingroup$ Maybe is hard to think about eusocial crabs (I think about a strange concept of involuntary eusocialism), but a giant crab could work good reddit.com/r/SpeculativeEvolution/comments/jvqnxf/… $\endgroup$
    – Drakio-X
    Commented Nov 24, 2020 at 16:49
  • $\begingroup$ Ive already thought about the problems that could bring a creature like this, my solution was that the spino-raft dont needs a high swimming, maybe some lazy, but if you see, there is a crab removing barnacles, birds are not problem, can fly and just use this for stand little periods, the problems are lizards and little mammals, so I thought about two principal symbiosis for this spino, an animal that helps for protect its eggs and animal that helps for hunting. $\endgroup$
    – Drakio-X
    Commented Nov 24, 2020 at 16:58

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