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Can an organism have traits that resemble both an animal and a plant? Such as bone, chlorophyll, muscles, and cell walls. Not necessarily a hybrid, but something that can be classified in between the two kingdoms. Are there any examples of this if so?

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Photosynthesis is known to occur in one animal at this point, a specific type of green sea slug:

It’s easy being green for a sea slug that has stolen enough genes to become the first animal shown to make chlorophyll like a plant.

Shaped like a leaf itself, the slug Elysia chlorotica already has a reputation for kidnapping the photosynthesizing organelles and some genes from algae. Now it turns out that the slug has acquired enough stolen goods to make an entire plant chemical-making pathway work inside an animal body, says Sidney K. Pierce of the University of South Florida in Tampa.

green sea slug looks like a leaf Green Sea Slug Is Part Animal, Part Plant

It's not very big (average 30mm), but I think it's the closest you'll get to something "half animal, half plant" (at least in the real world).

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    $\begingroup$ I had not read of this slug. Excellent! $\endgroup$ – Willk Jul 15 '17 at 1:10
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    $\begingroup$ I was going to answer that animal metabolisms are too high. Photosynthesis just doesn't provide enough energy. Thanks for proving me wrong! I love it when nature has more imagination than I do! $\endgroup$ – Cort Ammon Jul 15 '17 at 3:30
  • $\begingroup$ @CortAmmon is there a plant whose metabolism is high, and animal whose metabolism is low? $\endgroup$ – Ooker Jul 15 '17 at 5:16
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    $\begingroup$ @CortAmmon Looking at the wikipedia article, it is questionable whether they actually use the chloroplasts as energy source. Experiments show no differnce between specimen deprived of food left in the dark or in the light. It is possible that the main "use" of these chloroplasts is, simply, the green colour used as a camouflage... $\endgroup$ – Bakuriu Jul 15 '17 at 13:28
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    $\begingroup$ Well, at least there are 4 animals now that can perform photosynthesis: umich.uloop.com/news/view.php/77109/… I must add that this slug and the salamander are my favorites!!! $\endgroup$ – Vylix Jul 16 '17 at 14:08
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This is coming from my 7th grade Biology lesson: Euglena viridis

Egulena viridis

When I read the title and question, I immediately remember this cute creature that drew me into the world of biology (and Planaria, I still remember your amazing regenerative ability - a natural Deadpool).

Euglena is a flagellate, a microorganism that moves using flagella, a whip-like "hair". It only got one, long, flagella, that categorized it as "animal" - actively moving, to gather its food.

However, the fascinating part is it got chlorophyll too, which is unique to plant kingdom, and can actually use it to perform photosynthesis when provided with sufficient sunlight.

So, basically you got an "animal micro-plant" here, half-animal, half-plant.

Note that the two kingdom - plant and animal - is outdated by now, and we now use 6 kingdoms model (or even 8 kingdoms, if you like).

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Your sugested ideas about what constitutes an animal are narrow. Basically, just vertebrates. Animals with bones and especially backbones. There are invertebrate animals that resemble plants, for example, sea anemones. Coral polyps also qualify.

There is a whole range of sessile animals that sufficiently resemble plants. They are immobile organisms, usually in their adult form, and they lack chlorophyll. It is their immobility that makes them plant-like (superficially, at least), but their larval stages are highly mobile.

The unicellular organism Volvox, which does form colonies, contains chloroplasts. It is both a plant and an animal. It is microscopic.

There are also stick insects -- if camouflage fits your plant-animal category. In principle, it is possible to imagine there could exist alien lifeforms that camouflage themselves as plants and might even possess chloroplasts.

The main drawback to plant-animal cross-over organisms is that photosynthesis doesn't confer much of an advantage. It would only supply, at best, a few percent of the energy intake for an animal. In general, animals can easily get all the energy they need by eating plants (herbivores) or other animals (carnivores) or both (omnivores).

In principle, creatures with both animal and plant characteristics might exist. So they are possible, but most likely they are highly improbable. In a big enough universe even highly improbable organisms must exist somewhere.

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In the real world Coral and Jellyfish are almost kind of there, Triffids come to mind immediately as well but I'm thinking those are less helpful to you. Both Coral and Jellyfish are animals that harbour photosynthetic algal organisms in a symbiotic fashion; it's not that big a step from symbiotic relationship to being an organelle although we don't understand the mechanisms that are involved. So that's Chlorophyll in animals covered, there are also some plants that exhibit the very animal behaviour of walking, except that they do it very very slowly one example is the "walking palm" Socratea exorrhiza which puts out roots on one side preferentially and thus very slowly moves away from salty seawater and inland, like a super slow-motion version of John Wyndham's Triffids and only in one direction. I'd also suggest watching time lapse of plants competing for light as they grow if you think plants don't exhibit mobility. As for something actually being "in between" in classification, that is unlikely to happen whoever gets there first will classify it, if the discoverer is a botanist it'll be a plant and otherwise if it walks it's going to be an animal that's just human nature.

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Aside from the sea slug already mentioned, I don't know of any other animals that photosynthesize but other crossovers do exist.

There is an entire phylum of photosynthetic bacteria called cyanobacteria. These are bacteria that obtain their energy through photosynthesis which takes places in folds in the outer membrane of the cell, so they do not have chloroplasts. (Small edit: A friend of mine gave the remark that cyanobacteria are essentially what became chloroplasts, so it is kind of logical they do not have chloroplasts)

Lichens are composite organisms that consist of algae or cyanobacteria that are symbiotic with fungi. One cannot live without the other, and so the combination of the photosynthetic organism and the fungi is called one single organism.

Again, these are not combinations of plants and animals, but they do show that it is possible for other organisms to have plant-like abilities. As was already mentioned before so far photosynthesis outside of plants only happens in very small organisms, because larger organisms have a too high metabolism.

However what I could imagine is a 'larger' animal using photosynthesis as an additional way to gain energy. The first imagine that pops up for me is a cold blooded animal that does a lot of sun basking already. Why not gain some additional energy at the same time?

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  • $\begingroup$ fascinating stuff. $\endgroup$ – Fattie Jul 15 '17 at 13:06
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    $\begingroup$ I was going to propose something similar. Possibly some sort of desert reptile that is able to go into an aestivation like state where their metabolism drops enough for them to survive long periods without food using a mix of photosynthesis and built-up fatty tissue. Although my biology is a little rusty so I'm unsure if that would be possible, perhaps someone could clarify for me? $\endgroup$ – Braeden Orchard Jul 16 '17 at 5:04
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    $\begingroup$ That would be an interesting idea, and I think it would be possible. The only unlikely thing about this is that animals that go into a brumation like state usually hide away. If their metabolism drops they are unable to react quickly to any danger or other things that need to be reacted to. And the moment it is hidden away sunlight wont reach them. I also got the suggestion that it would be an interesting addition for animals living in the desert but would be able to reach water. Then they can gain energy from the sun, and drink some water, but don't need to rely so heavily on food sources. $\endgroup$ – Talkenia Jul 17 '17 at 8:10
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There are a couple of ways something like this could happen:

  • They could have branched off far back in the tree of life, when plants and animals were more similar, and retained primitive traits of both. Fungi, sponges and microorganisms that can either photosynthesize or hunt all fall into this category, although they don’t have the more advanced traits you’re thinking of.
  • Plants live in symbiosis with chloroplasts, which are genetically separate organelles. (They evolved from a cyanobacterium that survived getting eaten by another microbe, and started making food for them both.) We tend to think of green and photosynthetic as plant traits. Other kinds of organisms can do something similar, with a chloroplast from something they ate, or an organism containing them, or a different kind of algae.
  • Traits such as hard cell walls might evolve independently.
  • Individual genes might hop species due to horizontal gene transfer, although genes are not Lego sets. This gets you an animal with a protein from a plant or vice versa, not an animal with hard cell walls.
  • They could be alien or genetically-engineered.
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  • $\begingroup$ Your 2nd point is what scientists think how eukaryotic cell evolved: endosymbiosis. It's even more interesting that there is something called "composite organism", a symbiosis between two completely different organism; one of them is Lichen. Again, this is coming from my 7th grade Biology. Now excuse me, I must thank my former teacher for that. $\endgroup$ – Vylix Jul 16 '17 at 14:01
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The reproductive cycle of jellyfish has distinctly animalike and plantlike elements. They reproduce by dropping a "planula" into the water, which attaches to a rock and grows into a polyp (which looks like an anemone). The polyp then clones itself over time, producing more jellyfish.

The polyp more resembles a plant/spore more than an animal, at least to me.

In fact, the fact they stay so stationary, that many anemones seem a lot like plants, but they're most definitely animals. Coral, also, is in fact an animal, technically speaking, but behaves much more like how we imagine plants. (Corals, anemones and jellyfish are all related.)

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  • $\begingroup$ Welcome to Worldbuilding @FeathersMcGraw! I've edited your post to be more of an answer than a comment. We are particularly strict about keeping answers and comments separate here. Please check out our tour when you have the time. $\endgroup$ – sphennings Jul 17 '17 at 16:13
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All life has a common ancestor, and both plants and animals originated from early multicellular life which possibly had features of both. For example corals have a sessile (plant-like) adult forms, and motile (animal like) larval forms.

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One organism with both plant-like traits and animal-like traits is the Venus Flytrap.

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    $\begingroup$ Can you flesh out a bit more this? It looks more like a comment than an answer. $\endgroup$ – L.Dutch Jul 16 '17 at 8:59
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    $\begingroup$ This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post. - From Review $\endgroup$ – L.Dutch Jul 16 '17 at 8:59
  • $\begingroup$ I was about to post an answer on the Venus Flytrap but you beat me to it. As @L.Dutch mentioned, it would be helpful to add some more information. To get you started, the Venus Flytrap is a carnivorous plant of the US east coast. It does not have muscle tissue per se, but it has an analogous structure that allows it to fold its leaves lengthwise to trap insects. It also has a sense of touch and a digestive system. They aren't harmful to humans. $\endgroup$ – Robert Columbia Jul 16 '17 at 13:31

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