Recurrent evolution

[acrosome]

As part of my scifi worldbuilding I'm trying to find examples of general life features that have evolved multiple times, and thus might presumably evolve independently on other worlds. Some I've found already include:

Multicellularity >40 times.
Eyes >40 times, and by far most are cameral eyes.
Bloodsucking through a proboscis at least 20 times.
Bioluminescence at least 19 times.
Exoskeletons at least 18 times, including things like mollusk shells.
Eusociality at least 10 times.
Hypodermic needles 10 times.
Toothless beaks 9 times, including fleshy ones like the platypus and hadrosaurs.
Electric organs 8 times (4 are strong enough to shock).
Plant carnivory 7 times (4 of these are "pitcher plants").
Winged flight 5 times.
IR Vision at least 5 times.
Opposable thumbs 5 times.
Crab-like body plan at least 5 times (i.e. flat decapods).
Limbs at least 4 times?
Color vision at least 4 times.
Hearing at least 4 times.
Ichthyoid body plan at least 4 times.
Echolocation at least 3 times, almost certainly 4.
"Limb loss" into a snake-like body plan 3 times.
Woody trunks at least 3 times.
Leaves at least 2 times.
Photosynthesis 1 time, though c4 photosynthesis then evolved 62 times!

Note that several of these- e.g. color vision- cannot really be preserved in the fossil record so all examples are extant and thus the number is almost certainly an underestimate.

Any obvious ones that I missed?

[PTTG]

Primary Endosymbiosis, in which one organism becomes effectively an organelle in another, is known to have happened three times. Once for mitochondria, once for chloroplasts, and once for nitroplasts, which is noteworthy because it's ongoing presently whereas the other two happened 1-2 billion years ago, nitroplasts began to merge in to Braarudosphaera Bigelowii only about 100 million years ago, and the process is still ongoing.

[Anthony]

Tentacles have evolved multiple times, though I don't have a count (wikipedia lists six examples) and since they're always soft tissue probably don't leave good records.

[Anaraxes]

Originally Posted by acrosome

Leaves at least 2 times.

There are a number of non-plants that have evolved parts, often broad and flat, to catch sunlight for various benefits including food. They may not be "leaves" in a technical sense, but that's a question of our jargon, not their function. Evolution doesn't care about the labels assigned by one species of primates, particularly on fictional alien planets, so it's up to you whether you want to count them as inspiration. Some of them are also cases of symbiosis and perhaps even points along the gradient of endosymbosis.

This article shows a few. (The full article requires a subscription; this link is to the short, but accessible, here's-some-pictures version.)

More familiar cases of leaf-like sun-catchers in animals might include some of the dinosaurs (e.g., Dimetrodon, Edaphosaurus, perhaps Stegosaurus), with those planar structures along the spine hypothetically used for temperature regulation. Butterflies use their wings to catch sunlight for similar purposes -- they have to reach a certain temperature to be able to fly, and they can do that via solar power rather than burning additional food for energy just to heat up. Many birds use their wings to catch sun as well. Sometimes these are evolved behaviors for other purposes, like getting rid of parasites, rather than food synthesis or temperature control. So, leaf-like structures to catch sunlight for reasons, but not for a specific chemical synthesis process like photosynthesis, are not uncommon, and thus possible features for your creatures, even if they're not counted as "leaves".

[thrash]

Chemical weapons? Venoms, sprays, etc.
Spines/thorns?

It might also be useful to consider biological features that are vanishingly rare, such as rotary motion (wheels) and projectiles.

[ericthered]

Legs and hands have evolved multiple times.
Mouthparts in general have evolved multiple times, though interestingly, they seem quite different.
both poison and venom seems to be constantly showing up everywhere
Live birth has evolved a surprisingly large number of times
As has direct fertilization of eggs (as opposed to spawning)
Parental Care shows up from Anteaters to Ants
Endoskeletons show up in echidnoderms as well as vertebrates

[pawsplay]

The form of winged flight found in mantises evolved separately from their next closest relative.

Hooves have happened a couple of times.

Re-adaptation to water has happened numerous times, from whales to certain frogs.

Mimicry, including flower, predator, threat, and eye mimicry, have happened an uncountable number of times.

[RyanW]

I'm only seeing four separate evolutions of winged flight: insects, pterosaurs, avian and near-avian therapods, and bats. If you included gliding, the number grows quite a bit higher, and you have to start asking more questions like "What is and isn't a wing?" (scansoriopterygid dinosaurs, flying fish, flying squirrels, maple tree seeds, etc.)

[Varyon]

Originally Posted by RyanW

I'm only seeing four separate evolutions of winged flight: insects, pterosaurs, avian and near-avian therapods, and bats. If you included gliding, the number grows quite a bit higher, and you have to start asking more questions like "What is and isn't a wing?" (scansoriopterygid dinosaurs, flying fish, flying squirrels, maple tree seeds, etc.)

If gliding counts, you may need to toss in orb weaver "parachuting" spiders.

On that topic, silk production has apparently evolved independently in a variety of arthropods. This article notes it evolving at least three separate times in arachnids and at least twice in insects, and there's some indication that it may have evolved independently in several subgroups. So that's probably a good one to add to the list.

[Fred Brackin]

Originally Posted by Anthony

Tentacles have evolved multiple times, though I don't have a count (wikipedia lists six examples) and since they're always soft tissue probably don't leave good records.

That defintion of "tentacles" appears to ignore functionally similar things such as prehentsile tongues, tails and elephant trunks.