Some large projects have been in existence for very long times, and it does not feel entirely right to discuss them here. But there is one project, Nereus, that is relatively new. Its creator, Evan Black, does not mind, so that helps. Apparently Nereus received its name because humans first thought it was a water world (Nereus is a being from Greek mythology). The earliest post on the Nereus project on the Speculative Biology forum dates from May 2009. Evan has already produced 100 species and aims to achieve no less than 200 species. That is a lot or work: creatures have to be designed and described, and also drawn. I like the way Evan draws animals: while a bit stylised, they are very energetic, and as design they work: what you see are lively animals.
Here is a start: a rather large cladogram of current Nereid species. Don't be surprised to find that the one on Evan's site differs from the one here, because he might have added a new species by the time you go there...
The Speculative Evolution pages contain discussions and comments on how Nereus develops, but I much prefer to see the result on Evan's own site. There, you can work your way through the menu, clicking on the Latin names of the various groups until you get to individual species, but you do not see what you are aiming for until you get to the species pages. Once there each species has two pages: one with text and a thumbnail, which leads to a much larger image with additional text. But there is another way to browse Nereus that I much prefer, and that is to choose 'world', and then 'cartography and climates'. That will take you to a list of 7 biomes, and clicking on them rewards you with an overview of that biome and small images of the species in it, that you can then pick and read at will.
As an example, here is the 'Sog Basin'. Sog "carpets the landscape like a thick tangle of spongy red veins", which sounds a bit like Well's Martian weeds. Luckily, there are no intelligent aliens around to regard Earth with envious eyes (or not yet). Sog sucks up water from the few available sources, and transports it across the otherwise dry biome. Leaks in the sog create watering holes, on which many species depend. Now that is why I prefer creations with a background: you immediately start to think how that works, how such species might look, etc.
Here is one such species: the kappa (Nothorana pratensis). It is a predator lying in wait in sog ponds, with just its dorsal eyes and its nostrils above the water. Take a good look: the kappa has three legs: two paired front ones and one unpaired jumping leg in the back. The illustration also contains a classification list containing the familiar Linnaean scheme, which starts at the species level and goes all the way up to the phylum Tetrabrachia (that would be 'four arms', if I remember my Greek correctly). One of the nicest things about Nereus creations is that it all fits together. Look up the Tetrabrachia, and you will find a page devoted to their anatomical Bauplan.
And here it is. The four arms in question concern four major nerve trunks emerging from the central brain. One trunks goes upwards, and that one deals mostly with sensory functions, which in modern Tetrabrachia has caused them to develop a head. The other three trunks control movement. In effect, what we are seeing here are radially organised animals, and I like the idea of taking radial animals rather further than they have managed to do on Earth (see the discussion on tetropters here, here, here and you can more on tetropters yourselves; here is something about radial symmetry; if that is not enough, just search for spidrids on this blog). But the kappa does not show radial symmetry; it is blatantly bilaterally symmetrical, and the legend includes information just when that happened.
I cannot resist showing one particular specimen, and that is because Evan and I discussed its s flight mode. Again, this is a radial life form. Most flying forms on Nereus are bilaterally symmetrical, resulting in flight plans that are superficially similar to the ones on earth. Not so the Cliff Whistler (Cadosmilos Aetopsis).
As you can see, it flies a bit like my tetropters. The tetropter discussions may have helped inspire the Cliff Whistler, which is flattering. Anyway, the Whistler flies by beating its three wings horizontally to and fro. Diehards out there may remember that I made extensive use of the 'clap-and-fling' principle to explain tetropter flight. The 'clap' involves two wings beating against one another at the end of their movement, then sweeping back to the other end of their range, where they then clap against another wing. Etcetera. That works with two wings (Terran insects and some birds), four wings (Furahan tetropters) and would work with more wings too, although no-one has yet invented any of those yet as far as I know. Besides offering increased lift through 'clap-and-fling', an even number of radial wings neatly solves the problem of torque: if a wing moves clockwise it pushes the body counter clockwise, which is useless. With two or four wings these forces even out.
Three-winged radial flyers run into problems. There is no clap-and-fling mechanism, and the wings move in unison: all three clockwise, and then all three counter clockwise. That leaves torque to be solved. Well, evolution, in the form of Evan, designed an adaptation of the Whistler's mouth parts at its bottom: these evolved into winglets beating in the opposite directions of the main wings, countering to a degree. Enough for the Cliff whistler to be a viable organism, or so Evan and I thought.
Recently I came up with a way to have a clap-and-fling mechanism with just three wings though. It would increase lift but introduce some new problems. Again, Evan and I thought that it might work, but not necessarily better than the Cliff Whistler approach. Perhaps one species will emerge on Nereus with this particular mechanism, we would have to ask Evan. I am not going to tell you how it works, merely that it can be done: each of the wings A, B and C claps against another wing on the extreme ends of its movement range. I wonder if anyone will take the bait...