Exoanimals - 85MY

Exoanimals are the third and last multicellular clade to evolve on Reeccembra so far. They are heterotrophs and mostly get their food from the marine snow produced by the discuphytes at the ocean's surface.

While exoanimal anatomy greatly varies between species, all are based around a 'central tube' evolved from the' cell blanket' their ancestors were made out of curling up to connect its edges. This central tube is made out of hexagonal structures made from multiple cells, called compartments. Most of these compartments are made out of a single 'generator cell' (which makes more cells) surrounded by worker cells (which break down nutrients) and collector cells (which absorb nutrients), but in some species they have started to specialize into 'tissues' with different functions such as making new cells, collecting nutrients, and transporting said nutrients to the other compartments.

All exoanimals start out as two gametes, each containing a different part of a full cell, which fuse to create said cell. The 'begginner cell' then forms the first compartment, which begins making more compartments. Eventually the exoanimal embryo takes the shape of a solid cylinder made out of multiple compartments, it is only once this cylinder has reached the desired lenght that the true 'central tube' begins growing, half of it from each of the cylinder's sides, until the creature is fully formed.

When the organism has reached maturity, all of the outer compartments (in the case of unspecialized animals) or all the reproductive compartments (in the case of animals with tissues) start making gametes, which are expelled into the water around the creature. While males and females only make one type of gamete, hermaphrodites make both, maning that they have to first release one, then the other to avoid self-fertilization. The order of the gamete expulsion varies between species.

Tuboids:

Tuboids, as their name suggests, are simple exoanimals which only consist of the central tube and some cetae. Said cetae only grow inside the tube, near each end, and are also made up of unspecialized compartments.

Tuboids are filter feeders, using their cetae to capture falling marine snow and slowly digest it by expelling enzymes. As all of their body is made up of the same kind of compartments, all of their body can digest food, although only the cetae can keep it from sinking.

They can't swim, meaning that they have to be light enough not to sink, keeping their maximum size at around 10cm.

Pipes:

Pipes are another early exoanimal clade. They descend from a group of tuboids, and so have very similar anatomy. However, pipes do not float, they are attached to the ground with special 'roots' which grow from one end of their bodies. 

Since they are still a young clade, these 'roots' haven't had much time to specialize, and so are not very effective, strong enough currents can still uproot unlucky pipes and send them to the abyss below.

Another adaptation pipes have and tuboids don't are the basal pores. These small holes around the base of the organism (hence the name) are actually an early take on a throughgut, letting the nutrient-poor digested material which sinks to the organism's bottom float back out again.

Zooshrooms:

Another tuboid descendant, although a much changed one at that, is the zooshroom. Zooshrooms are the first multicellular detritivores to evolve on Reccembra, and, in only two million years they have managed to colonize most of the sea floor, from the coastal tidal pools to the coralliforme-full soil of the abyssal zone.

They are older than the pipes, and so have had more time to evolve their roots into actual structures not only used to stay attached to the soil, but also to absorb the nutrients in it. In this way, they are very similar to Earth plant roots, however the zooshrooms are not plants, and are only distantly related to the discuphytes of the surface.

Since they get all of their nutrients from the ground, zooshrooms have sealed both their ends shut, making them look even more plant-like and also making a water pocket inside their bodies which they can use to store nutrients.

Suckers:

The last sessile descendant of the tuboids are the suckers. Like pipes they only have one opening, however in suckers this opening is pointing downward, letting them 'suck up' the unicellular organisms and the detritis piling up on the sea floor.

Because no exoanimal has evolved any kind of muscles yet, suckers are stuck in one place after they become to heavy to float as zooplankton and fall to the ocean floor, meaning that for the rest of their life they slowly dig a hole beneath them, burying themselves as they slowly eat away at the soil.

Since expelling gametes from all of their body would be a massive energy cost considering most of the gametes released in the hole would die, suckers only release gametes from the top part of their 'skin', giving them more of a chance to float far away and find other gametes.

Bagbugs:

Moving on to floating exoanimals, bagbugs make up most of the zooplankton in the protocene. They are not direct descendants of any of the current tuboid species, however their ancestor was pretty similar to them. 

They are the smallest exoanimals, with the biggest specimens only reaching two centimeters in lenght. They feed by collecting ball grass and other small discuphytes in their body cavity and then digesting them by releasing enzymes.

Smaller bagbugs have bodies similar to those of pipes, only freefloating, but larger bagbugs had to make sure their food wouldn't float away through their one opening, so they evolved a larger 'stomach' and a smaller 'mouth', making sure any slight shaking of their body wouldn't spill the collected discuphytes back into the water.