Zitharta

How terrifying it would be if such an object were to loom above the White House, its gigantic hull casting a deep, dark shadow, its jet-engines droning with an ear-shattering noise and its tentacles quivering in anticipation of grabbing up some hapless humans. Thankfully though, the Zitharta is not an alien spaceship coming to invade Earth, but a small, harmless aquatic animal, only as tall as a thumb!

The zitharta is an enigmatic arezoan, for a long time wrongfully classified within the waste-basket taxon “Brachiostoma”, solely due to its tentacles. By the looks alone it is apparent that this animal’s anatomy is a world apart from most other arezoans. Its body consists of a main mantle, somewhat shaped like a professional bicycle helmet worn at the Tour de France. It is what holds all the internal organs and is supported by a siliceous endoskeleton, not unlike a glass sponge. At the front is a frilled mouth with two fan-like tendrils, which the zitharta uses to capture food particles and small prey out of the water. Above the mouth is a three-rowed series of small ocelli, each one coming with its own eyelid, which sometimes configurate into amusing expressions.

Most conspicuous about the zitharta is of course its “mast”, a long, rod-like appendage that grows underneath the mantle. The “mast” is supported by a sturdy biosilicon rod and hinged at its upper end. On it grow ten pairs of little tube-organs, which, through peristaltic pumping, can create a continuous and coordinated water-flow. This form of jet-propulsion, perhaps the most complex so far encountered in the solar system, is the main method of locomotion of this animal. The two fleshy fins at the bottom end of the “mast” seem to mainly function as steering rudders. An air-filled bladder inside the mantle allows for changes in buoyancy.

Zitharta live in very deep caverns and subglacial lakes of the southern hemisphere, whose waters stay liquid all year round, thanks to the planet’s remaining interior heat. In these very dark environments, they help themselves with a large skin-patch on the posterio-dorsal mantle which houses bioluminescent symbionts. With these biolights the zitharta can navigate their way through the dark waters while also attracting small planktonic organisms.

This is as far as our knowledge on these animals goes. On a drying Mars, these aquatic, subterranean creatures are exceedingly rare and difficult to observe. We do not know, for example, what they do during times of seasonal anoxia, though metabolic strategies similar to other cave-dwellers seem quite likely. We also do not know how they reproduce or what other animals prey on them. Finally, there remains the question of their aforementioned phylogenetic status. After the break-up of Brachiostoma, zitharta have become notorious problematica. They possess a U-shaped gut, with the cloaca emerging right below the feeding tentacles, which has prompted some researchers to place them close to the Antitremata, but the usage of biosilicon is virtually unknown in said phylum and there are other glaring differences. The discovery of the closely related githarta and zotharta beneath the northern polar caps has also not helped the matter, as they still closely resemble the zitharta. Nonetheless, the growing amount of taxa has made some researchers more comfortable with classifying these organisms within their own, distinct phylum Trabsozoa. Micropaleontologists have found the distinctive rods of trabsozoans in ancient chert deposits, indicating that these lifeforms could have already existed when Mars still had oceans.