Chiropede Shrubs

Most of the common chirorbites  live lives not unlike arezoans. They are born from simple eggs or through live birth after two parents mate and impregnate each other and go on to live by feeding on smaller animals or plant matter. But not all of their members have forgotten their roots in what is actually Mars’ flora.

One sub-group of the Chirorbita reproduces in a unique way. The chiropedes, which have elongated bodies and often only a single eye, begin their lives as plants. When two adult chiropedes mate, they lay an egg into the ground which hatches into a tiny, worm-like larva that buries its head into the soil and becomes a sessile organism, whose tissues house photosynthetic zooxanthellae. As the frond of this plant grows, it begins producing leaves at its tip, which eventually form into a fan-like canopy. As some of these leaves mature, they begin growing a hardened tunicine exoskeleton, feelers and eyes. Eventually, some of them devour their own zooxanthellae, detach and begin life as their own independent animal, soon about to repeat the cycle. Most chiropedes are herbivores and feed on photosynthetic flechtoids, which is probably where they acquire the photosynthetic cells for the next generation from.

In some ways this bears similarity to the reproductive cycle of the unrelated skolex, but in them the sessile stage is diploid and the mobile one haploid, making them alternating generations like in earth-plants, whereas in the chiropedes both forms are diploid. The difference can be understood in simple terms as follows: If you were a male human and reproduced like a skolex, your sperm cells could undergo mitosis by themselves and become independent organisms once released. If you reproduced like a chiropede instead, it would be your whole penis detaching from your body and becoming independent.

While this seems extraordinarily alien, it is really not much different from the reproductive cycles seen in our own oceans’ cnidarians. There, free-floating jellyfish fertilize eggs, which hatch into a planula larva. Said larva attaches to the seafloor, becoming a polyp. As it grows, the polyp produces more jellyfish in a process called strobilation. Some parasitic flatworms, the cestodes, also reproduce through strobilation. The chiropede clade thus derives its scientific name, Strobilata, from this well-known process.

The existence of Strobilata poses a lot of phylogenetic questions for the Chirorbita. Some studies suggest that the clade might actually be paraphyletic, chiropedes being the ancestors to the more derived euchirorbites, like the spectacled chirorbite. If true, this would mean that strobilation is actually ancestral to the clade but was lost later on in some lineages in favour of a more direct reproduction. This is supported by the fact that some of the more basal pseudarticulates (though not all of them), like the menamin, also reproduce through cestode-like budding.

For the family tree of the Fractaria phylum as a whole, other fascinating possibilities open up. It is generally thought that pseudarticulates and polyfractarians, which are clonal colonial organisms, are only distantly related, sharing a common ancestor among simple, monovexillan fractarians. But two new competing schools of thought have appeared in recent years. One proposes that the pseudarticulates actually derived from polyfractarians whose gonosphores became independent from the whole organism. The second, more popular one, is that polyfractarians derived from a basal strobilating pseudarticulate whose organs one day stopped detaching from the polyp and instead started working together as a single sessile organism, eventually losing all complex traits like eyes, guts or a nervous system in the process. Actual evidence for either position has not yet been gathered.

On a final note, it is interesting that, while still attached to its polyp, a chiropede still has a nervous connection to the polyp and the surrounding chiropedes. One wonders how it must feel like in the final stages before detachment, when the chiropede already has eyes and is wriggling, to be your own being and yet still be part of a larger one. If your hand could think, what would it think?