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?

Spectacled Chirorbite

Chirorbites are likely the most derived members of the superphylum Pseudarticulata. It was first believed that pseudarticulates, despite their unusual morphology, are members of the Martian animal kingdom, as they are heterotrophic and mobile, at least at some point in their lives. This assumption turns out to have been wrong.

Having already met animals that behave like plants, it should maybe not come as a surprise that on Mars there are also “plants” that behave like animals. It now seems clear that pseudarticulates are unrelated to Arezoa, but instead are deeply nestled within the Fractaria, a kingdom which otherwise only includes immobile organisms with no nervous system that live autotrophically or through passive filter-feeding. The commonalities are not only evidenced by their characteristic glide-symmetry but now also molecular data.

Pseudarticulata likely descend from an aquatic ancestor not too different from the frondomorph monvexillans in the foreground. These organisms originally were sessile autotrophs, filter-feeders or osmotrophs their whole life, their chiral body-isomers being constructed of ciliated filtering-chambers and held up by a hydroskeleton. While it is effective for such a lifestyle, such a bodyform is restrictive when wanting to develop more complex morphologies and behaviours. The majority of Fractaria have worked around this by opting for a clonal, colonial lifestyle, such as the two organisms seen here at the back. This represents a path of increasing complexity through external compartmentalization. Pseudarticulata on the other hand went down the other path, the one of internal compartmentalization. Their ancestor must have been a single frondose-organism, which, instead of being anchored straight on the ground, lied flat on the sea floor with its leaf-surface and was capable of crawling across it using cilia, likely using the filtering chambers at the bottom surface to feed on algal mats, while those at the top became specialized in respiration. The former holdfast, now being the first thing that comes into contact with the world as the body crawls forward, soon began being studded with sensory cells, the beginnings of encephalization.

Organisms such as the Spectacled Chirorbite represent a major improvement on these primitive beginnings. Out of sensory and contracting cells, already present in the earliest fractarians, has now evolved a nervous system, with muscle-tissues to control, evolved completely independently from the Arezoa. The small channels which used to connect the chambers of each isomer have become a true, zigzagged through-gut. The formerly gelatinous body is now covered in a tunicine exoskeleton. The chambers at the bottom sole of the body have given up their digestive function. Instead, they now house hydraulic tubefeet, evolved out of extensions of the hydroskeleton’s mesenteries. Instead of cilia, the Chirorbite now uses these to walk and can also fully retract the tubefeet into their pores, much like a starfish. The primitive cephalon has become a proper head segment, housing little tasting, smelling, and hearing feelers and, most conspicuously, eyes. Underneath lies a crescent-shaped mouth with two hardened lip-plates. The chirorbites use this shearing-structure to feed on low-growing vegetation, including their botanical cousins, as well as very small trichordates, spirifers and onychognaths. Its most common prey is the Menamin, which is also a pseudarticulate, but worm-like with no exoskeleton and limbs.

In perhaps a twist of irony, chirorbites are among the few Martian organisms, along with aspiderms, to have evolved liquid-filled lens-eyes, not unlike yours or mine. These eyes, usually five of them, are covered underneath a translucent tunicine window of the exoskeleton. For unknown reasons, the chirorbite also seems to have eyelid-like membranes underneath this hood to close its eyes. It is funny how an organ this basic can generate much sympathy as Man interacts with his fellow alien. Looking at the Chirorbite’s face, one may feel like catching a glimmer of consciousness, perhaps even a soul, behind those eyes, which one does not perceive when looking at the inanimate compound-eye of an arthropod. Yet, the “brain” of the Chirorbite is a ganglion the thickness of a lentil and it is confronted with minds that are as distant to its consciousness as its is against the vegetative relatives it feeds on. An intellect, which is as vast as it is cool and unsympathetic, now rears its malevolent jaw apparatus into the picture, leaning on avipodous legs over a chirorbite, helpess after it had been turned onto its back. The polychaete-like grin of the rannu is made all the more sinister by its maw having no eyes to speak of, just four black holes representing the nostrils and earholes. Man is unfortunately more likely to find his equal among the stars in such minatory beings.