Netchu

Many things live beneath the ground, in the ancient lava tubes of Mars. Often nameless things which gnaw at the roots of the planet, almost literally. Where the air is moist and temperatures are right in these dark tunnels, lithotrophic microorganisms thrive, feeding on ferrous and sulphurous minerals, sheltered from the dust storms and UV-rays on the surface. Where there once flowed glowing lava are now bioluminescent walls covered in a slimy moss composed of areonts and macroarenonts. Their waste is fed upon by pennatophytes and any airborne particles are filtered by sporians.

And where there is flora there will usually follow fauna. One of the more common animals in the lava tubes is the netchu, a rather funny-looking fellow, small enough to fit in the palm of your hand. Its body is an almost spherical cauldron supported by four tube-like legs which end in feet that resemble suckers or upside-down funnels. Atop the body grows a dextrous proboscis with a mouth at the end. The mouth is a simple tube which can extend into a lamprey-like maw, whose inside is beset with rings of little grinding teeth. These the netchu uses the scrape off and feed on the mossy walls. Similar tooth-like protuberances covering the soles of their feet, giving them excellent grip while climbing walls. The netchu has no visible eyes, instead there are writhing tendrils growing out of all the extremities, which the animal uses to feel its way through the dark corners and crevasses. Netchu are largely soft-bodied and capable of almost fully retracting their proboscis and their legs into the body, as can be seen in the right individual. Little is known about their general behaviour, as their habitat makes them difficult to study. Observations during winter time suggest that they survive by entering a deep sleep in which they likely breathe hydrogen, much like other cave dwellers. It is theorized that they reproduce by laying eggs (Schröckert 2301).

 Calyx of a netchu, with vestigial(?) leg bones.

Historically, netchu were grouped with a variety of other miscellaneous Martian invertebrates among the phylum “Brachiostoma”, which has however become invalid. The internal anatomy of these organisms played a large part in breaking up that waste-basket-taxon. Netchu have little in common with any of the Martian worms and, as may surprise some looking at them, actually possess an endoskeleton, albeit a simple one. The body is internally supported by a so-called calyx or test, superficially similar to what is seen in sea lilies or sea urchins. It is a bony box which encases the internal organs and offers attachment points for muscles. Unlike in echinoderms or vertebrates, this skeleton is only rudimentary. The calyx is open on top, allowing for the complete retraction of the proboscis into the body. The legs are supported at the base by single tiny bones articulating with the calyx, which serve solely as muscle-attachments, leaving the rest of the limbs soft-bodied as well.

Where that puts the netchu on the extant Martian family tree is a much-discussed question. The presence of an endoskeleton may put them somewhere close to the onychognaths or the trichordates, though the similarities are superficial at best. Similarly to the zitharta, some have taken the position of the cloaca, which is atop the calyx close to the proboscis, as a trait that might unify them with the Antitremata. This simply seems to be a case of convergent evolution, however. As in Antitremata, the posterior or ventral part of the body is internally sealed, albeit by the calyx in this case, forcing the gut to wind back up to the top to find an exit.

Out of extant animals, their internal anatomy instead puts them closest to a group of small bipedal surface animals called Craniopoda, to which belong funny fellows such as the utigog, tila and ganguar. These were previously classified as highly aberrant nothornithes or simply as incertae sedis, but their apparent relationship to the netchu and similar forms has opened up the opportunity of classifying them as their own distinct phylum. This new clade has been given the name Hemicalyxia. Of course, that still leaves open the question of their wider relationship status. Based on morphology, the closest relatives of the Hemicalyxia may have been the ancient Ambulostellia (Sivgin 2345), a phylum that is now thought to be completely extinct on Mars, being only known from fossils. Both may form a larger superphylum with the trichordates (Bomhoff 2340). If true, all three phyla seem to have descended from a radially symmetrical ancestor, distinct from the laterazoans (and without going first through a bilateral phase like Earth’s echinoderms). Though in Hemicalyxia we can observe a late bilateralisation, with basal forms like the netchu reducing their legs down to an even number and moving with bilateral behaviour and more derived forms like the craniopods becoming true bilaterals.

References:

• Bomhoff, Nils: A common, radially symmetric origin for the Hemicalyxia and Trichordata and the erection of the new superphylum Xenoradiata, in: Astropaleontology, 528, 2340, p. 85 – 101.
• Schröckert, Daniel: Fortpflanzungsweisen der marsianischen Brachiostomen, Bochum 2301.
• Sivgin, T.K.: Life on a Dead Planet. The first 3 billion years of Evolution on Mars, Zürich 2345.