Wanderstalk

Striding on its roots

There comes the Wanderstalk,

not wearing any boots.

It does not like to talk

It is not yet a plant

And neither a zoon

It trotted on top of the sand

Which it liked to grow on.

Striding on its roots

Thereon, as stiff as a balk,

not wearing any boots,

there goes the Wanderstalk.

- Müslüm Zohra, Martian Poems, 2285.

When first approached, wanderstalks may appear to an unwary astronaut to be ordinary species of shellubim. They are seemingly sessile organisms, or “planimals”, firmly anchored into the ground by long stalks. Their soft body is protected by a hinged shell, out of which they extend eye-stalks and leaf-like fleshy wings, which photosynthesize enough to fuel the organism’s resting metabolism. But when startled, these organisms have a trick up their sleeves that their sessile cousins lack. They can simply emerge out of the dirt and walk away on crustaceous legs. Wanderstalks are in fact not shellubim, but terrestrial relatives of the amstiels. Most fossil and genetic evidence suggests that they represent a second invasion of land by this basal grade of antitrematans, with endosymbiotic photosynthesis in both being a case of convergent evolution.

And it seems the wanderstalks may be slowly winning their race to land, for they are far more widespread and numerous than the shellubim. They can be found in nearly all habitats, though are especially common in the southern highlands and other elevated regions, whereas shellubim are only common in the northern lowlands and the Hellas Basin. The most likely explanation lies in the atmospheric development of Mars. Shellubim are sessile as adults and reproduce through pollen-like gametes and small mobile larvae which fly or even freely float in the air as aeroplankton. As the fossil record of these organisms suggests, this used to be a very successful strategy early in the planet’s history due to its low gravity, but as global air pressure declined, staying airborne became increasingly difficult, hindering reproduction and also leading to a large decline in the aeroplanktonic ecosystem that adult shellubim fed on. Thus, they are now largely restricted to lowland regions, where air pressure remains higher than average. Wanderstalks meanwhile remain mobile and grounded their entire life and reproduce directly. Much like their aquatic relatives, two individuals simply walk up to each other and mate. The developing young are then either deposited as eggs into the ground or are carried inside the parent’s body, but in both cases come into the world as miniature adults able to walk and live on their own. It is likely that the even more numerous skolex evolved their particular mode of reproduction for similar reasons.

Wanderstalks also do not rely on microscopic aeroplankton to feed. Their eye-stalks double as muscular tentacles, in some of the larger species are strong enough to break an astronaut’s finger (yes, this is based on someone's personal experience). Through a combination of bright colours, foul stenches, sucrose secretions and/or even venom, wanderstalks attract, grab and kill smaller wadjets, which they feed on inside a closed shell, using a pair of mandibles comparable to what is seen in the zhor. In at least one reported case, a yateveo was even observed feeding on the proboscis of a poor ptannu (a tundraic species of bennu) that had unwisely stuck its beak into the wanderstalk’s shell.

Wanderstalks also have the advantage of migrating towards suitable habitats when necessary. Most of the ones living in the tundraic southern highlands in fact do, following the wadjet swarms into the northern shrublands and the Hellas Savannah when winter makes the South nearly uninhabitable. The intriguing thing about this is that they migrate in remarkably straight paths, suggesting they have an innate sense of distinguishing between north and south. How they do this is not yet known. Mars has no global magnetic field which these organisms could exploit in the same way as migrating birds do on Earth, only localized hotspots created by magnetized ancient crust.