Surtis

A surtis is an exoanimal in the phylum nmusfemuapifa (n-muus-fem-oo-a-pi-fa). Surtises are distinguished by the cartilage (usually broken but sometimes whole) rings which serves as a flexible, basic skeleton.

Morphology
Surtises are recognised by the whole or broken rings of cartilage which run down the length of their bodies. These support the body and act as anchoring points for muscles. Surtises also possess at least one pair of tentacle-like appendages near the jaw-less mouth. Though many surtises are mobile, they do not have limbs in the usual sense but can slither, crawl in a snail-like fashion or undulate their bodies like a worm. The cartilaginous rings protrude out of the bottom of the body as harder 'feet' along which some surtises walk by undulation in a caterpillar-esque fashion.

Surtises are also one of only two phyla in which true eyes have evolved, providing them with colour vision (though this is very vague and patchy in some surtises). As such, they are often brightly coloured to attract mates without standing out to predatory exoanimals in other groups (such as the pseudosterna which rely on highly-developed sonar and smell). Surtises will often prey on one another, however, so some colour camouflage has evolved in many species.

Taxonomy
Nmusfemuapifa is divided into two subphyla:

Nmisapifa
From 'nmisa' (one who moves) and pifa (tube), and commonly called the 'mobisurtises', these are always at least capable of movement even when adult. They also have eyes with good colour vision. They normally resemble their juvenile forms and can be recognised by the more complex cartilage rings which tend to have protrusions (such as those which reach out of the body to form simple feet in the catersnakes) and most or all of these rings are connected at the top by an antispine.

Nmawfewapifa
From 'nmawfewa' (one who stays still) and 'pifa' (tube), these are the statisurtises. These differ from the mobisurtises in that they lack true eyes (though they can determine light from dark) and have cartilage hoops which are either separate or fused rather than connected by a pseudosternum. The statisurtises also develop into fairly still or fixed to a substrate, despite their juvenile form being very mobile.

Etymology
The scientific name for the phylum, nmusfemuapifa, comes from the Nical words 'nmusfemua' (cartilaginous) and 'pifa' (tube).

Out of lore
The common name is in reference to a character from a previous version of Project Pontragolia focused on a storyline. The plot for this was based around the crew of a spaceship discovering four gems which, when somehow combined, produced a planet which was to act as a reserve for fauna and flora collected by the team. One character was an alien who loosely resembled a surtis and was named Sortir, in reference to Pontragolia's original form in which a goblin-like creature called Sortir-Ru collected specimens for a zoological park. Ultimately, both of these versions of Project Pontragolia were dropped for more scientifically-minded versions.