Planuslimaxia

Bottom to top: Planuslimax, Velocilimax and whale planuslimaxid

An ancient phylum of flat-bodied aquatic invertebrates found on Elonios. The vast majority of species are detrivores, ranging from just under a centimeter in length to over three meters. Most are under an inch, the larger forms being remnants of ancient times when the group was far more diverse and successful. They resemble sturdier versions of Earth flatworms and behave like jet-propelled slugs.

Planuslimaxids generally have a flat, thin body. It is smooth and rubbery to the touch. Most species take on a shape roughly resembling an oval, but some are disk shaped and some large species have fin-like projections, most notably the aptly named Whale Planuslimaxid, largest of the phylum at ten feet in length. All members bear six pairs of small, spiracle-like gills and four rudimentary eyes. The eyes and gills are generally positioned on top of the body, though this varies in some burrowing forms. Jet propulsion is very common in Planuslimaxids, they having evolved it independently from other creatures. Planuslimaxid jet propulsion organs are generally very long and thin, especially in larger deep-water species where they are merely vestigial (many species, especially larger ones, move via paddling motions. A key feature of Planuslimaxia is their mouth design, which is generally a pair of large, muscle-lined openings designed to suck up the seafloor and filter out non-organic particles. Many shallow-water species, however, actively feed on aquatic plants and have small spines on the rims of their mouths to help cut through plant matter. It is because of this mouth design that Planuslimaxids are often referred to as "double-mouthed space slugs" by visiting naturalists.

These are common denizens of the seafloor, where the larger species can often be seen drifting around vacuuming up sand and muck in search of organic particles. Smaller species generally live in the seafloor itself or under cover in shallower waters, and certain intertidal forms for small colonies on algae-covered rocks. In Elonios's early history, these simple creatures were far more diverse and successful. Competition from other marine detrivores like Vermipods and Lumpcrabs has reduced their diversity, with most forms over a foot in length being found in deeper waters. An exception is the Whale Planuslimaxid, which is found in certain warm coastal waters. The massive size this species is known for, however, is rare, as these creatures have many predators.

Planuslimaxids lay huge amounts of eggs on the seafloor, with the young generally hatching a few days to several weeks afterwards. Most species reach sexual maturity in a few weeks but continue to grow for years afterwards, their reproductive viability increasing as they grow. Smaller and shallow water forms are generally fast growing, but the abyssal giants can take a century or more to reach their maximum size. It should be noted that a foot or two is considered large for even the biggest species of Planuslimaxids. This is the size at which the bigger kinds can begin to breed, and their growth slows considerably after this milestone, with most individuals being consumed before they can become truly giant for their kind.