Introduction to Dissilmorda, or the Ragfish
Literally meaning ‘spring bite’, Dissilmordids are the most successful group of Aquila’s ragworm descendants. Known informally as Ragfish, the past hundred million years has been kind to these spring jawed aquatic horrors.
Dissilmorda is one of the most diverse phyla on Aquila, surpassing 15,000 documented species. Ranging from tiny creatures barely larger than tadpoles to 15 meter long monsters with crushing mandibles, and from sea serpents covered in lateral razorblades to lazy ambush predators that bury themselves in the sand. Whilst invariably unpleasant in appearance, not all species are predatory. Some use their extendable jaws to clip off clumps of vegetation, or delve deep into carcasses to reach meat that other detritivores cannot exploit.
Dissilmorda is distinguished from its relatives by its extendable jaws (Although some very large species have lost this capability), highly developed mandible sheath, and structure of rib like rings and ventral column supporting the animal’s weight. They also posses highly developed gills, with water pumped in and out by lateral movement as the animal swims. In particularly advanced species, water is pumped in and out by the inflation and deflation of the gill sacks, like an underwater lung.
Ragfish made several innovations early on in their evolution that allowed them to outcompete their ancestors. One key factor in their early success was the efficiency of their feeding mechanism. Modern ragfish feed with spring loaded, extendable jaws, that shoot out to grab prey that’s just that little bit too quick. The structure that once hid the jaws of their ancestors is now a hydrodynamic outer sheath that opens like some kind of nightmarish flower. Such animals now make highly effective predators, either lying in wait or chasing down their prey, their spring loaded jaws halving the effort of the hunt.
Probably the biggest advancement of modern ragfish over their ancestors and their cousins is the development of a complicated, rib-cage like exoskeleton. Unlike their ancestors, their exoskeleton is not jointed and segmented, but made up of a reinforced rings, supported by a ventral chord based around the animal’s original joints and the protection of their ganglia. Between these ‘ribs’, flexible chitin forms a covering analogous to a rubber-like ‘skin’, dramatically reducing the animals weight whilst improving the efficiency and flexibility of the animal, without sacrificing much in the way of structural strength. Such a structure was necessary for early ragfish, who needed speed and manoeuvrability to escape their ancient predators. Like the jaws of their ancestors, the rings of a ragfish exoskeleton are formed from a very tough, lightweight material. This is mineralised not with calcium, but from a histidine rich protein, with bound zinc ions. Indeed, this material has been used to construct components of lightweight exoskeletons used by human settlers. This exoskeleton, rather than requiring a moult that would leave the animal particularly vulnerable, simply flakes off in small pieces as new chitin pushes up to replace the old.
Their predators also provided an evolutionary imperative to change another physiological handicap of many invertebrates. Ragfish no longer possess an open circulatory system. In order to escape predators, such a method of oxygen transfer was simply not efficient enough. With time, particular pathways through the bodily tissues became dedicated because they provided faster movement of blood through the body and back to the heart, making these early creatures increasingly quick and agile. With time, blood vessel analogs developed to maximise the chances of outrunning predators.
These advancements were critical to the success of Dissilmorda, and have allowed an incredible diversity of form to arise, as well as allowing some genera to reach truly monstrous sizes.
Although some of Aquila’s scientists have been tempted to classify ragfish as some form of ‘neovertebrate’, this classification does not hold up. For one, the skeleton, although dramatically reduced and far more efficient, is on the outside of the animal’s body, derived from their ancestor’s external cuticle. Secondly, although ragfish may appear to possess what appears to be a ventral ‘spinal chord’, this is little more than a section of reinforced joints held together by muscle and chitin. It does not contain the ganglia like an actual spine would, but merely serves as a point of extra defence, and a support column for the rest of the exoskeleton.
This particular species, know as a Rakul, is a typical example of Dissilmordid success. At just over three meters long, it is around the size of a mako shark. most of its chaetae have become lateral defensive spines, while its front two neuropods now closely resemble the pectoral fins of earth fish, and serve much the same purpose. An active predator, its two front eyes provide decent binocular vision to zero in on fast moving prey, while its two rear eyes keep watch, for larger monsters lurk beneath the waves.
Iphone photo. Again. Ink and watercolour, on mount board of all things, works surprisingly well.
even if the two creatures inhabited the same planet (which they don't), they would be ofshoots of very different branches of their tree of life. of course, all lifeforms on one given planet ultimately come from the same ancestor, but you'd have to get to a time equivalent to terran cambrian explosion (or even further back) to find the common ancestor of these two.
look at it this way. before the ancestral "worm" had any sort of limbs or eyes, it sure as hell had a mouth, so the mouth was the first thing that differentiated, in fact, a very important role in this early differentiation on earth was which end of this "worm" ended up being the head in the first place (that's why we have protostomes and deuterostomes), that being the case, if you get mouths that are so radically different, it's instantly obvious the two creatures cannot be closely related.