The Hoodmouth Plaguefish

Order: Parasitopteriformes

Family: Hirudoichthyidae

Genus: Hirudoichthys

Large pelagys. such as gallantee, tutel, grapsharks among many others are more often than not plagued by a variety of parasites. Their size means they are a suitable candidate to be a host for a variety of parasitic organisms. From external parasites that feast on either blood, the skin or those who burrow through the flesh itself to endoparasites that plague the pelagys from within. Such insidious creatures have developed so much for their specific parasitic niche that they sometimes look nearly unrecognisable to their relatives. And some parasites may pose a much bigger risk than what they might seem.

Enter the hoodmouth plaguefish. This, strange and somewhat flattened pelagys is the most common in its clade, the hirudoichthyids, a family of parasitic species most closely related to the skiparees and their symbiotic relatives the stickyfins. However, these two clades have been split over a period of around 30 million years or so, and look vastly different from one another. Plaguefish are very strange. They have tiny eyes that have relatively poor vision, large, poorly ossified jaws that have been reduced to 4 large, sort of 'tentacles' that cover its pharyngeal jaws, which now act as a rasping beak. The entirety of their underside has a variety of folds and little spurs that allow it to stick onto surfaces, most often than not large pelagys such as gallantees. Their bones are very poorly ossified and their limb girdles being highly reduced, These primitive traits may call back to the early relatives of pelagys, with their tentacle mouths and similarly cartilaginous bodies, but the plaguefish are simply neotenic and retain several atavistic traits, such as the lack of proper ossification in their jaws; it makes them perfect to feast onto larger pelagys without having to use much energy.

Most often found on larger hosts, the hoodmouth plaguefish often swims slowly over the seafloor if it does not find a host. Typically, it uses its sense of smell to find its host; large chemosensory appendages within their mouths allow them to smell for prey. Once they find a host, the hoodmouth promptly attaches to its flanks and begins rasping into its flesh. Their beak-like pharyngeal jaws are easy to underestimate; they are small, but they do a frighteningly good job at tearing through skin and flesh. During this process, they release a saliva which helps break down the flesh further, but also numbs the pain so that the pelagys will not notice. Once they have dug down to a suitable layer, the hoodmouth releases an anticoagulant fluid which stops the blood from clotting and allows it to leak profusely, drinking as much blue, copper-stained blood from their hosts to their heart's desire; they can stay on a single host for several weeks, moving to different regions. Hoodmouths and other plaguefish which share its lifestyle are not fatal. At most, they cause irritation to their host; but in larger quantities they may be more than just an irritation; it may prove to become a significant health issue for the pelagys. Plaguefish may also deliver harmful diseases and pathogens through their saliva into their hosts similar to mosquitoes, and the wounds that are left from their feeding can get infected.

This only counts for the females of the plaguefish, however. Only the females are in fact, hematophagous parasites, and the males are much, much smaller, an extreme case of sexual dimorphism. Plaguefish are virtually identical as larvae as they feed on plankton among other things, but as they grow, the females become much larger, fatter and eventually become parasitic, but the male plaguefish only grows somewhat bigger. After they reach adulthood, they grow larger sensory organs; their oral chemosensory organs become much larger and are used to detect the female's pheromones and their eyes become grossly enlarged so that they find females much more readily. After they reach adulthood, the males lose their digestive systems too, their only purpose reduced to simply finding females to mate, and if they find one, they promptly breed and the male may die soon after. Such strange strategies for reproduction originate from the fact females have become way too large to move around to find males and have become nearly dependent on sucking on their host's blood for survival so the males simply have to find mates themselves, sacrificing their ability to feed just to pass their genes onto the next generation.