Jetgiller Anatomy

Meet the Jetgillers (Pulmonobranchia), the closest kin of the pelagys, yet still wildly different.

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The pelagys are not alone in the seas of Alladoras. Stranger, potentially even more alien creatures share their oceans with them on equal footing and niche. Meet the jetgillers, the jet-propelled distant cousins to the pelagys.

At first glance, they look nothing like pelagys. A strange beak for an upper jaw, a pair of lower jaws, three long tongues, a body with long gill sacs, the jet-lungs, a pair of dorsal and ventral fins which are used in paired-fin swimming and finally a thin tail. However, despite this, they are from the same stock as pelagys, and have diverged over 450 million years ago, meaning that they have evolved independently in various strange ways.

Evolved from a strange, octopus or squid-like species with a similar beak which evolved over 450 million years, which explains their divergence from pelagys, which are quite distant, they have developed their jet propulsion from their jet lungs, which allows them to scoot away at rather high speeds. Their rapid evolution allowed them to be the dominant species, in fact, for around 300 million years, in which a mass extinction event eradicated much of their species, allowing pelagys to rise up and take centre stage, but the jetgillers are not down for the count; they are still going strong, still a very successful group, even recovering from one of the worst mass extinction events in the history of Alladoras.

Built with a fusiform build (tapered at both ends), they are quite hydrodynamic, and with their jet-lungs, they can blast away at high speeds consistently, making them among the fastest species on Alladoras. And those jet lungs? A very strange, enlarged pulmonary sac which has an intake spiracle and exhaust, which allows them to suck in water into a highly vascularised region, enriching their muscles with precious oxygen, allowing them to sustain rapid and constant activity. To facilitate this, their hearts are specialised and almost wing-like and twice as efficient than most pelagys, granting them immense speed and stamina; some larger species have hearts that beat so loudly they can be heard 3 metres away from one. Aside from their jet propulsion, they can use their fins to propel themselves, albeit much more slowly.

Their jaws are rather strange too. Their two top jaws have ossified, like pelagys, but now support a beak-like structure known as an operculum, however, the lower jaws have stayed largely unchanged and aid in protecting the three, long tongues that they use for gathering tactile sensory information and for food manipulation, which often have setae or teeth for feeding.

However, they still come from the same stock as pelagys, but still rather different. Firstly, their ribs are similar to pelagys gill arches, and just like pelagys, also developed themselves into the skull. Jetgiller skulls are rather similar to pelagys, and their jaw structures are very similar. Their limb girdles are also similar to pelagys, but are ultimately different structures derived as well from the rib structures. Ontogenetically, their embryonic stages are also very similar, sharing features with their ancestors, the gillbacks, most specifically their larvae. Internally, their organ systems are very similar, like their blind-guts and nervous system. However, they do have their differences, like their 'oil sac', which aids in buoyancy (pelagys have a similar sac but with ammonium chloride instead).

Despite the fact that they have been nearly entirely eradicated in an mass extinction millions of years ago, they are still going rather strong. They are still extremely diverse and have a worldwide distribution, just like their distant cousins. With large species such as the filter-feeding gallant rusher (Calcarostris velox), the fearsome predatory murazha (Temnotelum posaidonus) and stranger species like the lopsiders (Asymmetridae), they are still a very diverse group. The species here, a pipsqueak darter, is a small carnivorous species that feeds on crustaceans and is a common benthic schooling species in carpgrass. Most of their relatives are not social like them, and stick to the sea floor feeding on worms and other soft invertebrates.