The Sidestripe Aeuna

Order: Xenoselachia

Suborder: Xenothunnia

Family: Aeunidae

Genus: Velocineustes

The sea commands many niches. With the vast spaces of the ocean, there are many types of predators, but some of the most notorious, intelligent predators of the oceans are the aeuna, Velocineustoidea, which are large, intelligent and frighteningly fast predators who have been successful for the last 15 million years. In the equatorial seas, the most common species is the sidestripe aeuna, which is roughly 1.5 metres long and is a close relative to the much larger sicklefin aeuna (Velocineustes falciformis) and is a common sight at seamounts and coral reefs.

Aeuna are some of the fastest predators in the seas, partly due to their rather unusual method of respiration and the method of swimming, which is thunniform. Unlike most other species of pelagys, aeuna possess an 'intake spiracle' in front of their gill pouch that faces forward, designed to intake water when swimming, which directs water into the gill pouch, and then allowing the deoxygenated water to flow out, completing the respiration process. With this passive mode of ramjet ventilation, they can input more muscles into their tail, now having to exert little to no energy to breathe, allowing them to swim at high speeds without tiring for long distances, but with the tradeoff that it has to keep swimming in order to breathe, however it can exert no energy for breathing, and also facilitate intake of oxygenated water, actually taking in more oxygenated water when it swims faster, increasing its stamina. This high speed swimming is due to their method of swimming, which is thunniform swimming.

Thunniform swimming essentially means that all movement is restricted to the latter half of the ophistoma, the tail. This entails a very fast and rapid mode of swimming, as all the thrust is provided by the tail, and the reduced oscillations of the body reduce drag and increase hydrodynamicity by a wide margin. Thunniform swimming is known as some of the most efficient at high speed swimming, and species that utilise that mode of swimming have lunate tail fins and a caudal pecundle to stiffen the tail to allow them to swim extremely fast for long distances, with the sidestripe aeuna reaching speeds of almost 45 km/h at full speeds, however usually swim at speeds of 23 km/h when not hunting prey.

Unlike the grapshark, which can essentially only eat prey large enough to be grabbed by their raptorial mandibles (and is thus extremely specialised for this type of food), the aeuna can expand its dietary palate to small pelagys which practice schooling, making them among the most common predators in the Alladorian seas. The sidestripe is the most common, and can be found swimming near shoaling pelagys and are mostly pelagic, swimming in deep water and occasionally entering reefs when looking for food. The sidestripe frequently swims in shoals of 4 to 5, sticking together closely for most of the time but not sharing much coordination, however also reveal another aspect of the aeuna which is quite unexpected: their intelligence. Aeuna are some of the most intelligent predators in the sea, remembering locations, hunting tactics and even other individuals. Older individuals of sidestripe aeuna often hunt in association with larger sicklefin aeuna, which they essentially communicate to by figure-eight swimming patterns, signalling that food is nearby. Their intelligence does not stop here; they frequently swim together in shoals in order to avoid predation by grapsharks, one of their few predators, and remember locations where grapsharks are likely to ambush them, however, they lack the capability to stand still in the water due to their ramjet ventilation breathing method, and thus are frequently ambushed when careless.

The aeuna are highly diverse, the sidestripe is one of 20 species of fast-swimming pelagys, with the largest species (Kronos's aeuna, Gladiodon ferox), reaching a whopping 4.8 m long and over 890 kg in weight, with this extremely successful suborder, with their intelligence, their speed, their ferocity and strength allowing them to spread worldwide in the seas of Alladoras.