Áros (plural hóuros, following Nébran grammar) is a cephalopod distantly similar to Etéran coleoids, though modern taxonomists believe it to be a case of convergent evolution. They're the only surviving representative of their subclass on Tebríth. Houros used to inhabit areas quite distant from Tebríthan civilization, and have been discovered relatively recently, thus data about them is spotty.
Much like coleoids, houros posses a bilateral symmetry, have a closed circulatory system, gills, a mantle, a beak and some other similarities. However, they also possess significant differences.
Visually they're easily distinguished by having six limbs and four eyes. Their skin's ability to change colour is rudimentary compared to octopodes, only allowing very coarse camouflage that is near-useless against sight-primary predators. Likewise, they lack ink cloud glands. An adult aros masses about 5-10kg.
Originally, the species was found in swamps, rivers and lakes of Tebríth. Preferred salinity is less than 3%, but short-term survival in saltier waters is possible. Depending on air moisture levels, an aros may spend up to 20 hours ashore without risking its health, which is important for migration during dry seasons. Land movement is rather slow, but not something houros shy away from. Currently, all surviving houros are held either in nature preserves, or as pets. While, demographically speaking, they're a species on the verge of extinction, their de facto legal status and treatment varies by jurisdiction due to various technicalities.
An aros' neural system is remarkably centralized compared to Etéran coleoids: it fully understands and controls the positioning of all of its limbs, though isn't as good at multitasking manual actions. The neural system keeps undergoing development throughout all life, and the largest specimens seem to demonstrate intellect comparable to those of dolphins, chimps and the like. Nonetheless, cognitive differences make a direct comparison difficult. One more note on neurology: under normal circumstances, the houros don't need sleep at all; they do however significantly shut down their neural activity when undergoing hybernation (which they rely on for surviving inhospitable seasons).
The species' eyes do not detect light polarization, but are fully colour-sensitive. They have good night vision and see equally well in the air and under water. An aros can either focus four eyes on a single object, or keep the central two eyes facing forward while using the other two to maintain a 360° (or nearly such) field of view. All eyes are covered by transparent nictitating membranes.
Houros are nearly deaf, barely distinguishing environmental vibrations.
For hunting as well as for detecting larger predators in murky waters, houros use electroreception, much like platypodes and some sharks do. In the air, the sensitivity is significantly compromised. Still, these animals tend to pay special notice to things with significant electrical fields, such as many modern gadgets.
Much like the octopus, the aros has chemoreceptors on its limbs, and can taste things by touching them with its tentacles. While the species is omnivorous, individuals can occasionally develop preferences for some foods and dislikes of others. The digestive system lacks any venom glands or symbiotes serving similar functions.
The aros' gills are quite adaptive, being able to function in air for many hours, so long as they haven't dried up. Houros possess special reservoirs for storing water precisely for this purpose. Some amount of oxygen is also absorbed directly through skin. Due to all these factors, staying ashore for a day or more risks rapid dehydration once the additional water reserve is used up.
The species' reproductive strategy is quite unusual compared to Etéran cephalopods: they're parthenogenetic sexless K-strategists (relatively speaking). A brood is usually made of 3-6 offspring, and brooding is a rare event, triggered by unknown factors. The offspring are produced by a fission-like process, and spend the beginning of their lives in the water reservoirs. They start of massing less than an ounce, but grow to adult size in a matter of months (faster or slower depending on the availability of food and other conditions).