|Accelancea lactininium (Donecinian)|
Nitronea is the common name for a class of extinct boneless Theian life, scientifically named Nitronealia. They are the sister group of the Exotesta, who unlike Nitronealians have a mineralized exoskeleton. They were a unique evolutionary class on Theia, being the first major predators, with a number of Nitronean species becoming the only organisms for millions of years within the animal kingdom to have an instrument (a mineral "tooth) to attack prey with, alongside large, powerful "antennae" to grab prey; as a result, becoming one of the only boneless predators on the planet, and one of the most dominant forms of life in the early-to-mid Creviterozoic eon.
Living only in the sea, they lack the ability to survive in fresh water, which was one factor in their extinction. No species of Nitronea can survive for prolonged periods outside of water, and only one group has evolved a method to do this, allowing it to for a few hours outside of fully aquatic environments; Fonitronealini.
In terms of body structure, Nitronea species could grow from small to large body sizes, the oceanic environments they resided in rarely hindering their evolutionary growth over millions of years, and as a result, some species (such as Magnatronea maioria (Silent Skies)|Magnatronea maioria) could grow as large as five meters in length (from the tips of their grasping appendages to the lower body), evolving to become extremely proficient and voracious predators.
At the time of their extinction in the early-Caliceous following the Dilovian-Caliceous extinction event, most Nitronea were usually defined by their soft body, having no bones or cartilage to build a body structure off of, and their long, grasping appendages (or antennae), which they used to hold and constrict their prey before consuming them through their mouth parts, usually a mineral tooth with a hole leading to the gut, or a long proboscis which they used to pierce other species constricted by their appendages. Other Nitronea however fed on algae-like microorginisms, with their tooth being adapted to simply be a large structure that allowed the algae (and other nutrients) to flow through into the gut to be metabolised, water being filted through "gills" at the side of their body. An example of these "herbivorous" Nitronea would be Tarubula rubidus, with a large "tube-like" structure that flowed directly to the stomach that allowed food to be directly swallowed.
In terms of locomotion, there are a number of ways Nitronean species propel themselves, the primary method just prior to their extinction having been undulating locomotion, using an oscillating thin film of skin (also known as the "fin") running along the mantle of the animal, able to propel itself through the water in a similar fashion to modern cuttlefish. However, unlike the cuttlefish which uses a gas-filled shell (the cuttlebone) to maintain buoyancy, the Nitronea species used a swim bladder similar to many modern fish, using their system of veins to transport oxygen (and other gasses) to the organ as to easily regulate their buoyancy and remain stable. Several groups, had, however, adapted this fin to move in different ways.