Aquarians are androgynous humanoids, slightly smaller on average than humans, mesomorphic but with strong core and oblique muscles, and a thin layer of dense, fat-like cells just under (or less commonly, over) their skin. They have varying skin colors and patterns, generally tropical blues and greens with gold or red spots or stripes. Their heads are topped with a semi-translucent whitish filament, which they can also sprout from other regions of their body to form silk clothing-like protection. The filament can be injected with digestive enzymes or reproductive materials.
Aquarians utilize photosynthesis, but in most climates require nearly as much food relative to their size as humans. They are omnivores but lean towards vegetarianism. They can reproduce both sexually and parthenogenically. Their brains consist of three highly redundant lobes, each taking on a slightly different personality, and the lobes sample information and generate neural activation patterns competitively, to bootstrap learning. While biological sex exists in a manner similar to humans, they have little sexual dimorphism. On the other hand, gender is continuous and triangular, based on the average contribution of each lobe to that individual's behavior, but these distinctions are often too subtle for non-aquarians, and generally not important to aquarian society.
Procedural and semantic memories are passed during reproduction. Episodic memories are also passed, but are generally scrambled and dream-like, except in cases of parthenogenesis where the offspring is a full clone. Offspring reach full physical/sexual maturity within 2 years and given the way memory is passed, can survive independently from that point on. However, they require large quantities of food and remain child-like in personality up to around 7 years old. They have short lifespans, averaging around 50 years under ideal circumstances. Except when necessary, most only reproduce once or twice in their lives, often once in mid-life and once towards the end of their life, with a preference towards parthenogenesis, generally only engaging in sexual reproduction once every few generations.
Aquarians are egalitarian and socialist, lacking an innate sense of or desire for hierarchy and power. They fall naturally into suitable roles, take a functional detachment towards interpersonal conflict, and even in cases where executive leadership is necessary or efficient, these roles are seen as necessary burdens rather than privileges.
Aquarian biology is inefficient, and aquarian society interdependent. They struggle in isolation or under conditions of extreme physiological adversity. However, as a society they are far greater than the sum of their parts, and the individual aquarian benefits from their society in a way that makes them often seem superior to their human counterparts. Humans and the other intelligent species find them threatening, not just because they are the only species that seems to be thriving, but also because their society and psychology is seen as a threat to the powers that be, and because they have no qualms with stating these facts plainly. They are not arrogant or malicious, and can engage in social politics, politeness, or other niceties when necessary, but generally don't see the value in doing so, arguing, perhaps rightly, that the other species would be better off doing likewise.