Dwarfs have big eyeballs and stay tiny (go figure).
Briareus have a constant blue-green iridescence and red mottling. Very long legs and extensive webbing, like an umbrella. Generally smooth skinned but can have minimal texturing.
Aculeatus generally are sandy brown with black markings, also sometimes solid black with a white stripe down their mantle and "face". They can also invert their color scheme to white with black markings. Very long legs. Texture is usually algae-like, rarely smooth.
Hummelincki and Vulgaris both look pretty similar, large stocky mantle with shorter stouter legs. Hummelincki have the distinct blue eye-spot underneath their eyes, Vulgaris do not have the eye-spot. They are both very capable of a variety of color and texture changes.
Bimacs are less common these days and are cold water species. They also have the blue eye-spot like Hummelincki but are generally not as heavily textured, could be confused with Hummelincki pretty easily.
All of which can have a brown coloration when at rest, like a few dozen other species of octos. These are just the ones you will typically find in the trade currently.
