As far as the universe goes, there are many species out there, and probably many more to discover. This is a list of the ones we know of so far. (Species names are a WIP, please check back later when they are finished!)
Canis Majorus are essentially what's on the label- large, dog-like creatures, who inhabit a lot of the more urban environments of the universe. However, they can survive just about anywhere, being hardy enough to not get too unwell from pollution. Most Canis Majorus tower over anyone of other species, standing well over 6 or 7 feet, equipped with tough, claw-like fingers and sharp fangs. Canis Majorus are carnivorous, and much of their diet is made up of meat- too little meat in their diet will cause problems for them. Due to their size, hardiness and general stereotype for stubbornness, Canis Majorus are often put in charge of other species, whether they want to be or not.
Smaller Canis Majorus, such as Sanford, tend to be toward the bottom of the hierarchy, while bigger Canis Majorus stand at the top. Those at the top are more ruthless to everything they see as beneath them.
The second-most hardy species, [species name here], can be found in most environments, though do not thrive in fully urban locations like the Canis Majorus can. While omnivorous, most prefer a more vegetarian diet, a diet a lot of urban planets do not facilitate as well as suburban or more natural planets, so most tend to stick to these environments.
Several notable features of [species] is their resemblance to bovines, cervids and other horned ungulates, with hooved feet and hooved hands (though some may have paw-esque hands). From long, upright horns like a gazelle or antelope, to curved, swirling horns like a ram, to even the sleek antlers of a deer, this species' horns or can encapsulate all types. They grow slowly over the course of a lifetime- larger horns can indicate an older [species], if the horns have not been damaged. Most damages the horns can grow back from, and most [species] expect their horns to be chipped or break once in a while- it is painful, but they expect it. However, if the horn is burned in any way, while it will not visibly show marks unless cut, it will stop growing. Some [species] will use this to mark 'unruly' or 'outsider' members of a group, others may just be unfortunate enough to be caught in a blaze. The horns are not their only defining feature though- most members of the species have long fangs, like a water deer or tufted deer. These normally stick out of the mouth, though there may be some whose don't. If they are broken, they don't grow back.
The fickle and isolated [species] are generally hard to find in a lot of locations due to the lack of proximity to water. They thrive with water, and tend to not do so well without it. The species has split into two subspecies to deal with this though, the deep-water aquatic [species] and the 'landbreathers', the terrestrial [species]. The two subspecies can and will coexist, though in some areas the aquatic subspecies, being the 'first' subspecies, will try and drive out any terrestrials.
The main difference between the subspecies is habitat- aquatics stay within the deeper parts of the water they live in, while terrestrials stick mostly to land- though they can enter water, and aquatics can enter land. Due to this, they have both lungs and gills, hidden under thick but light waterproof fur that coats their head and possibly the back or chest too. In water, communication is done through biolumiescent 'horns'- the larger and more elaborate the horns are, the higher up in the hierarchy of [species] the individual is, and to guide them each [species] individual has a tail akin to an aquatic animal of any species, from sharks to seals to things such as stingrays. Where both subspecies differ, however, is colouring and eyes- aquatic [species] have primarily dark and neon colours to help find each other in the lower light of deep waters, and neon-coloured eyes better adapted for low-light conditions, while terrestrial [species] tend to have a more varied range and eyes more like those of the other species. The two subspecies cannot mix in colouration naturally.
The reason [species] are so rare to find outside of their own natural habitats is sensitivity to their environment- if the environment is off in any particular way, it can start to make them sick, dulling their colours, leaving their horns brittle and prone to damage, and will eventually kill them. Where they grew up is normally where they stay, though due to their nature of being on land, terrestrials can be in more places, as long as the environment still fits a range of right environments. Tropical-borne [species] like Azurite or Veilei prefer warmer temperatures, and are very susceptible to freezing in the cold, and clean-water species will get more sick in sunken urban environments than those who have grown up in those 'polluted' waters. Taking a [species] out of the wrong environment will allow them to recover, though the process tends to be slower than the onset of illness.