Ecology

You can divide life into roughly four common categories: plants, mixotrophs, fungi and osteoderms.

Plants

I am typically saying plants, because they are autotrophic photosynthetic non-mobile spermatophytes that root in mostly broken down dead material (soil), absorb water and organic elements from it and often act as the bottom of the food chain. However, they are biologically a lot closer to fungi  and don’t exactly grow like “plants” on Earth.

Firstly, the plants that fall into the typology of woody plants (trees, shrubs and anything that need to not be floppy) sort of have bones. They grow a central and extremely dense fibrous core to their trunks and branches, a layer of fleshy succulent tissue around the core and a leathery translucent skin protecting from the environment. They are probably most similar to cacti in structure.

Thorns, surface toxins and purposeful hosting of pest eating animals are very common methods for larger plants to defend their soft tissue, since eating the trunk is easier than it is for Earth trees. It is still mainly the ability to regenerate soft tissue damage pretty aggressively that keeps them alive, even if most trees do not live as long as on Earth.

Large plants also have a powered circulatory system. They do not really have hearts, but a series of decentralized valves and the ability to contract and release their “veins” to push their sap/blood around. It is slower than an animal’s circulation, but definitely a form of blood flow.

Many plants form non-succulent leaves that have a much more limited lifespan, and some small plants (like grass) do not make succulent tissue above ground. When temperatures drop below freezing, perennials dry out their soft tissue and go dormant. Think of what eastern prickly pears (opuntia humifusa) do to avoid frost.

There are evergreens, but they mostly exist in places that are nearly always below freezing. They still have soft tissue, but seem to have proteins that prevent tissue from freezing and sometimes produce heat.

Plants do produce fruit and get animals to distribute their seeds.

Mixotrophs

One of the two categories of “animals”, mixotrophs have a lot in common with “plants”, and are arguably just a subcategory that evolved a mobile life stage. They start their lifecycle as autotrophs (pretty much the same as plants, growing from seeds, rooting and accumulating mass and energy), but metamorphosis into a non-rooted mobile stage after accumulating enough energy and mass.

Most produce several clones at this stage, and the ones that fill the insect niche can produce thousands. They grow muscles (although mixotroph and osteoderm muscles are fundamentally different) and directing nervous systems and hunt for food to draw nutrients from (rather than having roots). They still get a lot of their chemical energy from photosynthesis.

They have the same fibrous bones (basically very dense flexible wood), fleshy tissue containing their circulatory system (although they have more organs) and translucent skin that “plants” have. Being mobile, they can typically spread their seeds pretty far. Mixotrophs primarily fill the ecological niches invertebrates (including insects), amphibians and reptiles do on Earth.

Fungi

Fungus is pretty similar to how it is on Earth, meaning very broad.

Osteoderms

Warmblooded heterotrophs, the osteoderms are the most directly analogous to “animals” from Earth. They primarily fill the ecological niches mammals and birds do on Earth. The keratin structures that make hair, claws, horns, est. never evolved, nor did live birth or multiple sexes.

Although many species have significant bone plating or other osseous structures outside of their bodies (weaponized things like antlers, for example), some have very minimal plating. Airborne species often have minimal plating, most only using them as nails.

Osteoderms rely mostly on body-fat, circulation and burning calories for heat to resist the cold. Lacking the insolation of fur, a lot of species are less cold resistant than cold-environment mixotrophs (since such mixotroph species have proteins to resist frostbite).

Note: Gosaa are a bit weird from a natural sciences perspective, and it is debated what other species they may be related to. The closest seems to be certain variants of fungus that fill the niche of algae, but only because the cells are very similar. They don’t really have any apparent relatives.