The types of animals found on worlds are defined through broad types. Exactly what they look like is left to the textual descriptions.
Many animals have “Large”, “Huge”, “Gigantic” variants. How big they are depend on the type of animal.
Any form of small animal, millimetres in size. They are mostly ignored once larger animals have evolved.
A mostly sessile type of organism which filters water through its body, and has few specialised body parts. They normally attach to the sea floor.
Amorphous, floaters/swimmers which often use venomous tendrils to catch prey. They evolve early on.
Marine creatures with a hard shell, either fixed to a surface or can crawl along the sea bed.
Things that crawl along the sea floor. Often invertebrates with hardened exoskeleton.
Things that swim in the sea, often vertebrates. Normally begin at around 10 centimetres in size, then going up to Large (metre), Huge (metres) and Gigantic (tens of metres) in size. Basically, fish.
Things that swim and have long muscular tentacles. Similar to squid and octopus.
Creatures that live on the shore line and share time between water and land, denoted by their ecology rather than by what they do. Will be notable early on, but fade into the background later.
Small animals that are normally scavengers, sometimes hunters. Make for poor quality meat.
Herbivores which spend most of their eating. Often herd animals. Generally used to produce meat.
Carnivores which hunt other animals. Often make for good live capture.