Free-floating fauna in the ocean were not as prolific during the Cambrian as they would be later. While micro-bial mats were no longer ubiquitous, most Cambrian animal life that didn’t swim lived on or near the sea floor.
Whereas the Ediacaran witnessed the rise of the life’s lasting biomechanisms, the Cambrian’s great creation was carnivory: animals were eating other animals with zest. This set the evolutionary clock racing, sparking an incredible burst of speciation. While the Ediacaran was of evolution within animals, the Cambrian was of interaction between animals.
Crustaceans became the dominant invertebrate during the Cambrian. They occupied the shallow waters near seashores, which flooded inland during the early Cambrian.
The animal cardiovascular system was well-developed by 520 BYA. The vascular system of some ancient arthropods was more complex than what is found in many modern crustaceans: with simplification came efficiency.