A Web-based tutorial on the circulatory system by Dr. Kenneth Chan, Department of Anatomical Sciences, University of Queensland. Compare other systems and the anatomy features in fish, mammals and amphibians. The bluefin tuna is warm-blooded, though not an endotherm like mammals. Some scientists believe the tuna has an adaptation in one of its eye muscles that allows it to shunt warm blood to the brain. Find out at the New England Aquarium website.
People often confuse sea lions and harbor seals.
Despite their similar appearance, they are not closely related. Each evolved from different ancestors, but both are pinnipeds, a suborder of marine animals. Sea lions have external ears and more developed limbs. Harbor seals are true seals. Next time you visit a zoo, see if you can tell them apart.