These animals need to have occasional access to saltwater. Active transport of water or salt. Fish can transport salt ions back into body thru gill, get it from food. Evolutinary history as freshwater spp. Reptiles, seabirds have salt glands to excrete salt actively.
Sharks conserve trimethylamine oxide and urea in blood.
Form metabolic water by food oxidation esp. Must be reused to build proteins or be eliminated. Aquatic animals- Fish can excrete toxic ammonia from gills since water washes it away 2. Terrestrial animals B. Types of excretory organs 1. Fluid enters closed tube by pinocytosis, moves down tubes and is excreted thru skin pores.