This Pacific red octopus (Octopus rubescens) is using water jet propulsion, which allows the animal to move in any direction and also alter its course quickly. The process is the same whether the animal is simply breathing or moving through the water. For jet propulsion to occur, water flows into the mantle cavity and over the gills. The mantle builds internal pressure by sealing off all openings, except a tube called the funnel or siphon. The thick muscles of the mantle wall contract, squeezing water out of the narrow funnel with enough force to propel the animal with a burst of speed. The Pacific red octopus can have an arm span up to 20 inches (50 cm) and weigh in at around a pound (0.4 kg), with a range from central Alaska to northern Mexico.