has 8 arms (not tentacles) with suckers in the form of concave dots on the arms which are used to move on the seabed and catch prey. The octopus arm is a structure muscular hydrostat which consists almost entirely of layers of muscle without bones or exoskeleton . Unlike other cephalopods, most of the octopuses of the Incirrata suborder have a body made up of muscles and no internal skeleton. Octopuses don't have an outer shell as a protector like the Nautilus and don't have an inner shell or bones like cuttlefish and squid. The beak is the hardest part of the octopus's body which is used as a jaw to kill prey and bite it into small pieces.
This highly flexible body allows the octopus to squeeze itself into very narrow rocky crevices on the ocean floor, especially when escaping from predatory fish such as the sea moray eel. Lesser-known octopuses from the Cirrata suborder have two fins and an inner shell, which reduces their ability to squeeze into tight spaces.
Octopuses have a relatively short life span and some species only live for 6 months. Larger species such as the North Pacific giant octopus which can weigh up to 40 kilograms can live up to 5 years under the right environmental conditions. Reproduction is one of the causes of death, male octopuses can only live a few months after mating and female octopuses die shortly after laying eggs. Death is caused by the octopus neglecting to eat for about a month while guarding the unhatched eggs.
The covering of the abdominal part of the octopus body is called the mantle which is made of muscle and looks like a pouch. Octopuses have three hearts which consist of two hearts to pump blood to the two gills and a heart to pump blood to all parts of the body. Octopus blood contains protein Hemocyanin which is rich in copper to transport oxygen. Compared to Hemoglobin which is rich in iron, Hemocyanin is less efficient in transporting oxygen. Hemocyanin dissolves in plasma and is not bound by red blood cells so octopus blood is pale blue in color. Octopuses breathe by sucking water into the mantle cavity through both gills and exhaled through the siphon tube. Octopuses have gills with very fine divisions, originating from the growth of the outer or inner body which undergoes vascularization
