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KNOBBY ARGONAUT
Argonauta nodosa
© shigeru.harazaki

The knobby or knobbed argonau is a species of pelagic octopus. The female, produces a very characteristic paper-thin shell, which is covered in many small nodules on the ridges across the shell. These nodules are less obvious or absent in juvenile females, especially those under 5 cm in length. The argonaut’s shell is runs approximately 5.5 - 10 inches (150 mm - 250mm in length). Males rarely surpass 3/4” (2 cm) and only mate once in their short lifetime, whereas the females are capable of having offspring many times over the course of their lives. In addition, the females have been known since ancient times, while the males were only described in the late 19th century.

Unlike most octopuses, argonauts live close to the sea surface rather than on the seabed. Argonauta species are characterised by very large eyes and small distal webs. The mantle-funnel locking apparatus is a major diagnostic feature of this taxon. It consists of knob-like cartilages in the mantle and corresponding depressions in the funnel. Argonauta species lack water pores.

Argonauts use tentacles to grab prey and drag it toward the mouth. It then bites the prey to inject it with poison from the salivary gland. They feed on small crustaceans, mollusks, jellyfish and salps. If the prey has a shell, the argonaut uses its radula to drill into the organism, then inject the poison.

Argonauts are capable of altering their color, blending in with their surroundings to avoid predators. They also produce ink when the animal is being attacked. This ink paralyzes the olfaction of the attacker, providing time for the argonaut to escape. The female is also able to pull back the web covering of her shell, making a silvery flash, which may deter a predator from attacking.

Source: http://en.wikipedia.org/wiki/Argonaut_%28animal%29

Source: animalworld