Order: Octopuses (Octopoda)
Family: True octopuses (Octopodidae)
Habitat: Sea of Okhotsk, fields of floating algae.
Among the predators of the algal fields of the Sea of Okhotsk, cephalopods occupy an important place. These inhabitants of the sea bottom had found far from the coasts an environment completely suitable for life and representing interwoven brown algae, where it is easy to find shelter from the enemies and suitable prey like numerous small animals settling among the algae. The only limitation for cephalopods at the settling at the algal congestions is connected to the body size: the coastal giants cannot live among the algae. However the small octopi, populating the algal fields of Sea of Okhotsk, are very diverse. The absence of hard skeleton makes possible for them to squeeze into the narrowest slots, and in the thick interlacements of algae they feel themselves like a duck to water, creeping among the algae with the aid of their tentacles.
One of the small octopi populating the algal fields of Sea of Okhotsk is the monkey octopus, a mollusc having body length of about 6 cm. The body of monkey octopus is flattened into an oblate shape. The tentacles are about 20 cm long, wide and flattened, ribbon-like with rounded tips. Their suckers are arranged in two rows. At this octopus the suckers have significant mobility and they can make “steps” like movements of the caterpillars. With the aid of the suckers’ movements monkey octopus can slowly creep up to its prey, without giving itself away by superfluous motions. When the monkey octopus does not hunt, it moves among the algae, grasping them by its tentacles as monkey does with its paws. The adult mollusc of this specie has lost the ability to swim – being out of the algae thickets monkey octopus feels itself very insecure. Having found itself in open water, this mollusc attempts to keep itself afloat, waving its tentacles. Simultaneously it stretches out its tentacles in the direction of the nearest strands of algae, attempting to find support. The funnel of this mollusc is underdeveloped, and the mantle cavity is considerably smaller than of the octopi leading a mobile way of life and able to swim.
Skin respiration plays an essential role in the respiratory metabolism of monkey octopus. At the upper side and along the sides body of this mollusc is covered with the leaf-like outgrowths, which simultaneously perform the function of “additional gills” and provide camouflage. When resting, the octopus stretches them out, increasing the surface of its skin, but in case of danger they contract strongly and take the shape of small tubercles on the mollusc’s skin.
The body of monkey octopus is coloured in brown with greenish specks and orange spots above the eyes and along the sides of body. The lower side of the tentacles is white. Depending on its emotional and physical condition, this mollusc can change colour from white to dark red, orange, green or brown with various switches between aforementioned colors and their combinations. The eyes of this mollusc are large and mobile, can rise above the body. Above each eye there are several branching outgrowths of skin that disguise the eye. The sight of monkey octopus has an important special feature – it notes the slightest motion in the motionless environment. It helps the octopus to find prey among the algae, where visibility is very poor. Also the monkey octopus has very keen sense of smell. The bite of monkey octopus is poisonous for the crustaceans and fishes – the mollusc feeds on them predominantly.
This mollusc breeds once a life. The male avoids direct encounters with the female – at this species cannibalism is very common, and the male (it is smaller, than female) has a chance to fall prey of the female. Having found a female, the male approaches it from a safe distance and with the sharp reduction of muscles breaks off one of its tentacles – the hectocotylus, filled with sperm. This tentacle finds the female by itself via smell and creeps into her mantle cavity, where the fertilization of eggs takes place. After the detaching of hectocotylus male remains alive. It grows new hectocotylus and can fertilize the next female. At this time the male does not eat, and perishes after the loss of second hectocotylus.
The clutch of this species amounts 40 – 50 thousand of small eggs; female bears them on the front pair of tentacles. When bearing the clutch, the female builds for itself a kind of a nest, bending the strands of algae to speric construction, in middle of which it hides, keeping the “walls” of its shelter by tentacles. The incubation lasts for three months, and all this time the female eats of nothing. After the hatching of larvae it dies soon.
The young monkey octopi can swim and settle to great distances before they grow up and pass to settled way of life. The sexual maturity of this species begins at the third year of life.
Original drawing by Tim Morris