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Hermit octopus (Diogenopus vermisomus)

By AlexSone
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Order: Octopuses (Octopodida)
Family: Porter octopuses (Phoroctopidae)
Habitat: mollusk-spongial reeves of Pacific Ocean.

Octopuses are cephalopods completely lost their shell: even a rudiment of this structure is not remained at them. Therefore they can not rely upon passive protection as it was made by their relatives – ammonites and nautiloids. Feature of behavior of octopuses is their disposition to hide into different kinds of shelters. And absence of firm parts of body gives them big advantages in this sense: octopus can hide in very narrow shelter, where predator having a firm skeleton, will not squeeze through. But shelter is not always “near at hand”: the mollusk should leave it to hunt. In Neocene some octopuses have solved this problem by very simple way: they simply began carry shelter on themselves. The most simple and accessible among small and enough strong shelters on Neocene reeves are mollusk shells. During evolution process the special family of octopuses, which have mastered using these shells for daily life similarly to hermit crabs, has appeared.
The characteristic representative of this family is the hermit octopus. It is medium-sized mollusk: its tentacles are up to half meter long (measurements of the female are described here, male is much smaller). At usual octopuses leading free life there is short and thick body, but at this mollusk body is long and flexible. Hermit octopus practically constantly drags on itself found mollusk shells in which it hides in case of danger, therefore such body shape permits it to use volume of portable shelter most rationally. In connection with such unusual habit of life its tentacles have a little changed: from eight tentacles two ones (last pair) became short, flat and wide, and their bases have moved back and upwards. These tentacles are intended for keeping of shell on the body of mollusk, therefore getting it out from the shelter is rather uneasy: for keeping at smooth internal surface of shell on these tentacles suckers are well advanced. Other tentacles have a structure typical for octopuses, and are used the same way as usually. The hermit octopus has kept ability to change colouring of body, but its body nevertheless makes it less successfully, than head and tentacles. In rest colouring of tentacles is grey with pinkish and white “marble” pattern of cross strips and spots, but it also can change from white up to rubiginous and black color. Eyes are large, greenish with white rings around, exaggerating visually their size.
At all species of hermit octopuses both males and females search and carry shells.
This kind of octopuses is named after the philosopher of human epoch Diogenes, lived, as the legend says, in barrel. Such name rather precisely indicates features of behavior of this octopus: characteristic for these cephalopods aspiration to occupy various shelter has resulted to that hermit octopuses have originally returned to feature which their far ancestors have refused millions years ago. However, as against fossil cephalopods, carrying shell till all their life, the hermit octopus can leave it at the will not for a long time. It makes it very seldom, and only when there is no other way to reach any significant purpose. However it does not leave from the house far: by one tentacle the hermit octopus constantly keeps for shell, being ready at any moment to involve itself in shelter by sharp contraction of this tentacle.
Because of heavy shell and thin long body the hermit octopus has lost the ability to swim. Usually it creeps on the bottom, extending forward the forward pair of tentacles and tighten on them. It does not have need to swim quickly: its food in case of danger does not aspire to rescue by flight. Similarly to all cephalopod, this octopus is a predator. It eats crustaceans and fishes dug at danger in sand, or hiding in holes. Usually such octopuses one by one wander on reef, tracing for smells dissolving in water. Having felt smell of possible catch, octopus slowly moves to its source. It does not try to disappear: it has no need to creep as closer, as it is possible, and then to rush and to chase prey; it hunts by other way.
Having noticed a predator, any fishes and shrimps swim out, and any ones hide themselves in sand. This mollusk also hunts for them. It immerses tentacles in sand, and sensitive chemoreceptors on their surface permit this mollusk to define, where there is a catch. Though the mollusk does not see prey, it chases it in thickness of sand by tentacle by smell. If the catch dug in sand will try to slip away, electroreceptors catching activity of nervous system of hidden catch include to hunting. 
Strong suckers at tips of tentacles help to keep seized catch. When the chased animal has got, octopus jerky contracts tentacle and pulls catch out from sand. Even if at this moment it will escape, it will not be possible to rescue to it: octopus covers a place of hunting by shell in which it is sitting, and catch slipped away all the same appears in trap.
Octopus kills caught prey by sting which is very poisonous and instantly kills even animals with slow metabolism. With the help of stings octopus protects itself from enemies – predatory fishes and other species of octopuses. For protection another traditional for cephalopod kind of weapon, poisonous ink, is also used. But it is the extreme case: ink is poisonous for the octopus, and it can not leave quickly the poisoned zone. Therefore it splashes ink through swimming funnel extending like tube, and at once presses shell to bottom. If the bottom is sandy, octopus even “anchors”, deeply immersing free tentacles in sand and being dug in it by edges of shell.
For breeding male finds female by smell emitting by it. Having found shell of the female, male cautiously gets on it, and waits, while the female will find out his presence herself. If he will be careless, the female may easily have eaten him. When the male will be convinced, that the female knows about his presence, he cautiously starts closer acquaintance: he warns her about his intentions by easy touches to tentacles of the female. The female unready to pairing simply banishes the unlucky “groom” by impact of tentacle. If the female is ready to pairing, she lets tentacles out and touches by them the male, answering him. An accustoming of animals to each other proceeds so. For pairing the male pushes tentacle filled with sperm liquid (it is larger than others) in pallial cavity of the female, and then by sharp contraction of muscles in the basis of this tentacle tears it off. His mission in breeding is executed, and the male leaves out. The torn off tentacle will regenerate, and he one – two times again can repeat courtship. His tentacle some time lives in pallial cavity of the female. When she starts to lay eggs, this tentacle bursts and fertilizes them. 
The female of this species carries eggs pasted in vault of shell like grapes. As all octopuses, during protection of posterity she becomes inactive and eats of nothing. Development of eggs lasts about one month, and then from them tiny translucent youngs hatch. First some days of life they spend in shell near to mother. They hang on wall of shell almost motionlessly. At this time at them large yolk sac resolves, and body gradually starts to get colouring. After the young growth abandons shell, female lives not for long: about one week. In her organism irreversible physiological changes take place, and she perishes.
Leaving from parental shell, young hermit octopuses first two months live usual life, characteristic for the majority of octopuses. Later their body starts to extend, and they look for a shell to themselves.
Hermit octopuses are short-lived: duration of their life does not exceed three years.

Original drawing by Tim Morris.
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© 2017 - 2021 AlexSone
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Koba116's avatar

Do they exchange shells

Amplion's avatar
Ух ты какой! Вы с Тимом отлично постарались!
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ClassyBoogeyman's avatar
This looks really cool^^
ClassyBoogeyman's avatar
You are very welcome^^
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