You are browsing the archive for 2012 October.

Blue ringed octopus

October 28, 2012 in Articles 2012-13

The blue ringed octopus though incredibly small are the most deadly of the cephalopods due to their highly toxic venom. There are multiple species of the blue ringed octopus. One of the most common is the lesser blue ringed octopus (Hapalochlaena maculosa). The lesser blue ringed octopus has a body up to 5cm long and arms up to 10cm long. The lesser blue ringed octopus’ name is derived from the size of the blue rings it creates when it is threatened. The size of the rings will generally be less than 2mm in diameter. The dorsal surface of the lesser blue ringed octopus has a rough appearance due to the irregularly arranged wrinkles. When the octopus is not under threat its colouration is beige with large light brown patches known as maculae. When the octopus is agitated these brown patches will darken dramatically and bright blue rings will appear within them and may even pulsate. There will typically be 50-60 blue rings covering the lateral and dorsal surfaces of the mantle.

Blue ringed octopus when threatened (http://blogington.com/6-most-poisonous-animals-in-the-world/)

Hapalochlaena maculosa can be found only in the temperate waters of southern Australia. They live in waters up to 50m deep. Another species of blue ringed octopus, the greater blue ringed octopus (Hapalochlaena lunulata) can be found in shallow reefs or tide pools from the northern regions of Australia to Japan and has even been found as far west as Sri Lanka. It can be found at depths between 0-20m.

Mating in the blue ringed octopus.

The mating ritual for the lesser blue ringed octopus will begin when a male octopus approaches a female and then proceeds to caress her with his hectocotylus. The hectocotylus is a specially adapted arm. Once the male has finished caressing the female he will climb onto the back of her mantle. The hectocotylus is then inserted under the female’s mantle where the male will then release his spermatophores into the oviduct of the female. The male will die shortly after he has finished mating. The female will lay 50-100 eggs and will guard them by carrying them beneath her tentacles. This prevents the female from eating and so she will die shortly after the eggs have hatched. The eggs will usually take 50 days to hatch. When the eggs hatch the hatchlings will be about the size of a pea and will mature into an adult which is about the size of a golf ball. The hatchlings will mature very rapidly being able to mate the next year. Octopuses like squid and cuttlefish have a short life span of about 2 years. A study showed that male greater blue ringed octopus (Hapalochlaena lunulata) were not able to distinguish between males and females of the same species without the insertion of the hectocotylus under the mantle. The study recorded physical contact between pairs of octopus and copulation and also whether spermatophores were released. In the case of the male-male interactions 80% of the pairs made physical contact then proceeded to copulate. None of the male-male interactions had any spermatophores release recorded and the mounting male always removed his hectocotylus from the mantle of the other octopus and then dismounted. None of the male-male pairs were observed to show any aggressive behaviour to the other male before or after copulation.

Cross section of lesser blue ringed octopus showing concentrations of tetrodotoxin throughout the body.

Both the lesser and greater blue ringed octopus feed on small crabs and shrimp. The blue ringed octopus hunts during the day and uses the tetrodotoxin in its body to kill its prey. The method which the octopus uses to deliver the toxin is not known the octopus either bites its prey with its beak delivering the toxin in the saliva on the beak or the toxin is released into the water surrounding the prey in the octopus’s saliva. The tetrodotoxin in the blue ringed octopus is created by bacterium. Tetrodotoxin has been found to be present throughout the octopus’s body with the highest concentration in the arms.

The Mimic Octopus

October 22, 2012 in Articles 2012-13

Like many cephalopods, the mimic octopus (Thaumoctopus mimicus) has the ability to change the colour of its skin. However this species goes a step further and, as its name suggests, is able to accurately imitate up to 13 other animals present in its habitat. It typically has cream or white and dark brown bands and grows to have a maximum arm span of 60cm. It was discovered in the Indo-Pacific Ocean in 1998 and over the last few years has become known as a remarkable artist of disguise.

The mimic octopus is a sand and silt dwelling cephalopod that is found at depths of between 2 and 12 meters, close to river mouths in a habitat where the seabed is rich in fauna such as crustaceans and worms, which the octopus feeds upon. It is able to quickly alter its appearance and behaviour to camouflage itself, or scare potential predators by seemingly imitating potentially dangerous or venomous creatures. For example, to avoid attack from a territorial fish such as a damselfish, the octopus appears to mimic a banded sea snake which is poisonous and preys on small fish, like the damselfish. To achieve this, the octopus hides 6 of its arms behind its body in a hole and raises the remaining two arms in opposite directions, moving them in an undulating, curling fashion to imitate the movements of a snake. The intelligence of the mimic octopus is demonstrated by its remarkable ability to choose the species it mimics depending on the type of predator that it is threatening it.

Fig 1: Image showing the mimic octopus’s (Thaumoctopus mimicus) mimicry of the flatfish, lionfish and sea snake next to the corresponding animals

It is active during the daylight hours, which is fine for relatively stationary activities such as foraging as it can alter its skin colour and camouflage itself, however it poses the problem of moving between sites where it wishes to forage for food while maintaining camouflage to protect itself from predators. A solution to this is achieved by appearing to adopt the colouring, shape and style of movement of a common flatfish. The octopus has been seen on several occasions swimming between foraging sites such as worm holes in this way. To achieve this, the mimic octopus takes on the streamlined, leaf-like shape of the flatfish by trailing all its arms behind itself and by taking on the colouring of a specific species of sole that is found in the same habitat as the mimic octopus. This particular sole (Zebrias spp.) is very well camouflaged and moves quickly, undulating and hugging the sea bed. It also possesses two poison glands, thus making it unattractive to predators.

The mimic octopus’s apparent imitation of the lion fish is another example of its ability to take on the appearance of other organisms in order to move safely though open water as, due to its poison, most predators do not attack the lionfish. Although it is a predominantly benthic organism that lives and feeds on the sea bed, the mimic octopus is able to swim along a little above the sea –floor with its arms matching the colouring of the lionfish and trailing behind it, like the lionfish’s poison tipped spines.

It is specialised cells in the skin of the octopus that reflect, absorb, diffract and scatter light in different ways and so create the colour changing ability of the mimic octopus which makes the majority of the different appearances it is able to assume possible. There are 4 different types of cell that facilitate colour change, the main type being chromatophores.

Chromatophores are found directly under the surface of the skin of cephalopods. These are groups of cells that include a pigment contained in a saccule and a group of muscles that, when they contract, expand the saccule and make more of the pigment visible. The pigment contained in the saccule can be yellow, orange, red, brown or black in colour. Each chromatophore is attached to a nerve ending so when a trigger is sent from the brain the amount of visible pigment can be altered very rapidly across many chromatophores and a pattern produced.

Although chromatophores are the main colour change organs, the other colour changing cells types that are important too. A layer of skin below the chromatophores are the iridophores. These create the more metallic looking colours such as gold, green, blue and occasionally silver. These are not as easy to control as the chromatophores as they are not neurally controlled, but controlled by hormones. Another type of cells causing colouring in cephlopods are the leucophores that reflect and scatter light, meaning that they appear to be different colours depending on the predominant wavelength of the light of the area.

There is still much to discover about the mimic octopus as it is relatively new to science and, despite the popularity of this creature, there has been little research into it. This means that there is still a long way to go before we fully understand its intelligence and hopefully in the future we will be able to find out more about this amazing and bizarre creature.

 

 

References

Dynamic mimicry in an Indo-Malayan octopus, 2005, MARK D. NORMAN, JULIAN FINN AND TOM TREGENZA

Chromatophore Organs, Reflector Cells, Iridocytes and

Leucophores in Cephalopods, 1983, RICHARD A. CLONEY AND STEVEN L. BROCCO

Mimicry and foraging behaviour of two tropical sand-flat octopus species off North Sulawesi, Indonesia, 2008, ROGER T. HANLON, LOU-ANNE CONROY and JOHN W. FORSYTHE

The evolution of conspicuous facultative mimicry in octopuses: an example of secondary adaptation?, 2010, CHRISTINE L. HUFFARD, NORAH SAARMAN, HEALY HAMILTON and W. BRIAN SIMISON

http://www.thecephalopodpage.org/cephschool/howcephalopodschangecolor.pdf

 

Photo Reference

http://conservationreport.files.wordpress.com/2008/11/mimic-octopus.jpg