Invertebrates known to have the most complex brain belong to the octopus species. Brain composition is similar in some ways to that of humans in that they possess both long and short term memory. Their brain functions allow for easy problem solving and learning through trial and error and experience. Similar problems can be solved repeatedly once the initial problem has been solved.
Another sophisticated design similar to that of humans are the eyes. The lenses differ in that the shape changes in humans as opposed to moving in and out. The vast majority of octopuses, however, are colour-blind.
Octopuses are highly receptive to touch and most of their sensitivity is focused on the rim of the suckers. Chromatophores found on the skin allows for blending into its natural environment when alarmed. The colour can also be dependent on its mood with white signalling fear and red for anger; the neutral colour being brown. The Giant Octopus (Enteroctopus) is the largest octopus inhabiting our oceans and is an example of a species known to exhibit this kind of colour changing behaviour.
Most octopus species are able to secrete a toxin which is used during feeding. The blue-ringed octopus (Hapalochlaena), however, are one of the few most deadly species known to mankind and can carry more than one kind of venom. These toxins are used for either feeding or self-defence. Although the beak is comparatively small, it also has the ability to tear through a scuba diver’s wetsuit. Large, blue rings cover the dorsal surface of their mantle and web and extend down their arms. The rings on the body give off a fluorescent blue colour when alarmed which therefore makes it very distinguishable from other species.
The Giant Octopus Enteroctopus
The largest species of all the Cephalopods inhabiting the world’s oceans are the Giant Pacific Octopus (Enteroctopus dolfeini). Enteroctopus has a fairly wide distribution with Enteroctopus magnificent found inhabiting the cold waters of South Africa. The depth at which these particular species are found range from the intertidal down to 750 m. Some species on which they feed include crustaceans, bivalves and sharks. Their unique feeding behaviour involves secretions from the salivary papilla which soften the exoskeleton of their prey allowing for easier access. A toxin is then released into the tiny hole made by the radula in order to paralyse their prey before consumption.
Enteroctopus magnificent are oviparous with internal fertilization taking place. The female lays between 20 000 and 100 000 eggs in a rocky den which she guards during the entire incubation period. Incubation varies between 5 – 7 months depending on the ambient temperature. The female does not consume any food during this period and dies shortly after the juveniles have hatched. The juveniles are about the size of a grain of rice and spend 1 – 3 months drifting with the phytoplankton on the surface of the ocean before settling on the bottom of the ocean floor.
Figure 1. Enteroctopus magnificent in Cape Town, South Africa
The Blue Ringed Octopus Hapalochlaena
The most deadly of all the Cephalopods are Hapalochlaena. The two most well-known species are the Lesser (Southern) blue ringed octopus H.maculosa and the Greater blue ringed octopus H. lunulata. The Lesser is larger in size and more common than the Greater.
The distribution of H. lunulata is shallow reefs and tidal pools from northern Australia to Japan, including Papua New Guinea, Solomon Islands, Philippines, Indonesia and as far west as Sri Lanka. The depth at which these species are found range from 0 – 20 m. Hapalochlaena maculosa can only be found in temperate waters of southern Australia, from southern Western Australia to Victoria. Hapalochlaena feed on small crabs and shrimp and hunting takes place during the daytime.
The female lays between 50 – 100 eggs which are carried in her tentacles until they are ready for hatching. The incubation period lasts for 50 days. The female does not eat during this period and eventually dies after the juveniles have hatched. The juveniles are about the size of a pea when hatched and grow to the size of a golf ball.
Being the biggest does not necessarily mean the most dangerous and in this case, size does not matter. Some animals have the potential to cause great harm and it is imperative to know which species are the most venomous to keep out of harms way.
Figure 2. Hapalochlaena maculosa in Ambon, Indonesia
The Coconut Octopus Amphicotus
Defence mechanisms vary among cephalopod species. The Coconut Octopus Amphicotus marginatus has an unusual ability to create a fortress around itself using coconut halves. This behaviour was first noted in the tropical waters of Indonesia where empty coconut shells were discarded. This beautiful octopus, distinguished by its bright blue suckers, is one of only two species that exhibit bipedal behaviour (the other one being Abdopus aculeatus). This movement is thought to mimic a floating coconut to protect itself from predators.
Figure 3. Amphicotus marginatus in Sulawesi, Indonesia