Maldive octopus
Cephalopods, from the Latin for "head-foot," are among the strangest creatures in the ocean. Though classified in phylum Mollusca, they seem vastly different from snails or clams. They are among the smartest and most functionally diverse animals on the planet: flexible, adaptable, and well-equipped for rapid motion, effective hunting, and quick camouflage.
Their numbers include the giant squid, cuttlefish, and the beautifully coiled shelled nautilus. Now that the first octopus genome has been sequenced, scientists are beginning to learn about the complex genetic information behind their capabilities.
Nature published the first genome of a cephalopod, the California two-spot octopus,
Octopus bimaculoides. It was a massive undertaking. The octopus genome is comparable to the human genome in size and complexity. In fact,
it has "a greater number of protein-coding genes — some 33,000, compared with fewer than 25,000 in
Homo sapiens," says Alison Abbott in the same issue of
Nature.
This excess results mostly from the expansion of a few specific gene families, Ragsdale says. One of the most remarkable gene groups is the protocadherins, which regulate the development of neurons and the short-range interactions between them. The octopus has 168 of these genes — more than twice as many as mammals. This resonates with the creature's unusually large brain and the organ's even-stranger anatomy. Of the octopus's half a billion neurons — six times the number in a mouse — two-thirds spill out from its head through its arms, without the involvement of long-range fibres such as those in vertebrate spinal cords. The independent computing power of the arms, which can execute cognitive tasks even when dismembered, have made octopuses an object of study for neurobiologists such as Hochner and for roboticists who are collaborating on the development of soft, flexible robots.
A gene family that is involved in development, the zinc-finger transcription factors, is also highly expanded in octopuses. At around 1,800 genes, it is the second-largest gene family to be discovered in an animal, after the elephant's 2,000 olfactory-receptor genes. [Emphasis added.]
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