A Comprehensive List of Everything of which You Should Be Afraid

@Natalia - Octopus comes from Greek, not Latin. The "us" to "i" conversion for plurals is Latin.

Essentially, it's not Octop+us (which would imply Octopi) but rather, Octo+pus (eight + feet). The plural of pus (Greek suffix) is podes. Thus: Octopodes. The same is true for platypus/platypodes.

But since we speak English, Octopuses is actually preferable. In fact, this conversion (us --> uses) is correct in English for words of both Greek and Latin origin (cactuses, syllabuses, calculuses, etc.) and if you use it in every case, you'll avoid common mistakes such as happens with Octopus.

@Natalia -- I looked it up on the OED about a year ago. Sindigo is right. 'Octopuses' is a valid plural form.

Natalia, octopus can be pluralised as: octopuses, octopi or even octopodes. Arguably, the latter is correct as octopus is a greek word and adding the latin -i seems incongruous.

I'm not gonna say anything about the author of this title, just this: its Octopi...

I would add that some human neurons are not in the brain either. In particular the lower motor neurons. The upper motor neurons originate in the sensory motor cortex of the brain. They course down the corticospinal tract - decussating at the medulla - and terminate in various parts of the spinal cord. If I remember correctly the arm UMNs terminate in the lower cervical spine (vertebrae C5-T1) of the spinal cord where they innervate Lower Motor Neurons (LMNs). It is these LMNs that actually articulate the limbs. So as in the octopus, our limb articulating neurons are not in our brains either. However the signal to articulate the limbs originates in the brain.

Intelligence is generally related to brain-body mass ratio. Bigger bodies require more neural mass to articulate them. An octopus has virtually no skeleton and it's limbs are muscular hydrostats - like the human tongue. The neural real estate needed to articulate a hydrostatic limb is quite a bit greater than that needed for a limb supported by bone. For example; the cortical homunculus depicts this fact in humans. The neural mass needed to support the tongue is close to the same amount needed to articulate the entire leg and foot.

Octopuses consist almost entirely of hydrostatic limbs and probably there are more sensory nerve fibres innervating the limbs as well. This means the octopus can have a disproportionate brain-body mass ratio compared to typical animals without being super intelligent in the sense of being able to write any Broadway musicals.