Nocturnal Species


Feb 19, 2005
Hello all,

After two weeks and a neat little pile of hermit shells and crab husks, i was getting frustrated that i wasn't seeing my little occy hunting during the daylight hours. So after taking some advice from other Tonmo members i installed a red flourescent light, which i switch on when i arrive home at 6pm, hoping that this would bring out the little guy. I didn't see anything for two nights - then without warning, as i was just about to hit the sack, bout 10pm, he emerged from nowhere and put on an amazing display (my whole family was crowded around the tank for a good 2 hours). He moved around like he owned the joint, playing with empty shells, changing colour and trying the catch the boxer shrimp. he seemed fascinated by his reflection as he would move slowly laterally along the glass and curl his front tentacles. He has done this for the last 2 nights, emerges around the same time and is gone in the morning.

Anyway my question is this - Does this very confident behaviour during the night and absence during the day necessarily indicate a nocturnal species or could he just be wary of daylight predators as a youth(he is quite small head about the size of a marble, 3 cm tentacles)? Does anyone know of nocturnal species that have become day active after a long period of time in the tank?

thanks alot

Most octopus species are nocturnal (or live very deep). Diurnal or crepuscular species are the exception. The behavior that you describe is typical of a nocturnal species such as O. mercatoris or O. bocki.

"Pacing" along the side of the aquarium is also typical. It really doens't have anything to do with seeing a reflection - it is more a lack of understanding about glass.

And if I could offer one correction, octopus have arms, not tentacles.
Neogonodactylus said:
And if I could offer one correction, octopus have arms, not tentacles.

While you're on the subject, I've never really been clear on the difference. Could you provide definitions in this context?

Arms are appendages with suckers along their entire length. Tentacles are generally smooth-stalked (though they may have variations on the 'locking-apparatus' theme, i.e. alternating suckers and bumps along the oral face that 'zip' together and should enable the tentacles to support each other somewhat), with a club at the end - a pad (usually expanded or wider than the stalk) of specialized armature that ranges from a variety of suckers to sessile and swivelling hooks.
Octopus have arms only; most squid (and cuttlefish) have eight arms and two tentacles, although some species lose the tentacles at very early stages.
Hope this helps. :smile:

Incidentally, the Tree of Life Cephalopoda Glossary has lots of good explanations of terminology, and has this to say about tentacles:

'Tentacles - Modified 4th pair of appendages in decapodiforms that are capable of considerable extension and contraction. Although the tentacles are derived evolutionarily from the 4th pair of arms, the term, "arms IV" is reserved for the subsequent arm pair, the ventral arms, which are evolutionarily the 5th pair of arms. Each tentacle consist of a proximal stalk usually devoid of suckers, and a distal club armed with suckers and occasionally hooks.'

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