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Order Octopoda<< Cephalopod Species
Members of the order octopoda have eight arms. In cephalopods, the evolutionary trend has been a reduction in shell size. Octopuses, which have no shell at all, have carried this the furthest (Barnes 1987).
Suborder CirrataThese funky looking octopods have a pair of fins on their mantle, large webs, and cirri (small projections) on their arms. Most species are found in the deep sea.
Suborder IncirrataThe suborder Incirrata contains the more familiar unfinned octopuses.
Octopuses have evolved mechanisms to protect themselves from predators. Some of the remarkable abilities of octopuses include their ability to change their color, texture, and apparent size; to expel ink; and to modify their environment to suit themselves. Octopuses are able to jet water through their siphon by contracting their mantel to provide quick thrust. They have the intelligence and ability to get into and out of fishermen's crab and fish traps and to get under an under gravel filter plate in anaquarium (see Wood 1994). They can adapt to new situations and appear to be curious about their surroundings. Octopuses can use their bodies as a nets to trap fish. Having very little hard material in their bodies, usually only a beak and a radula, they can squeeze into amazingly small spaces.
The lack of a hard defensive shell seems to make the octopus an easy meal. However, the above adaptations are often used together to effectively evade predators. An octopus could darken in color, expel a cloud or decoy of dark ink, immediately jet away while turning white, and then disappear under a rock, leaving the predator confused.
Although octopuses possess beaks and cephalotoxins, they generally do not effect man. The exception is the beautiful blue-ringed octopus from Australia. While it is shy and definitely won't viciously 'attack', it can, if it feels threatened, defend itself and deliver a venom that can kill in minutes (Kerstitch 1990).
The life span of octopuses is short, varying from six months in small species to three years in larger ones (Boyle 1987). In laboratory studies of Octopus briareus, life spans ranged from ten to seventeen months. Boyle (1983) states that 'In the vast majority of natural deaths in the laboratory, both males and females have undergone a 2 to 4 week period of deterioration during which feeding was sporadic and the skin, arms and internal organs degenerated.' Boyle (1983) goes on to say, 'In most males, this deterioration occurred at varying periods after mating and growth to a larger size, and in females it occurred after egg laying and brooding.' It is believed that the hormone that regulates sexual maturation is also associated with natural death (Boyle 1983).
Another engaging aspect of octopuses is their reproduction. Boyle (1987) notes that 'It is generally thought that cephalopods are fast growing animals that reproduce once and then die.' In Octopus briareus, an impregnated female can store viable spermatophore for as long as one hundred days after fertilization (Boyle 1983). The eggs are generally laid in a protected lair and fanatically guarded by the female. She usually eats very little or not at all during this period and dies shortly after the eggs hatch. I have observed that even unfertilized females lay eggs, brood, and then die.
ReferencesBarnes, R.T. 1987. Invertebrate Zoology, 5th ed. Saunders College Publishing, Fort Worth. 893pp.
Boyle, P.R. 1983. Cephalopod Life Cycles. Vol 1. Academic Press, London. 475pp.
Boyle, P.R. 1987. Cephalopod Life Cycles. Vol 2. Academic Press, London. 441pp.
Kerstitch, A. 1990. Molluscan Touch. Seascope. Vol 7.
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The Cephalopod Page (TCP), © Copyright 1995-2016, was created and is maintained by Dr. James B. Wood, Associate Director of the Waikiki Aquarium which is part of the University of Hawaii. Please see the FAQs page for cephalopod questions, Marine Invertebrates of Bermuda for information on other invertebrates, and MarineBio.org and the Census of Marine Life for general information on marine biology.