Monday, November 1, 2010

The Cephalopoda aka octopus

The Cephalopoda

Polypus levis Hoyle (male) - Port Gazelle, Keguelen
Polypus levis Hoyle (male) - Port Gazelle, Keguelen

Opisthoteuthis medusoides + extensa
Opisthoteuthis medusoides + extensa

"In 1898, the steamship Valdivia left Hamburg for a nine month scientific voyage to the Atlantic, Indian and Great Southern oceans [map]. Known as the German Deep-Sea Expedition, the mission was led by Leipzig University Professor of Zoology, Carl Chun and investigated chemical, zoological and physical characteristics encountered in the oceans during the voyage."

"Professor Chun contributed a book on cephalopods (with a corresponding illustration/photograph atlas) to a multi-volume work called 'Wissenschaftliche Ergebnisse der deutschen Tiefse eexpedition auf dem Dampfer Valdivia' (From the Depths of t
he World Sea: Descriptions of the German Deep Sea Expedition)."

From the intro to th BiliOdyssey blogspot.

Velodona togata (off Somalia)
Velodona togata (off Somalia)

The octopus (Greek Ὀκτάπους, 'eight-legs') is a cephalopod of the order Octopoda that inhabits many diverse regions of the ocean, especially coral reefs. The term may also refer to only those creatures in the genus Octopus. In the larger sense, there are 289 different octopus species, which is over one-third of the total number of known cephalopod species.

Octopuses are characterized by their eight arms (not tentacles), usually bearing suction cups. These arms are a type of muscular hydrostat. Unlike most other cephalopods, the majority of octopuses — those in the suborder most commonly known, Incirrina — have almost entirely soft bodies with no internal skeleton. They have neither a protective outer shell like the nautilus, nor any vestige of an internal shell or bones, like cuttlefish or squids. A beak, similar in shape to a parrot's beak, is the only hard part of their body. This enables them to squeeze through very narrow slits between underwater rocks, which is very helpful when they are fleeing from morays or other predatory fish. The octopuses in the l
ess familiar Cirrina suborder have two fins and an internal shell, generally lessening their ability to squeeze into small spaces.

Octopuses have a relatively short life span, and some species live for as little as six months. Larger species, such as the North Pacific Giant Octopus, may live for up to five years under suitable circumstances. However, reproduction is a cause of death: males can only live for a few months after mating, and females die shortly after their eggs hatch. They neglect to eat during the (roughly) one month period spent taking care of their unhatched eggs, but they don't die of starvation. Endocrine secretions from the two optic glands are the cause of genetically-programmed death (and if these glands are surgically removed, the octopus may live many months beyond reproduction, until she finally starves).


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