Overview

Brief Summary

Introduction

Comments on this page refer to living Octopoda. for comments on extinct Octopoda see: Teudopseina and Incirrata.

Octopods have rather short, compact bodies and only eight arms; no trace of the missing second arm pair remains even during embryonic development. Many species are benthic (bottom-living) and crawl over the ocean floor with the mouth facing the substratum. Others alternate between a benthic and a pelagic (free-swimming) habitat and some species are completely pelagic. The two suborders of Octopoda are very different in appearance but there is little doubt that it is a natural group as the monophyly of the Octopoda is supported by a large variety of characters. The Cirrata is a group of deep-sea octopods commonly known as the "finned octopods" due to their large, wing-like fins. The Incirrata contain the common (benthic), shallow-water octopods as well as many deep-sea benthic and pelagic species.

Brief diagnosis:

An octopodiform ...

  • with one arm pair, presumaably true arms II, absent.
  • with suckers on proximal halves of arms.

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Comprehensive Description

Characteristics

  1. Arms
    1. Suckers with cuticular lining.
    2. Sucker stalks are broad, muscular cylinders.

  2. Head
    1. Nuchal cartilage absent.
    2. Inferior frontal lobe system present; superior buccal and posterior buccal lobes fused; suprabrachial commissure separate from brain (absent in Japetella).

  3. Funnel
    1. Funnel valve absent.

  4. Viscera
    1. Visceropericardial coelom reduced.
    2. Oviducal glands act, in part, as spermathecae.
    3. Oviducts with oviducal glands subterminally located on oviducts.
    4. Photosensitive vesicles located on stellate ganglia.
    5. Dorsal mantle cavity present.

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Ecology

Associations

Known predators

Octopoda (octopuses) is prey of:
Homo sapiens

Based on studies in:
USA: Alaska, Aleutian Islands (Coastal)

This list may not be complete but is based on published studies.
  • C. A. Simenstad, J. A. Estes, K. W. Kenyon, Aleuts, sea otters, and alternate stable-state communities, Science 200:403-411, from p. 404 (1978).
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Known prey organisms

Octopoda (octopuses) preys on:
Decapoda

Based on studies in:
USA: Alaska, Aleutian Islands (Coastal)

This list may not be complete but is based on published studies.
  • C. A. Simenstad, J. A. Estes, K. W. Kenyon, Aleuts, sea otters, and alternate stable-state communities, Science 200:403-411, from p. 404 (1978).
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Evolution and Systematics

Evolution

Discussion of Phylogenetic Relationships

The monophyly of both suborders is well established. Young and Vecchione (1996) found two apomorphic character states that defined the monophyly of the Incirrata:

  • Presence of a cornea.
  • Hectocotylization of one of the third arms.

Another character can probably be added to the list of apomorphies although it hasn't been included in a cladistic study:

  • Chorion of egg drawn out into a stalk (Young, et al., 1999).

Young and Vecchione (1996) found three character states that defined the monophyly of the Cirrata:

  • Spermatophores as sperm packets without ejaculatory apparatus.
  • Presence of horizontal arm septa.
  • Buccal position of posterior salivary glands.

Voight (1997) also found morphological, cladistic support for the Cirrata and Incirrata but her study is controversial. Carlini (1998) found molecular analyses supported the monophyly of both groups.

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Functional Adaptations

Functional adaptation

Ink cloud distracts predators: octopus
 

The ink cloud emitted by an octopus when threatened aids escape because it resembles the shape of the octopus.

   
  "When their speed alone is not enough for safety, [cuttlefish] squirt a cloud of dense, dark coloured ink that is synthesised in their bodies. This ink surprises their predators for a few seconds, which is usually enough for them to escape." (Yahya 2002:104)

"Sometimes the ink cloud itself resembles the blobby shape of an octopus and acts as a decoy, allowing the octopus to escape while the predator eyes the blob." (Crump 2005:109)
  Learn more about this functional adaptation.
  • Crump, M. 2005. Headless Males Make Great Lovers & Other Unusual Natural Histories. Chicago, IL: University of Chicago Press. 199 p.
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Functional adaptation

Siphon directs underwater movement: octopus
 

Siphons of octopi, squid, and cuttlefish jet through the water with directional control via jet propulsion.

     
  "Octopuses, squid, and cuttlefish have a more sophisticated version of jet propulsion. They expel water through a moveable tube called a siphon, which combines power with directional control." (Downer 2002:17)
  Learn more about this functional adaptation.
  • Downer, J. 2002. Weird Nature: An Astonishing Exploration of Nature's Strangest Behavior. Ontario: Firefly Books.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:2,327Public Records:1,772
Specimens with Sequences:2,137Public Species:104
Specimens with Barcodes:2,093Public BINs:128
Species:180         
Species With Barcodes:164         
          
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Barcode data

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Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Octopoda

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