Overview

Brief Summary

Introduction

The Cephalopoda is an ancient and very successful group of the Mollusca. Cephalopods have been among the dominant large predators in the ocean at various times in geological history. Two groups of cephalopods exist today: The Nautiloidea with a few species of the pearly nautilus, and the Coleoidea, containing the squids, cuttlefishes, octopods and vampire squids, which is represented by about 700 species. Cephalopods are the most active of the molluscs and some squids rival fishes in their swimming speed. Although there are relatively few species of living cephalopods, they occupy a great variety of habitats in all of the world's oceans. Individual species are often very abundant and provide major targets for marine fisheries.

Cephalopods first appeared about 500 million years ago in the Upper Cambrian Period. Although considerable uncertainity still exists, the two extant lineages may have separated 470 mya with the possible origin of the Bactritida or earlier. The long separation of the two lineages has, today, resulted in lineages with cephalopods that are very different in structure.

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Comprehensive Description

Classification

Much of the higher classification of Recent cephalopods is unstable. Various authors have suggested highly varying arrangements. We adopt a conservative arrangement that does not differ much from that of Naef (1921-23). Except for the position of the Octopodiformes and its two orders, we have a questionable phylogenetic basis for accepting this or any other scheme. We suggest, however, for the sake of stability, that the following classification be used until this or an alternative arrangement can be derived from cladistic analyses. The analyses, whether molecular or morphological, however, must be robust and must survive considerable scrutiny before changes in classification should be adopted.

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Characteristics

  1. A funnel derived from the molluscan foot (ref.?) or the molluscan neck region (Shigeno et al., 2007).
  2. Circumoral arms that are derived from the molluscan head (J.Z. Young, 1965) or the molluscan foot (Shigeno et al., 2007).
  3. Chitinous beaks.  

    Figure. Oral view of the buccal mass of the giant squid Architeuthis sp. The dark, chitinous, bird-like beaks are visible on the surface of the white muscle mass. Photograph by Mark Norman.

  4. Shell.
    1. Shell with a phragmocone and siphuncle.

      Figure. A longitudinal cut through the shell of the pearly nautilus (Nautilus sp.)showing the flotation chambers (phragmocone) and the siphuncle (partially lost from the larger chambers) that passes through the septa separating individual chambers. The shell has become internal and highly modified in most living cephalopods. Photograph by R. Young.

  5. Image-forming eyes.

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Physical Description

Morphology

Sexual Dimorphism

Sexual Dimorphism often pronounced in size, morphology and life history: reproductive organs of males (e.g. hectocotyl arm in octopods and squid) swollen and obvious when in reproductive condition; dwarf males common in parasitic forms and in pelgic octopods and squid; males may mature before females and have shorter lifespans.
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Ecology

Associations

Known predators

Cephalopoda (lobsters) is prey of:
Odontoceti
Spheniscidae
Phocidae
Cetacea
Aves
Actinopterygii
Hydrurga leptonyx
Mirounga leonina
Physeter catodon
Sebastes miniatus
Scorpaena guttata
Zalophus californianus
Scorpaenichthys marmoratus
Thunninae
Alepisaurus
Istiophoridae
Chondrichthyes
Merluccius
Cephalopoda
Scombridae
Thyrsites atun
Argyrosomus hololepoditus
Seriola
Atractoscion aequidens
Carangidae
phytoplankton
Epinephelinae
Cheloniidae
Decapoda
Stomatopoda
Anomura
Gastropoda

Based on studies in:
Antarctic (Estuarine)
Southern Ocean (Marine, Tropical)
South Africa, Southwest coast (Marine)
Puerto Rico, Puerto Rico-Virgin Islands shelf (Reef)
USA: California, Southern California (Marine, Sublittoral)
unknown (epipelagic zone, Tropical)

This list may not be complete but is based on published studies.
  • G. A. Knox, Antarctic marine ecosystems. In: Antarctic Ecology, M. W. Holdgate, Ed. (Academic Press, New York, 1970) 1:69-96, from p. 87.
  • B. C. Patten and J. T. Finn, Systems approach to continental shelf ecosystems. In: Theoretical Systems Ecology, E. Halfon, Ed. (Academic Press, New York, 1979) pp. 183-212 from p. 202.
  • T. A. Clark, A. O. Flechsig, R. W. Grigg, Ecological studies during Project Sealab II, Science 157(3795):1381-1389, from p. 1384 (1967).
  • N. V. Parin, Ichthyofauna of the Epipelagic Zone (Israel Program for Scientific Translations, Jerusalem, 1970; U.S. Department of Commerce Clearinghouse for Federal Scientific and Technical Information, Springfield, VA 22151), from p. 154.
  • N. A. Mackintosh, A survey of antarctic biology up to 1945. In: Biologie antarctique, R. Carrick, M. Holdgate, J. Prevost, Eds. (Hermann, Paris, 1964), pp. 3-38.
  • Opitz S (1996) Trophic interactions in Caribbean coral reefs. ICLARM Tech Rep 43, Manila, Philippines
  • Yodzis P (2000) Diffuse effects in food webs. Ecology 81:261–266
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Known prey organisms

Cephalopoda (lobsters) preys on:
phytoplankton filter feeders
Euphausia superba
Euphausia crystallorophias
predatory planktonic invertebrates
zooplankton
Actinopterygii
herbivorous plankton
plankton
Engraulis mordax
Exocoetidae
Diaphus splendidus
benthic carnivores
macrozooplankton
Engraulidae
Clupeidae
Etrumeus teres
Gonostomatidae
Callogobius atratus
Trachurus
Merluccius
Cephalopoda
Hemiramphidae
Decapoda
Stomatopoda
Anomura
Gastropoda
Priapula
Polychaeta
Ophiuroidea
Bivalvia

Based on studies in:
Antarctic (Estuarine)
Southern Ocean (Marine, Tropical)
USA: California, Southern California (Marine, Sublittoral)
Puerto Rico, Puerto Rico-Virgin Islands shelf (Reef)
unknown (epipelagic zone, Tropical)
South Africa, Southwest coast (Marine)

This list may not be complete but is based on published studies.
  • G. A. Knox, Antarctic marine ecosystems. In: Antarctic Ecology, M. W. Holdgate, Ed. (Academic Press, New York, 1970) 1:69-96, from p. 87.
  • B. C. Patten and J. T. Finn, Systems approach to continental shelf ecosystems. In: Theoretical Systems Ecology, E. Halfon, Ed. (Academic Press, New York, 1979) pp. 183-212 from p. 202.
  • T. A. Clark, A. O. Flechsig, R. W. Grigg, Ecological studies during Project Sealab II, Science 157(3795):1381-1389, from p. 1384 (1967).
  • N. V. Parin, Ichthyofauna of the Epipelagic Zone (Israel Program for Scientific Translations, Jerusalem, 1970; U.S. Department of Commerce Clearinghouse for Federal Scientific and Technical Information, Springfield, VA 22151), from p. 154.
  • N. A. Mackintosh, A survey of antarctic biology up to 1945. In: Biologie antarctique, R. Carrick, M. Holdgate, J. Prevost, Eds. (Hermann, Paris, 1964), pp. 3-38.
  • Opitz S (1996) Trophic interactions in Caribbean coral reefs. ICLARM Tech Rep 43, Manila, Philippines
  • Yodzis P (2000) Diffuse effects in food webs. Ecology 81:261–266
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Evolution and Systematics

Functional Adaptations

Functional adaptation

Suckers allow fine attachment: octopus
 

Suckers of the octopus hold objects smaller than the suckers by having tiny projections called denticles, 3-micrometer-diameter pegs.

   
  "William Kier of the University of North Carolina is studying the rows of muscular suckers along the arms and tentacles of octopi. Octopus suckers' tiny projections called denticles are 3-micrometer-diameter pegs that provide more intimate contact with the surface underneath. The denticles allow the suckers to grip a range of objects, including objects smaller than the suckers. This could be useful information for creating stronger human-made suction cups." (Courtesy of the Biomimicry Guild)
  Learn more about this functional adaptation.
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Functional adaptation

Arterial walls resist stretch disproportionately: cephalopods
 

The arterial walls of cephalopods and arthropods resist stretch disproportionately as stretch increases due to tissue architecture.

     
  "In effect, Laplace's law rules out the use of ordinary elastic materials for arterial walls, requiring that an appropriate material fight back against stretch, not in direct proportion to how much it's stretched, but disproportionately as stretch increases. Which, again in obedience to the dictates of the real world, our arterial walls do--aneurysms, fortunately, remain rare and pathological. We accomplish the trick first, by incorporating fibers of a non-stretchy material, collagen, in those walls, and second, by arranging those fibers in a particular way. Thus, as the wall expands outward, more and more of these inextensible fibers are stretched out to their full lengths and add their resistance to stretch to that of the wall as a whole…Arterial walls that resist stretch disproportionately as they extend characterize circulatory systems that have evolved within lineages quite distinct from our own--in cephalopods and arthropods, for instance. Recruitable collagen fibers don't represent the only possible solution to the basic problem, and they're not nature's inevitable choice." (Vogel 2003:7-8)

"The most important mechanical property of the artery wall is its non-linear elasticity. Over the last century, this has been well-documented in vessels in many animals, from humans to lobsters. Arteries must be distensible to provide capacitance and pulse-smoothing in the circulation, but they must also be stable to inflation over a range of pressure. These mechanical requirements are met by strain-dependent increases in the elastic modulus of the vascular wall, manifest by a J-shaped stress–strain curve, as typically exhibited by other soft biological tissues. All vertebrates and invertebrates with closed circulatory systems have arteries with this non-linear behaviour, but specific tissue properties vary to give correct function for the physiological pressure range of each species. In all cases, the non-linear elasticity is a product of the parallel arrangement of rubbery and stiff connective tissue elements in the artery wall, and differences in composition and tissue architecture can account for the observed variations in mechanical properties. This phenomenon is most pronounced in large whales, in which very high compliance in the aortic arch and exceptionally low compliance in the descending aorta occur, and is correlated with specific modifications in the arterial structure." (Shadwick 1999:3305)
  Learn more about this functional adaptation.
  • Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
  • Shadwick, R. E. 1999. Mechanical design in arteries. 3305-3313 p.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
Specimen Records: 5413
Specimens with Sequences: 5071
Specimens with Barcodes: 4825
Species: 432
Species With Barcodes: 401
Public Records: 3727
Public Species: 305
Public BINs: 398
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Barcode data

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