Overview

Brief Summary

Introduction

We place three families in the sepioid clade: Sepiidae, Sepiadariidae and Sepiolidae. The latter two families are related and placed in the suborder Sepiolida. Two additional families (Idiosepiidae, Spirulidae) have often been included in the Order Sepioidea. However considerable uncertainty exists concerning the relationships of the Idiospiidae in general and the closeness of the relationship of the Spirulidae to the sepioid families. Members of the sepioidea are mostly neritic and upper slope benthic species although one group (Heteroteuthinae) is pelagic.

Brief diagnosis:

A decapodiform ...

  • with corneal membranes covering eye lenses.
  • without branchial canals in gills.
  • with circularis muscles in suckers.

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Comprehensive Description

Characteristics

  1. Arms
    1. Suckers with circularis muscles.

  2. Tentacles
    1. Tentacular club without proximal (= carpal) locking-apparatus.
    2. Suckers in more than four series (except in some Sepiolidae).
    3. Suckers with circularis muscles.

      Figure. Sections through the club suckers. Left - Sepia officinalis, arrow points to circularis muscle which encircles the sucker. Middle - Ommastrephes bartramii. Note absence of a circularis muscle. Right - Sepia officinalis, section at right angles to left figure, circularis muscle in blue; the asymmetry in the muscle is revealed by the angle of section. Histological sections made by Barbara Littman; photographed by R. Young. Drawing modified from Naef (1921-23).

  3. Buccal crown
    1. Buccal supports with or without suckers.

  4. Head
    1. Head with tentacle pocket.
    2. Eyes with corneal membranes covering lenses.
    3. Eyes with secondary (= ventral) eyelid (except in some Sepiolidae).

      Figure. Lateral view of head of Rossia sp., 19 mm ML, preserved, showing secondary eyelid covering the ventral region of the transparent cornea. Photograph by R. Young.

  5. Funnel
    1. Funnel with lateral adductor muscles (except in some Sepiolidae).

      Figure. Ventral view of mantle cavity of Semirossia tenera (Sepiolidae). Photograph by M. Vecchione.

  6. Mantle
    1. Mantle locking-apparatus does not reach anterior mantle margin (see short arrow in above photograph which marks the anterior end of the mantle locking-apparatus) except in some Sepiolidae.
    2. Interstellate connective absent (ie, no direct nerve connective passes directly from one stellate ganglion to the other).

  7. Fins
    1. Fins completely separate from one another; usually with posterior lobes.

  8. Shell
    1. Shell a flattened phragmocone (=cuttlebone), a gladius or absent.

  9. Viscera
    1. Gills without branchial canal.

      Figure. Diagramatic cross-section through gills. Drawing modified from Naef (1921-23).

    2. Right oviduct absent.
    3. Females with accessory nidamental glands.

  10. Eggs
    1. Eggs, where known, attached to substrate singly or in unorganized groups.

Synapomorphies

Many of the above characteristics of the Sepioidea are shared with the Myopsida. The characters that unite the Sepiidae and the Sepiolida and are considered to be apomorphic (newly derived) characters are (characters 3 and 5 seem to be independently derived in a few Myopsida):

  1. Eyes with secondary eyelids.
  2. Funnel with lateral adductor muscles.
  3. Mantle locking-apparatus that does not reach the mantle margin.
  4. Absence of an interstellate connective.
  5. Gills without a branchial canal

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Evolution and Systematics

Functional Adaptations

Functional adaptation

Gas-holding structure aids buoyancy: cuttlefish
 

The cuttlebone of cuttlefish aids in maintaining buoyancy by using its chambered structure to keep a gas mixture at a relatively constant pressure.

   
  "Cuttlefish (which look like bulgy squid) have a foamlike or corrugated cuttlebone containing a gas mixture at nearly constant pressure (fig. 5.1)." (Vogel 2003: 97)
  Learn more about this functional adaptation.
  • Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
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Functional adaptation

Rapid color change used for protection: cuttlefish
 

The skin of cuttlefish changes color rapidly, in order to evade predators, using elastic pigment sacs called chromatophores.

       
  "To survive this turn of events required a pretty clever solution, and cuttlefish rose to the challenge in ways we are only just beginning to discover. We have known for a long time that these creatures have the world's best camouflage skills, but it seems this is just one of their many talents. Research published in the last few months shows cuttlefish can do things that are way beyond most molluscs and only rarely seen in mammals: their response to an approaching predator is tailor-made for the carnivore in question, for example. Not only that, they have also developed a secret communications system that could be the marine equivalent of invisible ink. You can almost imagine them sniggering at our primitive interactions from behind their eight arms.

"That said, cuttlefish are not above acknowledging the presence of lesser species such as humans, as divers around the world will testify. When they come across cuttlefish, some divers offer a greeting, the two-fingered "peace" sign. In what is surely one of the few cross-species salutations in the natural world, the cuttlefish reciprocates by lifting two of its arms. This message of peace is actually quite the opposite - a startle response to what the cuttlefish perceives as a threat. Sticking two fingers up at divers or predators is a secondary level of defence which cuttlefish use on the rare occasions that their camouflage fails.

"Cuttlefish and their fellow cephalopods - octopuses and squid - are masters of disguise, able to turn from completely invisible to totally obvious, and back, in about 2 seconds. They can use this trick to blend seamlessly into any natural background and will have a good stab at artificial ones too. While the skills of octopus and squid are not to be sniffed at, the cuttlefish is the king of cephalopod camouflage, according to Roger Hanlon of the Woods Hole Marine Biological Laboratory in Massachusetts. The fact that it achieves its disappearing tricks with a rigid cuttlebone, which means it cannot contort its body like an octopus, only makes it more impressive.

"Cephalopods have such remarkable camouflage primarily because of their chromatophores - sacs of red, yellow or brown pigment in the skin made visible (or invisible) by muscles around their circumference. These muscles are under the direct control of neurons in the motor centres of the brain, which is why they can blend into the background so quickly. Another aid to camouflage is the changeable texture of cuttlefish skin, which contains papillae - bundles of muscles able to alter the surface of the animal from smooth to spiky. This comes in pretty useful if it needs to hide next to a barnacle-encrusted rock, for instance.

"The final part of the cuttlefish's camouflage portfolio comes from leucophores and iridophores, essentially reflecting plates that sit underneath the chromatophores. Leucophores reflect light across a wide range of wavelengths so can reflect whatever light is available at the time - white light in shallow waters and blue light at depth, for example. Iridophores combine platelets of a protein called reflectin with layers of cytoplasm to produce iridescent reflections rather like those of butterfly wings. Iridophores in other species, like some fish and reptiles, produce optical interference effects that shift the light towards blue and green wavelengths. Cuttlefish can turn these reflectors on or off in seconds to minutes, controlling the spacing of the platelets to select the colour. They can also combine these iridescent hues with those of the chromatophores to make shimmering purples and oranges, for example." (Brooks 2008:28)

Watch video
  Learn more about this functional adaptation.
  • Harun Yahya. 2002. Design in Nature. London: Ta-Ha Publishers Ltd. 180 p.
  • Brooks, Michael. 2008. Do you speak cuttlefish?. The New Scientist. 198(2653): 28-31.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:627Public Records:550
Specimens with Sequences:599Public Species:42
Specimens with Barcodes:599Public BINs:60
Species:43         
Species With Barcodes:42         
          
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Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Sepiida

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Barcode data

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Source: Barcode of Life Data Systems (BOLD)

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