Sepioidea Naef, 1916

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.

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.
      

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      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).
      

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      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).
      

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      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 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.
      

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      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:

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*,

*these characters seem to be independently derived in a few Myopsida.