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.

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 with circularis muscles.
      image info image info

      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.
      image info

      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.
      image info

      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).
      
      
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.
      image info

      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..