Sepiolidae Leach 1817

The phylogenetic tree is based on relationships suggested by Naef (1923) and conjecture based on comments given below.

Introduction

Sepiolids are small (ca. 1-10 cm ML), broad cephalopods with a rounded posterior mantle and ear-like fins. Species of the Rossinae and Sepiolinae are benthic while those of the Heteroteuthinae are pelagic. The most distinctive group is the Heteroteuthinae in which the ventral mantle margin extends beneath the head, and the photophores are fused into a single large organ. All sepiolids, where known, lay large benthic eggs and the young hatch out at an advanced stage of development and their length may be one quarter of that of the adult female (Naef, 1921-23).

Diagnosis

A Sepiolida ...

• with funnel locking-apparatus with a single depression.

Characteristics

1. Arms
   1. Any or all of the dorsal six arms may be hectocotylized.
      
      
2. Funnel
   1. Funnel locking-apparatus often with an elongate, broad groove, but considerable variability may exist.
      
      
3. Mantle
   1. Dorsal margin fused to or free from head.
      
      
4. Shell
   1. Shell a thin or rudimentary gladius or absent.

Comments

The following table compares the three subfamilies and Choneteuthis whose subfamily is uncertain.

The NewSubFamily does not fit well in the Order Sepioidea as two basic sepioid characters (eyes with secondary eyelids; funnel with lateral adductor muscles) are missing. Our first impression was that the NewSubFamily was more closely related to the Myopsida. However, many features commonly associated with the Sepioidea (absence of an interstellate connective, gills apparently without a branchial canal) and the Sepiolidae (globular sucker rings, general shape, fusion of the head and mantle in the nuchal region) convince us that its closest relationships belong within the Sepiolidae. The most convincing character is the presence of a ventral mantle adductor muscle which is common to members of the Sepiolida. The ventral mantle adductor in NewSubFamily is very weak and barely recognizable. This condition has led us to suspect that the absence of the two basic Sepioid characteristics listed above is due to loss. At present, the phylogenetic position of the NewSubFamily is guesswork since the phylogeny of the Sepiolida is in flux.

Choneteuthis tongaensis may be derived from an ancestral line leading to Sepiolina-like species and then to the remaining Heteroteuthinae. It has the heteroteuthin shield and silvery sides but lacks a tentacle organ, as does Sepiolina, but also lacks the web between arms I-III.

Nomenclature

A list of all nominal genera and species in the Sepiolidae can be found here. The list includes the current status and type species of all genera, and the current status, type repository and type locality of all species and all pertinent references.

Discussion of Phylogenetic Relationships

Naef (1921-3) divided the Sepiolidae into three subfamilies and placed Sepiolina in the Sepiolinae. We place it in the Heteroteuthinae. As Naef (1921-23) recognized, characteristics of this genus place it right between the two subfamilies. Choneteuthis which is presently not placed in any subfamily shows strong similarities to Sepiolina especially in having a large visceral photophore and ventral shield and lacking a tentacular organ. The latter feature is primarily responsible for separating Sepiolina from the remainder of the Heteroteuthinae.   Choneteuthis further confuses the boundries of the Heteroteuthinae.

A cladistic analysis has not been made on this family but one is badly needed as much disagreement exists over classification. Clarke (1988) includes this family and the Idiosepiidae in the Order Sepiolida. Fioroni (1981) includes this family in the Order Sepioloidea and includes the Idiosepiidae as a subfamily of the Sepiolidae.

References

Clarke, M. R. 1988. Evolution of recent cephalopods -- A brief review. P. 331-313. In: Clarke, M. R. and E. R. Trueman (Eds.). The Mollusca. Vol. 12. Paleontology and Neontology of Cephalopods. Academic Press, New York. 355pp.

Fioroni, P. 1981. Die Sonderstellund der Sepioliden, ein Vergleich der Ordnungen der rezenten Cephalopoden. Zool. Jahrb., 108: 178-228.

Lu, C. C., A. Guerra, F. Palumbo and W. C. Summers. 1992. Order Sepioidea Naef, 1916. In: Sweeney, M. J., C. F. E. Roper, K. M. Mangold, M. R. Clarke and S. V. Boletzky (eds.). "Larval" and juvenile cephalopods: a manual for their identification. Smithson. Contr. Zool. No. 513: 1-282.

Naef, A. 1921/23. Cephalopoda. Fauna e Flora del Golfo di Napoli. Monograph, no. 35. English translation: A. Mercado (1972). Israel Program for Scientific Translations Ltd., IPST Cat. No. 5110/1,2.

Nesis, K. N. 1982. Abridged dey to the cephalopod mollusks of the world's ocean. 385+ii pp. Light and Food Industry Publishing House, Moscow. (In Russian.). Translated into English by B. S. Levitov, ed. by L. A. Burgess (1987), Cephalopods of the world. T. F. H. Publications, Neptune City, NJ, 351pp.