Enoploteuthid families

Introduction

Four families show close relationships and are placed here in a clade "enoploteuthid families." A formal name is premature, however, until the position of the clade within the Oegopsida and confirmation of the monophyletic nature of the group at this position can be confirmed.

Members of this clade are small squids that occupy the mesopelagic zone of the ocean and have an abundance of photophores. Three of the four families have hooks on the arms and, usually, tentacles.

Brief diagnosis:

An oegopsid ...

• with eight or remnants of eight buccal supports.

Characteristics

1. Arms
1. Armature in two series.
2. Arm hooks present except in Lycoteuthididae.
   1. Aperature absent (except for small aperature in Enoploteuthis).
   2. Belly of hook with ridge (except in Pterygioteuthis).
   3. Margin of hook base with 2 large lateral lobes and 1 proximal lip.
   4. Skirt absent.
   5. Accessory hooks absent.
   **See Cephalopod Hooks for hook terminology.
   
   
2. Tentacles
   1. Armature on tentacular clubs in four series in young but may be reduced on manus in subadults.
   2. Club hooks present except in Lycoteuthidae and Pterygioteuthis.
   3. Proximal (= carpal) locking-apparatus of tentacle compact, often circular.
      
      
3. Buccal crown
1. Buccal crown with eight or remnants of eight buccal supports.
2. Buccal-crown connectives attach to dorsal margins of arms IV.
   
   
4. Photophores
   1. Numerous photophores present but distribution varies between families.
      
      
5. Spermatangia attachment-sites
   1. Spermatangia attach to specialized tissue in nuchal region (except Enoploteuthis).
      
      
6. Gladius
   1. Gladius with conus and/or elongate conus field.

Comments

The table compares some familial characteristics of subadults of the enoploteuthid families.

Discussion of Phylogenetic Relationships

Young and Harman (1998) in a morphological, cladistic study demonstrated that the relationship between the Lycoteuthididae and the Pyroteuthididae was closer than the relationship between the Pyroteuthididae and the Enoploteuthididae. This conclusion favored the breakup, as proposed by Clarke (1988), of the former Enoploteuthididae which had included the subfamilies Pryoteuthidinae, Ancistrocheiridinae and Enoploteuthidinae. Among the features that support a sister-group relationship between the Pyroteuthididae and Lycoteuthididae is the remarkable similarity in the structure and the position of the photophores (the structural similarity was first noted by Herring et al., 1985).

Support for a Enoploteuthid-Lycoteuthid-Pyroteuthid clade was provided by the shared presence of:

• Buccal membrane papillae.
• Collagen light-guides in photophores.

• Ring-canal connects buccal pockets.
• Photophores structure unique (i.e., double nature of certain tentacular photophores; microvillous blood vessels within photogenic tissue).
• Photophores arrangement (i.e., tentacular, ocular, anal, branchial, abdominal photophores).
• Similar site for spermatophore receptacles (not included by Young and Harman (1998).
  

The study suffers primarily from polarization uncertainities due to poor understanding of outgroup relationships. The study suggests that the pyroteuthids have diverged strongly in morphology from their nearest relatives.

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.

Herring, P. J., P. N. Dilly and C. Cope. 1985. The photophore morphology of Selenoteuthis scintillans Voss and other lycoteuthids. J. Zool. Lond., 206: 567-589.

Young, R. E. and R. Harman. 1998. The phylogeny of the "enoploteuthid families." Smithson. Contr. Zool., No. 586: 257-270.