Architeuthid families

Introduction

Architeuthid families consist of only two families, Architeuthidae and Neoteuthidae. Original evidence for placing these taxa together was based on morphology due mostly to the similarities of the fin attachment to the mantle, attachment of the buccal connective to arms IV and similarities of the club carpus (Roper & Young, 1972). However, recent molecular data by Lindgren (2010) and Lindgren et al., (2012) strongly support the close relationship between these two families.

Brief diagnosis:

An oegopsid with fins ...

• lacking free anterior lobes.
• attached anteriorly mostly to the muscular mantle (via fin cartilage and shell sac), not to the gladius.
  

Characteristics

1. Fins
   1. Anterior fin lobes absent.
      
   2. Most of fin attaches to dorsolateral side of muscular mantle not gladius.
      
   

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   Figure. Dorsal view of the fins showing absence of free lobes and attachment to mantle muscle. Left - Architeuthis dux, 57 mm ML. Drawing from Roper and Young, 1972. Right - Neoteuthis thielei, 83 mm ML. Drawing from Young, 1972. Both features of the fin are readily seen in the A. dux drawing; in the N. thielei drawing an arrow indicates the anterior attachment point of the fin.
   

2. Tentacles
   1. Numerous suckers present in the carpal region of the tentacle club.
   

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   Figure. Oral view of the carpal region of the tentacular club. Left - Large Architeuthis dux. Right - Alluroteuthis antarcticus, 32 mm ML. Photographs by R. Young.
   

   The usefullness of this character is supporting the relationship between these two families is uncertain. While the presence of numerous suckers in the carpal region is very unusual, in Architeuthis all of these suckers are paired with carpal knobs while in Alluroteuthis (and other neoteuthids) the carpal knobs (arrows) occur only along the dorsal margin of the carpal region where they are paired with distinctive carpal suckers.
   

3. Attachment of buccal connectives
   1. Buccal connectives attach to the dorsal margins of arms IV.
      

   This is an important phylogenetic character but of more general value as it is shared by the Lycoteuthidae, Enoploteuthidae, Ancistrocheiridae, Pyroteuthidae, Histioteuthidae, Psychroteuthidae, Ommastrephidae, Neoteuthidae and Bathyteuthdae.
   

Discussion of Phylogenetic Relationships

On morphological grounds the relationship between the Architeuthidae and Neoteuthidae as indicated by Roper and Young (1972) is weak, however, it is stronger between these two families than either is to any other oegopsid family.

Lindgren (2010) and Lindgren et al. (2012, using molecular techniques, found also that the Architeuthidae and Neoteuthidae grouped together, with strong support. The relationship between the architeuthid families and other oegopsid families was less clear. The 2010 study found them grouping with the histioteuthid families in two of their three analyses (the other analysis was unable to determine a relationship within the Oegopsida) while the 2012 study found that they grouped most closely with the Lycoteuthidae but with weak support for the latter.

References

Lindgren, A.R. 2010.Molecular inference of phylogenetic relationships among Decapodiformes (Mollusca: Cephalopoda) with special focus on the squid Order Oegopsida. Mol. Phylogenet. Evol. 56: 77-90.

Lindgren, A. R., M. S. Pankey, F. G. Hochberg and T. H. Oakley. 2012. A multi-gene phylogeny of Cephalopoda supports convergent morphological evolution in association with multiple habitat shifts in the marine environment. BMC Evolutionary Biology 2012, 12:129-144.

Verrill, A. E. 1879. The cephalopods of the north-eastern coast of America. Part I. The gigantic squids (Architeuthis) and their allies; with observations on similar large species from foreign localities. Trans. Connecticut Acad. Sciences 5:23:177-257.

Young, R. E. 1972. The systematics and areal distribution of pelagic cephalopods from the seas off Southern California. Smithson. Contr. Zool., 97: 1-159.