Argonautoida Naef, 1912

Introduction

All four families of the Argonautoida are pelagic although one (Alloposidae) is "associated" with the ocean floor. The families are primarily distinguished by an unusual means of copulation which involves transferring a detached hectocotylus from the male to the female. The clade includes gelatinous species as well as very muscular species.

Brief diagnosis:

An incirrate octopod ...

• with detachable hectocotylus.

Characteristics

1. Arms
   1. Arm suckers in two series (grade to single series near mouth in Haliphron).
   2. One of third arm pair entirely hectocotylized and enrolled in a sac or pouch prior to use.
   3. Hectocotylized arm autotomizes (i. e., detaches) during copulation.
      

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      Figure. Detached hectocotylus of Argonauta argo found wiggling among contents of a midwater trawl. Photograph (overexposed) by M. Vecchione.

2. Funnel
   1. Funnel-locking apparatus well developed but structure differs among families.
      
      
3. Sexual dimorphism
   1. Males much smaller than females; males dwarfs in three families.
      
      
4. Shell
   1. Internal shell present only in Alloposidae; shell lost in other families.
      
      
5. Radula
   1. Radula heteroglossan.

Discussion of Phylogenetic Relationships

Naef (1923) suggested that the argonautoid families were derived from the Octopodidae and presented a phylogeny, shown above in the title frame, based on the characteristics of the hectocotylus.

Voight (1997), in a cladistic study using mostly different characters, presented a less resolved phylogeny:

    \    ------ Alloposidae
     \  / ----- Argonautidae
      \/ /
       \/------ Ocythoidae
        \
         \----- Tremoctopodidae

References

Naef, A. 1921/23. Cephalopoda. Fauna und Flora des Golfes von Neapel. Monograph, no. 35.

Nesis, K. N. 1982. Abridged key 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.

Voight, J. R. 1997. Cladistic analysis of the octopods based on anatomical characters. J. Moll. Stud. 63: 311-325.