Octopodiformes Berthold and Engeser, 1987

Introduction

The Octopodiformes consists of the Octopoda which contains over 200 species and the Vampyromorpha which contains a single species. The latter is a phylogenetic relict.

Characteristics

1. Arms
   1. True arms II modified or absent.
   2. True arms IV unmodified.
   3. Suckers radially symmetrical.
   4. Horny rings in suckers absent.
   5. Functional arms IV united by web (absent in some argonautoids).
      
      
2. Buccal crown
   1. Buccal crown absent.
      
      

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      Figure. Oral view of the region surrounding the buccal mass of Vampyroteuthis infernalis showing the absence of a buccal crown. Photograph by R. Young.

3. Head
   1. Outer statocyst capsule present.
   2. Superior buccal lobes adjacent (fused at edges) or completely fused to posterior buccal lobes.
   3. Inferior frontal lobe system of brain present or insepient.
      
      
4. Photosensitive vesicles
   1. Lie outside of cephalic cartilage: dorsal to funnel (Vampyromorpha) or on stellate ganglia in mantle cavity (Octopoda).
      
      
5. Fins
   1. When present, with cartilagenous axial support (only in juvenile fin of Vampyroteuthis).
      
      
6. Shell
   1. Shell a gladius, cartilage-like fin support, pair of stylets, or absent.
      
      
7. Viscera
   1. Nidamental glands absent.
   2. Crop usually present.
   3. Oviducal glands radially symmetrical.
   4. Digestive gland duct appendages lie "outside" nephridial coelom.
   5. Nephridial coeloms separate.

Origin of the Octopoda

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Drawing modified from Young, Vecchione and Donovan, 1999.

Naef (1923) felt that the origin of the Octopoda would "forever be obscure." But Naef was unaware of the significance of Vampyroteuthis which was believed to be a cirrate octopod at the time. We now know that the Vampyromorpha is the sister group of the Octopoda and that Vampyroteuthis provides telling clues to the origin of the octopods. Young, et al. (1999) suggest two possible methods for this origin as illustrated here. In one (benthic route) the pelagic ancestor becomes benthic in a horizontal attitude (similar to the sepiolids today) and subsequently the arms and mouth rotate under the head. In the other alternative (pelagic route) the pelagic ancestor develops an "oral" orientation (i.e. laterally spread arms) here pictured with the oral end downward (as in octopods today) and subsequently becomes benthic with the oral end down.

Evidence for the latter route is found in the structure of the brain. Octopods have a series of lobes in the brain, the inferior frontal lobe system, that is derived from the posterior buccal lobe. These lobes process complex chemotactile information from the arms. Vampyroteuthis has an "insipient" inferior frontal lobe system (J. Young, 1977). This bathypelagic animal apparently has a relatively advanced system for processing chemotactile information from the arms, one that surpasses that of shallow-living benthic decapods. Apparently Vampyroteuthis uses its arms in an unusual manner. Young, et al. (1999) suggest that like its immediate ancestor (a "pre-octopod"), associates with pelagic jellyfish or tunicates and uses its arms and suckers to adhere to and/or explore the surfaces of these gelatinous animals. That is, it has an oral orientation for contact with surfaces. The pre-octopod, then was pre-adapted for settling on the ocean floor in an oral-end down configuration. This oral orientation enabled octopods to become the effective crawling animals that most are today. However the manner in which Vampyroteuthis actually uses its arms and its possible association with gelatinous animals has yet to be demonstrated.

Young, et al. (1999) argue, therefore, that the benthic habitat was the primitive one within the Octopoda and that pelagic species, which comprise nine of the eleven octopod families, are secondarily pelagic. In the Cirrates, these authors point out the compaction of viscera, loss of jet propulsion, presence of a fully-formed inferior frontal lobe system, single oviduct, fusion of the head and mantle and reduction of the shell as evidence of a quasi-benthic ancestry. In the Incirrates, they point to the presence of corneas (or their remnants), absence of shell, fins and cirri, fully formed inferior frontal lobe system, probably stalked chorions and brooding as evidence of a fully-benthic ancestry.

Discussion of Phylogenetic Relationships

J. Z. Young (1989), on the basis of anatomical differences, removed the Cirrata from its traditional place in the Octopoda and put it in its own order, Cirroctopodida. Young and Vecchione (1996), however, using cladistic analyses demonstrated that the inclusion of the Cirrata and Incirrata in the Octopoda is justified. That is, the order Octopoda, including the suborders Cirrata and Incirrata is a monophyletic group. This conclusion was more recently strengthened by the inclusion of additional characters in the analyses (Young & Vecchione, 2002).

Nomenclature

A variety of names have been proposed for this group (e.g., Octobrachia, Fiorini, 1981; Octopodiformes, Berthold and Engeser, 1987; Vampyromorphoidea, Engeser and Bandel, 1988; Vampyropoda, Boletzky, 1992). Young, et al.(1999) concluded that Octopodiformes was the most appropriate.

References

Berthold, T. and T. Engeser (1987). Phylogenetic analysis and systematization of the Cephalopoda (Mollusca). Verh. Naturwiss. Ver. Hamburg, 29: 187-220.

Boletzky, S. v. 1992. Evolutionary aspects of development, life style, and reproductive mode in incirrate octopods (Mollusca, Cephalopoda). Revue suisse Zool. 99(4):755-770.

Engeser, T. and K. Bandel (1988). Phylogenetic classification of coleoid cephalopods. In: Wiedmann, J. and Kullmann, J. (Eds.), Cephalopods. Present and past. p105-115. Stuttgart

Fioroni, P. 1981. Die Sonderstellung der Sepioliden, ein Vergleich der Ordnungen der rezenten Cephalopoden. Zool. Jb. Syst., 108: 178-228.

Young, J. Z. 1989. The angular acceleration receptor system of diverse cephalopods. Phil. Trans. R. Soc. Lond. B 325: 189-238.

Young, R. E. and M. Vecchione. (2002). Evolution of the gills in the Octopodiformes. Bull. Mar. Sci., 71:1003-1018.

Young, R. E., M. Vecchione and D. Donovan. 1999. The evolution of coleoid cephalopods and their present biodiversity and ecology. South African Jour. Mar. Sci. (in press).