CLADISTIC ANALYSIS OF THE OCTOPODS BASED ON ANATOMICAL CHARACTERS

Parsimony analysis of 29 finned and finless octopod taxa considered66 anatomical and morphological characters to discover synapomorphiesthat unite monophyletic groups. The resultant cladogram (177equally parsimonious trees at 191 steps, CI 0.429) resolvedall relationships except those among the 16 exemplars of theOctopodidae included and those among Tremoctopus, Ocythoe andArgonauta. Bootstrap values of over 90% support the monophylyof the finned and finless octopods, relationships among thefinned octopods, the bolitaenids and the monophyly of Haliphron,Tremoctopus, Ocythoe and Argonauta; bootstrap values for othernodes range from 57 to 79%. Among finned octopods, specimensrepresenting Grimpoteuthis are basal, as Voss (1988a) suggested.Specimens of Opisthoteuthis represent a distinct lineage, andare sister taxon, in this analysis, of Cirroteuthis (althoughspecimens of Stauroteuthis could not be included). New definitionsof the genera Opisthoteuthis and Grimpoteuthis are providedto reflect their separate evolutionary histories rather thantheir overt morphological similarity. Among finless octopods,bolitaenids are basal. The monophyletic Octopodidae is the sistertaxon to the clade containing the sister taxa Vitreledonellaand Amphitretus, and Haliphron, Tremoctopus, Ocythoe and Argonauta.The Ctenoglossa and Heteroglossa, families grouped by sharedradular dentition, are diphyletic and paraphyletic, respectively.The cladistic relationships demonstrate that both the Vitrele-donellidaeand Idioctopodidae are junior synonyms of the Amphitretidae;despite conspicuous morphological differences separating thesetaxa, they share a recent evolutionary history.