The association between distribution and octopodid morphology: implications for classification

The Octopodidae occur in virtually all benthic marine habitats; however, species in the family show little overt morphological differentiation. Subfamilies are currently defined by the presence or absence of an ink sac and the number of sucker rows (the presence of an ink sac and a single row of suckers are primitive characters) (Voss, 1988b); subfamily depth ranges arc cited in the diagnoses. Examination of external octopodid morphology through principal components analysis reveals that octopodid morphology correlates with geographic distribution. Low-latitude, shallow-water octopuses typically have narrower bodies and larger suckers on longer arms than do deep sea and high-latitude species. Sucker size inversely correlates with depth distribution, as studies of sucker functional morphology predict (Kier & Smith, 1990). The same characters contribute in a very similar manner to the discrimination of species when grouped by subfamily and when grouped by mean depth distribution. That depth distributions, which correlate with morphology and with the loss of the ink sac, contribute to the definition of these subfamilies, suggests that the subfamilies constitute phenetically similar rather than monophyletic groups. Cladistic analysis is required to reassess octopodid phylogeny.     

MORPHOLOGICAL DEFORMATION IN PRESERVED SPECIMENS OF THE DEEP-SEA OCTOPUS GRANELEDONE

Although morphology of firm-bodied shallow-water octopuses resistspreservation-linked deformation, preservation and handling of deep-seaspecimens of Graneledone are hypothesized to deform specimensby accelerating fluid loss from mantle and arm tissues. Principalcomponents analysis finds that seven of 39 North Pacific specimensof the genus are exceptionally narrow; the remaining specimensshow considerable morphological variation, independent of timein preservation. Five exceptionally narrow specimens, including someparatypes of G. pacifica, were collected and preserved by thesame trawling study; a single unrecorded factor in their common preservationhistory may have caused their deformation. The high morphologicalvariation among the remaining specimens, seemingly unique amongoctopodids, may reflect factors as subtle as how the specimenwas stored in the jar. Two types of change with time in preservationare documented. The mantle wall of formalin-fixed specimensthins unpredictably after storage for 30 months in 70% ethanol,consistent with deformation in preservation. Skin tubercles onthe dorsal mantle, important taxonomic characters, become more prominentduring the first decade in preservation. To maximize the informationspecimens with fluid-rich tissues convey and to identify thesources of deformation, the full preservation history and measurementsmade prior to dissection should be permanently recorded. (Received 25 April 2000; accepted 25 July 2000)     

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.