Cephalopoda

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(Systematics: Removed Teichert 1988 ref in text, removed to References.)
(Systematics: revisted 1st part of 3rd par , soft part classif of recent forms, shell based of fossil forms)
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The Subclass Nautiloidea forms a large and diverse, all be it paraphyletic, group, divisable into phyllogenetically defined superorders (or infraclasses). All nautiloids are united by the fact they have simple, adorally concave septa, retrosiphonate septal necks, sutures that are never elaborate,and are descended from a common ancestor, ''Plectronoceras'' They are more than simply cephalopods that are neither ammonoids or coleoids.  
The Subclass Nautiloidea forms a large and diverse, all be it paraphyletic, group, divisable into phyllogenetically defined superorders (or infraclasses). All nautiloids are united by the fact they have simple, adorally concave septa, retrosiphonate septal necks, sutures that are never elaborate,and are descended from a common ancestor, ''Plectronoceras'' They are more than simply cephalopods that are neither ammonoids or coleoids.  
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Thus, while there is some agreement regarding recent cephalopods, the classification of the various extinct forms is very uncertain, precisely due to this fact that (with one or two rare exceptions known from the Devonian, and a Jurassic ammonite that preserved muscle attachment scars) the soft body parts are not known.  The following list basically follows Teichert (1988) with the Palcephalopoda/Neocephalopoda hypothesis incorporated; except that Teichert's two Subclasses '''Endoceratoidea''' and '''Actinoceratoidea''' have been discarded, since the two orders [[Endocerida]] and [[Actinocerida]] are probably not so distinct from their contemporaries as to justify such a high taxonomic ranking.
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While there is general agreement regarding classification of recent cephalopods, mostly coleoids, based on soft part anatomical features, classification of extenct fossil forms based on such criteria is impossible other than for a few inferences that night be drawn from preserved muscle attachment scars, preserved radula, tentacle imprints, and isolated body impressions. Hard part, shell based features on the other hand provide the basis for a relable, phylogenetically plausable  and generally accepted classifiation of extinct forms.   
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The following list basically follows Teichert (1988) with the Palcephalopoda/Neocephalopoda hypothesis incorporated; except that Teichert's two Subclasses '''Endoceratoidea''' and '''Actinoceratoidea''' have been discarded, since the two orders [[Endocerida]] and [[Actinocerida]] are probably not so distinct from their contemporaries as to justify such a high taxonomic ranking.
===Class Cephalopoda===
===Class Cephalopoda===

Revision as of 01:03, 3 September 2009

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