Cephalopoda

From Palaeos.org

Jump to: navigation, search
m (Systematics: spelling of Coleoidea)
(introduction and higher classification)
Line 1: Line 1:
-
  [[Cyrtosoma|CYRTOSOMA]]
+
'''Cephalopods''' (Class Cephalopoda)are exclusively marine mollusks (Phyllum [[Mollusca]]) with well developed prehensile grasping appediges the encircle the mouth and protrude from a well defined head, and which have a well developed nervous system. All are carnivorous. Other mollusks include [[Gastropoda|gastropods]], snails, [[bivalvia|pelecypods]], clams and other bivalves, and [[Scaphopoda|scaphopods]], tusk shells.   
 +
 
 +
===Higher Biological Classification===
 +
*Phyllum Mollusca
 +
** Class Cephalopoda
 +
*** Subclass [[Nautiloidea]]
 +
*** Subclass [[ Ammonoidea]]       
 +
*** Subclass  [[ Coleoidea]]
 +
 
 +
Most classification divide the Cephalopoda in the three subclasses as shown. Nautiloids are also known as Palcephalopoa, a term which is applied to most but not all members of the subclass.  Ammonoids and Coleoids and a few nautiloides come under the term Neocephalopoda. Both terms are based on the morphology and biology of living cephalopods, Palcephalopoda for the presumed primitive ''Nautilus'' and ''Allonautilus'', representing the nautilids and Neocephalopoda for the derived and presumed advanced coleoids.                 
 +
 
 +
 
 +
 
 +
[[Cyrtosoma|CYRTOSOMA]]
  |--+--[[Scaphopoda|SCAPHOPODA]]
  |--+--[[Scaphopoda|SCAPHOPODA]]
  |  `--'''CEPHALOPODA'''
  |  `--'''CEPHALOPODA'''
Line 61: Line 74:
The trouble with the anatomical scheme is that it is impossible to know from shell structure alone alone whether extinct forms had two or four gills, or anything really much about their soft body anatomy. From this it is apparent that the two-fold anatomical classification is inadiquate except in modern forms.   
The trouble with the anatomical scheme is that it is impossible to know from shell structure alone alone whether extinct forms had two or four gills, or anything really much about their soft body anatomy. From this it is apparent that the two-fold anatomical classification is inadiquate except in modern forms.   
-
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 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.  
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.   
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.   

Revision as of 00:34, 21 April 2010

Personal tools