Bivalvia taxonomy

From Palaeos.org

Jump to: navigation, search
m
(removed phylogeny plaque at top, added taxonomy of ''Invertebrate Fossils'' text)
Line 1: Line 1:
-
{{Bivalvia}}
+
:: ''For bivalvian phylogeny see'' [[Bivalvia phylogeny]]
-
 
+
-
<center><big><big><big>Bivalvia Systematics and Classification</big></big></big></center>
+
-
 
+
Many diverse schemes have been developed for the classification of bivalves. For a long time, experts used only one characteristic feature, such as shell morphology and hinge type, or type of gills. This led to a number of disparate systems.  The most popular and widely adapted of these was that of Newell in the Treatise on Invertebrate Paleontology Moore [ed.] (1969), which employs a system based on general shell shape, microstructures and hinge configuration. Features such as hinge, dentition, mineralogy, and shell structure and composition do not appear to be characters of much adaptive significance among bivalves, and hence change slowly and can be used for defining major taxonomic groups.
Many diverse schemes have been developed for the classification of bivalves. For a long time, experts used only one characteristic feature, such as shell morphology and hinge type, or type of gills. This led to a number of disparate systems.  The most popular and widely adapted of these was that of Newell in the Treatise on Invertebrate Paleontology Moore [ed.] (1969), which employs a system based on general shell shape, microstructures and hinge configuration. Features such as hinge, dentition, mineralogy, and shell structure and composition do not appear to be characters of much adaptive significance among bivalves, and hence change slowly and can be used for defining major taxonomic groups.
Line 43: Line 40:
Burrowing or boring forms, very modified, with aragonitic shells and desmodont dentition. Gills eulamellibranchiate or, in the Superfamily Poromyoidea septbranch.  
Burrowing or boring forms, very modified, with aragonitic shells and desmodont dentition. Gills eulamellibranchiate or, in the Superfamily Poromyoidea septbranch.  
* Order Pholadomyoida  
* Order Pholadomyoida  
 +
 +
====Taxonomy of R. C. Moore, 1952 ====
 +
R. C. Moore, in Invertebrate Fossils, pub. 1952, (Ch  Pelecypods) provides a straight forward and logical classification of the higher bivalve taxa based on characters of the hinge line and shell structure. While this classification may have been subject to revision based on further anatomical and organo-chemical studies, it remains useful as a way of organizing the taxa in this group of molluscan animals; the main advantage being that the defining characters of readily discernible by anyone.
 +
 +
This classification, given as that of pelecypods, divides the class into two subclasses based on the structural composition of the shell and 8 orders based on characters of the hinge line and teeth.  Orders are further broken into suborders based on special or modifying characters. 
 +
 +
'''Subclass Prionodesmacea''' Pelecypods with a prismatic and nacreous shell structure; mantle lobes separate, siphons poorly developed, hinge teeth lacking or poorly specialized.  ''Ordovician - Rec''
 +
 +
*Order Palaeoconcha  Gills protobranch, hinge teeth missing or poorly defined, adductors subequal.      ''Ordovician - Rec''
 +
*O. Toxodonta       Hinge teeth small, numerous, all similar. ''Ordovician - Rec''
 +
**Suborder Nuculacea  Toxodonts with protobranch gills. ''do''
 +
**sO. Arcacea  Toxodonts with filibranch gills.  ''do''
 +
*O. Schizodonta.      Hinge teeth few and distinct, diverge from beneath the beak. Gills filibranch. ''Ordovician - Rec''
 +
**sO. Trigoniacea Marine schizodonts with a trigonal shell.  ''do''
 +
**sO. Cardiniacea Shell rounded to elongate, mostly fresh water.  ''Silurian - Rec''
 +
*O. Dysodonta Hinge teeth weak lacking. Gills filibranch in some, eulamellibranch in others.  ''Ordovician - Rec''
 +
**sO. Mytilacea   Slipper shells and related; filibranch.  ''Ordovician - Rec''
 +
**sO.  Pectinacea Scallops; filibranch.  ''do''
 +
**sO.  Pinnacea  Thin, elongate shells with terminal beaks and eulamellibranch gills. ''Devonian - Rec''
 +
**sO.  Limacea   Resemble Pectinacea, eulamellibranch. ''Pennsylvanian - Rec''
 +
**sO.  Ostracea   Oysters, eulamellibranch. ''Triassic - Rec''.
 +
**sO.  Dressensiacea Like mytilids but with eulamellibranch gills.  ''Eocene - Rec''.
 +
 +
*O. Isodonta Prionodesmacea with filibranch gills and a pair of symmetrically placed teeth on each valve.  ''Triassic - Rec''. 
 +
**sO. Spondylacea  Isodonts with spiny inquevalved shells.  ''Triassic - Rec''. 
 +
**sO. Anomiacea       Thin shelled isodonts, the lower valve commonly perforate. ''Jurassic - Rec.''
 +
 +
'''Subclass Teleodesmacia''' Pelecypods having a porcelaneous and in part nacreous structure to the shell. In living forms all are eulamellibranch, except for the Poromyacea which are septibranch; mantle lobes are generally connected, siphons well developed. ''Ordovician - Rec.''
 +
*O. Desmodonta Burrowing and boring Teleodesmacea with weak hinge teeth and a resilifer for an internal ligament ''Ordovician - Rec''.
 +
**sO. Anatinacea    Desmodonts with hinge teeth and internal ligament poorly developed  ''Ordovician - Rec''.
 +
**sO.  Myacea     Desmodonts with shells that gape posteriorly, and have elongate siphons. ''Triassic - Rec''.
 +
**sO.  Adesmacea    Rock borers and wood borers.  ''Jurassic - Rec''. 
 +
::sO.  Matratacea Cardinal teeth retained, siphons prominent  ''Cretaceous - Rec''
 +
**sO. Ensipnonacea Shell degenerate, siphons enclosed in a calcareous tube. ''Cret -Rec''.
 +
**sO.  Solenacea Elongate razor clams. ''Cret -Rec''.
 +
::: All above suborders have eulamellibranch gills, (in living forms).
 +
**sO. Porodesmacea Borers with septibranch gills    ''Jurassic - Rec''.
 +
 +
Gill structure in fossil forms is conjectural, except for the fact that the same basic eulamellibranch structure is found in all suborders, except in the septibranch Porodesmacea, showing that it is a common trait and therefore most likely ancestral. Alternatively eulamellibranch gills may have evolved separately from filibranch in the different suborders at different times due to similar environmental pressures, provided of course these groups are valid monophyletic taxa.
 +
 +
*O.  Heterodonta    Arch typical clams with hinge teeth that include well developed cardinals.
 +
''Silurian - Rec''.
 +
**sO. Cypricardinacea Primitive, generalized heterodonts.  ''Silurian - Rec''.
 +
**sO. Lucinacea    Evolved heterodonts with two cardinal teeth on each valve.  ''Silurian - Rec''
 +
**sO. Cyrenacea     Further evolved heterodonts with three cardinal teeth on each valve.  ''Triassic - Rec''.
 +
 +
The Lucinacea and Cyrenacea are further distinguished from each other by their lateral teeth. In the Lucinacea there is a single tooth near each extremity of the hinge line on the right hand valve, two on the left hand, all set at an angle to the surface of the shell so as to diverge outwardly. In the Cyrenacea there are two teeth near each extremity of the hinge on the right hand valve, one on the left, all set running in the direction of the hinge, parallel to the shell.
 +
 +
*O. Pachyodonta     Mostly thick shelled, specialized,inequivalved sedentary clams with thick hinge teeth.  ''Jurassic - Rec''.
 +
**sO. Chamacea     Pachyodonts retaining indication of heterodont origin.  ''Jurassic - Rec''.
 +
**sO. Rudistacea    Derived, specialized pachyodonts that include robust coral-like forms. ''Cretaceous''
 +
 +
Rudistid clams (Rudistacea) were important reef builders during the Early Cretaceous.
 +
==Links==
==Links==
Line 49: Line 100:
==Credits==
==Credits==
MAK020926 [http://www.palaeos.com/Invertebrates/Molluscs/Bivalvia/Bivalvia.html Palaeos com]
MAK020926 [http://www.palaeos.com/Invertebrates/Molluscs/Bivalvia/Bivalvia.html Palaeos com]
 +
John M 3/3/11- Taxonomy of R.C. Moore, 1952

Revision as of 16:48, 3 March 2011

Personal tools