num. 7-12 dicembre 2007





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Ctelonia

Pecten flexuosus
 
Pecten glaber
     
11
 
12
 
21
 
22
     
13
 
14
 
23
 
24
     
15
 
16
 
25
 
26
Flexuosus

4 to 5 teeth which tend to sink in the shell at adult stage (pics 11 & 15) and are prominent when young (pics 14 & 16).
The byssal notch is deep and quadrangular.

Glaber

5 (younger) to 7 (older) teeth. The teeth don't sink.
The younger the shell, the more prominent they are.
The byssal notch is triangular.

In adult shells of both species, a calcareous extension tends to separate the ctelonium from the outside world (pics 11, 13, 15, 25 & 26).

additional distinctive features

Flexopecten flexuosus:

The auricular trench is deeper than in glaber, and is prominent in the inner side.
The margins smooth out the inner relief of the valves (ribs, undulations).
The growth lines are never noticeable.
The byssal notch is quadrangular and deep.

Flexopecten glaber:

Inner furrow sometimes appearing behind the auricular trench, whose wall in thinner than in flexuosus.
The inner relief of the valves is more accentuated near the margins than elsewhere.
The growth lines can give to the shell a cancellated sculpture near the umbos.
The byssal notch is triangular.

Some other features don't seem useful, or usable, and won't be repeated (auricular wing flatter here than there etc.)
Flexuosus

4 to 5 teeth which tend to sink in the shell at adult stage (pics 11 & 15) and are prominent when young (pics 14 & 16).
The byssal notch is deep and quadrangular.

Glaber

5 (younger) to 7 (older) teeth. The teeth don't sink.
The younger the shell, the more prominent they are.
The byssal notch is triangular.

In adult shells of both species, a calcareous extension tends to separate the ctelonium from the outside world (pics 11, 13, 15, 25 & 26).

additional distinctive features

Flexopecten flexuosus:

The auricular trench is deeper than in glaber, and is prominent in the inner side.
The margins smooth out the inner relief of the valves (ribs, undulations).
The growth lines are never noticeable.
The byssal notch is quadrangular and deep.

Flexopecten glaber:

Inner furrow sometimes appearing behind the auricular trench, whose wall in thinner than in flexuosus.
The inner relief of the valves is more accentuated near the margins than elsewhere.
The growth lines can give to the shell a cancellated sculpture near the umbos.
The byssal notch is triangular.

Some other features don't seem useful, or usable, and won't be repeated (auricular wing flatter here than there etc.)
Acknowledgements ?

Of course, acknowledgements !
Many thanks to Carlos Duares de Carvalho who gave me the pics I missed to begin.
And I must not forget Paolo G. Albano who gave me many glaber from northern Adriatic.

Thanks to all and now followin pages for more image details