220
layer cells by a narrow (several microns) mesenchyme-fi lled space. Demineralized
hyaloine has the appearance of a thin, stratifi ed fi brillar material, suggestive of periodic deposition. To date the role of the epidermal cells in the formation of hyaloine
remains elusive. However, hyaloine is structurally and spatially comparable with
ganoine, and is similarly deposited in close proximity with the well-differentiated
basalmost epidermal cells,” (Sire et al. 2009 ; see also Sire 1993 ; Sire et al. 2002 ;
Sire and Huysseune 2003 ).
Cosmine This biological material is “a unique combination of dentine, enameloid
and, at least in the functional sense, some true bone with the pore-canal sensory
system, and is found only in certain early fi shes,” (Thomson 1975 ). Cosmine is one
of the few morphological and histological vertebrate structures that have no homologue among extant forms (Ørvig 1969 ). For example, dentine layers can be located
in the form of concentric lamellar fashion at the margins of the cosmine as in the
case of the fi sh Ectosteorhachis nitidus (Thomson 1975 ). In some species, “the
superfi cial covering of the cosmine is an enameloid layer that is partially penetrated
by the tips of the dentine tubules and, of course, is also perforated by the pore-cavity
openings,” (Thomson 1975 ; see also Borgen 1992 ). According to common suggestion, cosmine has both strengthening and protective function. Cosmine, at least in
Ectosteorhachis and probably also in other osteolepid fi shes, and is functionally
associated in resorption (Borgen 1989 ) regeneration with a basal layer of diffuse
true bony tissue. This is in addition to the dentine and enameloid that enclose the
pore-canal and pulp-cavity systems (Thomson 1975 ).
Here, the characterization of cosmine made by Thomson ( 1975 ):
“A unique feature of all cosmine is that although it is functionally a full constituent of the dermal skeleton, it is topographically and to a great extent developmentally independent of the underlying constituents. The cosmine often forms in large
sheets that extend over a large number of otherwise separate dermal elements, covering the sutures between them. In most osteolepid Rhipidistia, for example, the
whole of the skull is covered with a shiny cosmine surface broken only by the tiny
openings of the sensory pores, and no sign of the sutures between the dermal bone
is visible. This obviously creates problems when it comes to growth in area of the
units of the dermal skeleton. Thus, a second unique feature of cosmine in Dipnoi
and Rhipidistia is that it is subject to periodic total resorption and redeposition,
releasing the sutural regions for growth to occur and then covering them up again.
Because cosmine may constitute up to 10 % of the calcifi ed tissue in the body, the
total resorption and redeposition of the cosmine represents an event of major biological signifi cance to the animal,” (Thomson 1975 ; see also Meinke 1984 ;
Mondéjar–Fernández and Clément 2012 ). The origin of cosmine in fi sh seems to be
ancient. For example, cosmine with locations in both dermal bones and scales has
been reported in one of the oldest lungfi sh from the Lower Devonian Uranolophus
wyomingensis (Meinke 1986 ) (Fig. 4.2 ).
Ganoine has been suggested to be either enamel proper or enameloid.
Correspondingly, it must be “homologous with the highly mineralized layer coating
the crown of vertebrate teeth” (Zylberberg et al. 1997 ; see for more information
4 Fish Scales as Mineral-Based Composites
layer cells by a narrow (several microns) mesenchyme-fi lled space. Demineralized
hyaloine has the appearance of a thin, stratifi ed fi brillar material, suggestive of periodic deposition. To date the role of the epidermal cells in the formation of hyaloine
remains elusive. However, hyaloine is structurally and spatially comparable with
ganoine, and is similarly deposited in close proximity with the well-differentiated
basalmost epidermal cells,” (Sire et al. 2009 ; see also Sire 1993 ; Sire et al. 2002 ;
Sire and Huysseune 2003 ).
Cosmine This biological material is “a unique combination of dentine, enameloid
and, at least in the functional sense, some true bone with the pore-canal sensory
system, and is found only in certain early fi shes,” (Thomson 1975 ). Cosmine is one
of the few morphological and histological vertebrate structures that have no homologue among extant forms (Ørvig 1969 ). For example, dentine layers can be located
in the form of concentric lamellar fashion at the margins of the cosmine as in the
case of the fi sh Ectosteorhachis nitidus (Thomson 1975 ). In some species, “the
superfi cial covering of the cosmine is an enameloid layer that is partially penetrated
by the tips of the dentine tubules and, of course, is also perforated by the pore-cavity
openings,” (Thomson 1975 ; see also Borgen 1992 ). According to common suggestion, cosmine has both strengthening and protective function. Cosmine, at least in
Ectosteorhachis and probably also in other osteolepid fi shes, and is functionally
associated in resorption (Borgen 1989 ) regeneration with a basal layer of diffuse
true bony tissue. This is in addition to the dentine and enameloid that enclose the
pore-canal and pulp-cavity systems (Thomson 1975 ).
Here, the characterization of cosmine made by Thomson ( 1975 ):
“A unique feature of all cosmine is that although it is functionally a full constituent of the dermal skeleton, it is topographically and to a great extent developmentally independent of the underlying constituents. The cosmine often forms in large
sheets that extend over a large number of otherwise separate dermal elements, covering the sutures between them. In most osteolepid Rhipidistia, for example, the
whole of the skull is covered with a shiny cosmine surface broken only by the tiny
openings of the sensory pores, and no sign of the sutures between the dermal bone
is visible. This obviously creates problems when it comes to growth in area of the
units of the dermal skeleton. Thus, a second unique feature of cosmine in Dipnoi
and Rhipidistia is that it is subject to periodic total resorption and redeposition,
releasing the sutural regions for growth to occur and then covering them up again.
Because cosmine may constitute up to 10 % of the calcifi ed tissue in the body, the
total resorption and redeposition of the cosmine represents an event of major biological signifi cance to the animal,” (Thomson 1975 ; see also Meinke 1984 ;
Mondéjar–Fernández and Clément 2012 ). The origin of cosmine in fi sh seems to be
ancient. For example, cosmine with locations in both dermal bones and scales has
been reported in one of the oldest lungfi sh from the Lower Devonian Uranolophus
wyomingensis (Meinke 1986 ) (Fig. 4.2 ).
Ganoine has been suggested to be either enamel proper or enameloid.
Correspondingly, it must be “homologous with the highly mineralized layer coating
the crown of vertebrate teeth” (Zylberberg et al. 1997 ; see for more information
4 Fish Scales as Mineral-Based Composites