the Pinnidae family, which comprises three living genera, Atrina, Pinna, and
Streptopinna, and seven fossil ones. The Pinnidae family comprises 123 living
and fossil species and subspecies. The Pinna genus itself comprises 75 extant and
extinct species and subspecies. The living species all together have a broad geographic repartition all over the world, with a predilection for warm waters. For a
detailed list of the species that belong to the Pinna genus, we refer to the following
Web site: http://zipcodezoo.com/Key/Animalia/Pinna_Genus.asp.
According to Taylor et al. (1969) and Carter (1990), the Pinnidae family
is of Paleozoic origin, and appeared at the basal Carboniferous. Genera like
Aviculopinna, Meekopinna, or Pteronites, and species like Pinna peracuta or
Pinna flexistria are attested to be of Carboniferous age. The Pinnid family may
derive from Devonian pterineids, such as Leptodesma (Carter 1990). The family
has a discontinuous fossil record. The well-known Trichites genus, characterized by
an extremely thick calcitic prismatic layer, is frequent in the calcareous sediments
of the Upper Jurassic (Tithonian).
13.3 Shell Formation Process
13.3.1 Shell Growth
As shown in Fig. 13.1, the shell of Pinna nobilis has a typical elongated triangular
shape with a sharp anterior. The shell is equivalve. The color of the shell is light
brown for juvenile specimens and becomes brown-red when the shell thickens. This
coloration, localized exclusively in the outer shell layer, is due to a mixture of
carotenoid pigments (Gauthier et al. 1994), the exact molecular characterization of
which has still to be done. In juvenile specimens, the shell is translucent
(Fig. 13.1b), but becomes opaque with age.
Like several bivalves of Mediterranean or temperate zones, the shell growth of
P. nobilis follows a seasonal pattern: the shell grows slowly during the cold months
and has a maximal growth during late spring and early summer (Katsanevakis
2007). This optimum may result from a combination of temperature and food
availability. When the water temperatures exceed a threshold (around 29
C) during
August, the shell growth slows down or stops. The growth of the shell, which has
been monitored during the entire life of several specimens, follows a classical Von
Bertalanffy model, with a rapid almost linear growth during the first 3 years, and a
progressive decrease of the growth rate until reaching a plateau (Moreteau and
Vicente 1982). An equation was formulated to describe the mean shell growth:
H t ¼ 86:3 1 À e
À0:053 tþ0:22
ð
Þ
Â
Ã
where H t is the full length, and t, the age in months.
According to this equation, a 1-year-old specimen reaches 12 cm, a 2-year-old,
22 cm, a 3-year-old, 30 cm. At these early stages, the shell remains very thin; it is
extremely fragile and translucent. 20-year-old specimens are about 80 cm long, and
the shell thickness is about 1 cm at the tip. More recent studies on different
358
F. Marin et al.
Streptopinna, and seven fossil ones. The Pinnidae family comprises 123 living
and fossil species and subspecies. The Pinna genus itself comprises 75 extant and
extinct species and subspecies. The living species all together have a broad geographic repartition all over the world, with a predilection for warm waters. For a
detailed list of the species that belong to the Pinna genus, we refer to the following
Web site: http://zipcodezoo.com/Key/Animalia/Pinna_Genus.asp.
According to Taylor et al. (1969) and Carter (1990), the Pinnidae family
is of Paleozoic origin, and appeared at the basal Carboniferous. Genera like
Aviculopinna, Meekopinna, or Pteronites, and species like Pinna peracuta or
Pinna flexistria are attested to be of Carboniferous age. The Pinnid family may
derive from Devonian pterineids, such as Leptodesma (Carter 1990). The family
has a discontinuous fossil record. The well-known Trichites genus, characterized by
an extremely thick calcitic prismatic layer, is frequent in the calcareous sediments
of the Upper Jurassic (Tithonian).
13.3 Shell Formation Process
13.3.1 Shell Growth
As shown in Fig. 13.1, the shell of Pinna nobilis has a typical elongated triangular
shape with a sharp anterior. The shell is equivalve. The color of the shell is light
brown for juvenile specimens and becomes brown-red when the shell thickens. This
coloration, localized exclusively in the outer shell layer, is due to a mixture of
carotenoid pigments (Gauthier et al. 1994), the exact molecular characterization of
which has still to be done. In juvenile specimens, the shell is translucent
(Fig. 13.1b), but becomes opaque with age.
Like several bivalves of Mediterranean or temperate zones, the shell growth of
P. nobilis follows a seasonal pattern: the shell grows slowly during the cold months
and has a maximal growth during late spring and early summer (Katsanevakis
2007). This optimum may result from a combination of temperature and food
availability. When the water temperatures exceed a threshold (around 29
C) during
August, the shell growth slows down or stops. The growth of the shell, which has
been monitored during the entire life of several specimens, follows a classical Von
Bertalanffy model, with a rapid almost linear growth during the first 3 years, and a
progressive decrease of the growth rate until reaching a plateau (Moreteau and
Vicente 1982). An equation was formulated to describe the mean shell growth:
H t ¼ 86:3 1 À e
À0:053 tþ0:22
ð
Þ
Â
Ã
where H t is the full length, and t, the age in months.
According to this equation, a 1-year-old specimen reaches 12 cm, a 2-year-old,
22 cm, a 3-year-old, 30 cm. At these early stages, the shell remains very thin; it is
extremely fragile and translucent. 20-year-old specimens are about 80 cm long, and
the shell thickness is about 1 cm at the tip. More recent studies on different
358
F. Marin et al.