403
© Springer Science+Business Media Dordrecht 2015
H. Ehrlich, Biological Materials of Marine Origin, Biologically- Inspired Systems 4,
DOI 10.1007/978-94-007-5730-1_12
Chapter 12
Egg-Capsule Proteins of Selachians
Abstract Egg capsules of sharks, skates and chimaerods are made of very specifi c
collagen and polyphenol-based fi brillar structures, which exhibit unusual preservation
even when fossilized. The dogfi sh egg capsule is a composite material constructed
largely from collagen fi brils with a highly ordered, kinked molecular arrangement
set in a matrix containing spherical fi ller particles composed of hydrophobic protein. The capsule consists of collagenous three-dimensional very ordered open networks. This molecular construct is responsible not only for specifi c fi ltering
properties, but also for strength of the unique structured capsule. Both capsular collagen and polyphenol-based proteins possess high biomimetic potential.
The egg capsules of sharks and rays have been described previously by a number of
workers (Beard 1890 ; Widakowich 1906 ; Hussakof and Welker 1908 ; Clark 1922 ;
Hobson 1930 ; Whitley 1938 ; Nalini 1940 ; Brown 1955 ; Krishnan 1959 ). Also
attention has been paid to similar structures in Chimaeroids (Bessels 1869 ; Jaekel
1901 ; Gill 1905 ; Dean 1912 ; Brown 1946 ). The egg capsules of Elasmobranchii are
widely recognised as important in species identifi cation, and provide relevant information concerning their reproductive biology (Whitley 1939 ; Oddone et al. 2004 ).
According to the modern view, the “nidamental gland in contemporary elasmobranchs secretes a tertiary accessory envelope, called the egg capsule, around the
fertilized ova as they pass through the oviduct and into the uterus,” (Heiden et al.
2005 ). Except some rays, the encapsulation of fertilized eggs occurs in oviparous
and nearly all viviparous species (Hamlett and Koob 1999 ). Due to peculiar thickness, the egg capsules of oviparous species are exceptionally durable. The biological sense of these structures is to protect embryos during protracted development in
the marine environment (Hunt 1985 ; Knight et al. 1996 ). “ In viviparous species
however, the egg capsule is considerably thinner and, in sharks, often remains intact
around developing embryos throughout the course of development in utero,”
(Heiden et al. 2005 ; see also Hamlett and Koob 1999 ). Egg capsules of selachians
are diverse in their forms and can include tendrils, ribs, and ridges. The egg capsules
of sharks are generally rectangular in shape with the corners prolonged into anterior
and posterior pairs of horns. However, considerable variation exists in shape and
size in the different species (Krishnan 1959 ) (Figs. 12.1 and 12.2 ).
As reviewed by Heiden et al. ( 2005 ), “many skate egg capsules have adhesive
fi bers that moor the capsules to the sea fl oor, or some other substrate. This protects
© Springer Science+Business Media Dordrecht 2015
H. Ehrlich, Biological Materials of Marine Origin, Biologically- Inspired Systems 4,
DOI 10.1007/978-94-007-5730-1_12
Chapter 12
Egg-Capsule Proteins of Selachians
Abstract Egg capsules of sharks, skates and chimaerods are made of very specifi c
collagen and polyphenol-based fi brillar structures, which exhibit unusual preservation
even when fossilized. The dogfi sh egg capsule is a composite material constructed
largely from collagen fi brils with a highly ordered, kinked molecular arrangement
set in a matrix containing spherical fi ller particles composed of hydrophobic protein. The capsule consists of collagenous three-dimensional very ordered open networks. This molecular construct is responsible not only for specifi c fi ltering
properties, but also for strength of the unique structured capsule. Both capsular collagen and polyphenol-based proteins possess high biomimetic potential.
The egg capsules of sharks and rays have been described previously by a number of
workers (Beard 1890 ; Widakowich 1906 ; Hussakof and Welker 1908 ; Clark 1922 ;
Hobson 1930 ; Whitley 1938 ; Nalini 1940 ; Brown 1955 ; Krishnan 1959 ). Also
attention has been paid to similar structures in Chimaeroids (Bessels 1869 ; Jaekel
1901 ; Gill 1905 ; Dean 1912 ; Brown 1946 ). The egg capsules of Elasmobranchii are
widely recognised as important in species identifi cation, and provide relevant information concerning their reproductive biology (Whitley 1939 ; Oddone et al. 2004 ).
According to the modern view, the “nidamental gland in contemporary elasmobranchs secretes a tertiary accessory envelope, called the egg capsule, around the
fertilized ova as they pass through the oviduct and into the uterus,” (Heiden et al.
2005 ). Except some rays, the encapsulation of fertilized eggs occurs in oviparous
and nearly all viviparous species (Hamlett and Koob 1999 ). Due to peculiar thickness, the egg capsules of oviparous species are exceptionally durable. The biological sense of these structures is to protect embryos during protracted development in
the marine environment (Hunt 1985 ; Knight et al. 1996 ). “ In viviparous species
however, the egg capsule is considerably thinner and, in sharks, often remains intact
around developing embryos throughout the course of development in utero,”
(Heiden et al. 2005 ; see also Hamlett and Koob 1999 ). Egg capsules of selachians
are diverse in their forms and can include tendrils, ribs, and ridges. The egg capsules
of sharks are generally rectangular in shape with the corners prolonged into anterior
and posterior pairs of horns. However, considerable variation exists in shape and
size in the different species (Krishnan 1959 ) (Figs. 12.1 and 12.2 ).
As reviewed by Heiden et al. ( 2005 ), “many skate egg capsules have adhesive
fi bers that moor the capsules to the sea fl oor, or some other substrate. This protects