cose and sulphate in the approximate ratio 1: 1,
but details of the structure are otherwise not
known [123]. Glycan sulphates with obvious
species-specific differences are found in the slime
secretions of the molluscs. Whereas the properties of vertebrate mucus are determined by glycoproteins, in the molluscs the nature of the proteo glycan components is the decisive factor. As in
other prosobranchs, the hypobranchial gland in
the gill cavity of the Japanese species Charonia
lampas produces a slime which binds foreign matter present in the respiratory water stream. This
secretion was found to contain charonin sulphate,
which is a mixture of glucan sulphates of varying
sulphate content; the high-sulphate variety are
~(1-4) linked, like cellulose, whereas the lowsulphate type have a(1-4) and a(1-6) bonds, as
in glycogen. The hypobranchial gland of the common whelk Buccinum undatum also secretes a
~(1-4) glucan sulphate in addition to a glycoprotein. On the other hand, the hypobranchial
mucus of Busycon canaliculatum, whose odontophore contains glucan sulphate (as mentioned),
has a sulphated glycan with galactose and glucosamine components. Even more complex sulphated polysaccharides built up of various hexosamines and hexoses have been found in the
hypobranchial-gland secretions of Neptunea lactea and in the epidermal slime of the pulmonate
slug Agriolimax columbianus. The mucopolysaccharide of the pulmonate snail Otala lactea actually contains uronic acid. In contrast, a simple
glucan sulphate is again found in the mantle slime
of the scallop Pecten maximus [123].
The eggs of many aquatic invertebrates are
enveloped in a gelatinous membrane, the properties of which are often determined by the presence of mucopolysaccharides. Species-specific
glycan sulphates have been found in the egg
membranes of various sea urchins; these are
referred to as fertllisins because of their probable
involvement in sperm agglutination and fertilization. They mostly include fucose sulphates, which
may be branched and in some species may also
contain other hexoses as subcomponents. Other
species have galactan sulphates, and at least in
Echinus esculentus the galactose has predominantly the L- configuration. Finally, the egg jelly of
the sand dollar Echinarachnius parma contains a
fructosan sulphate. The only starfish to be investigated was found to contain a hetero-glycan
sulphate with the components glucose, fucose
and mannose [123].
Simple glycan sulphates have also been found
in other animal groups, e.g. fucan sulphate in the
13.4.3 Chitin and Cellulose
485
skin of the holothurians or galactan sulphate in
the mussels. More complex glycan sulphates with
an even wider distribution contain various hexoses and hexosamines but no uronic acids. These
include the horatin sulphate of the hepatopancreas in the snail Charonia lampas; polysaccharides from mussels (spisulan), the oligochaetes
Lumbricus and Tubifex, and various ascidians;
and lingulan from the stem of the brachiopod
Lingula [120, 123, 208, 265]. Glycoproteins containing aminoethylphosphonic acid (AEPn) were
discovered in the slime of sea anemones such as
Metridium senile and M. dianthus. This sticky
mucus is secreted by the ectodermal cells and serves mainly to trap plankton. It contains none of
the typical acidic mucopolysaccharides but has
glycoproteins with 20-30 % carbohydrate and
10-15 % AEPn ester-bound to the carbohydrate
[39].
Glycan phosphates are seldom found in animals. One example of this class of substances is
the acidic polysaccharide found in the tube of the
polychaete Hyalinoecia (previously Onuphis)
tubicola; this is composed of only glucose and
phosphate and is known as onuphinic acid. The
exact structure is not known but the sugar residues appear to have ~(1-3) bonds and carry
monophosphates in position 4 or 6. A phosphaterich polysaccharide of mannose, glucose and
xylose has been reported in the tube of the polychaete Chaetopterus variopedatus [123].
13.4.3 Chitin and Cellulose
The term chitin is used both for native proteoglycans and for derived polysaccharides. Chitin is
widely distributed in fungi and animals; with an
estimated annual production of 1010_1011 t, it
competes with cellulose for the position of the
most abundant organic substance in the biosphere. In fungi, chitin is associated with other
polysaccharides, whereas in animals it is probably
exclusively bound to protein. The most wellknown example of chitin in animals is the external and internal skeleton of the arthropods in
which chitin also lines the anterior and posterior
gut. In the annelids, chitin is found in the bristles,
mouthparts and gut lining; in the molluscs it is
present, for example, in the organic matrix of the
shell and the radula; and in the cephalopods, it is
also found in the cuttlebone, the suckers and the
lining of the anterior gut. Examples of chitincontaining structures are the shells of the brachiopods; the outer skeleton of the bryozoans; the
but details of the structure are otherwise not
known [123]. Glycan sulphates with obvious
species-specific differences are found in the slime
secretions of the molluscs. Whereas the properties of vertebrate mucus are determined by glycoproteins, in the molluscs the nature of the proteo glycan components is the decisive factor. As in
other prosobranchs, the hypobranchial gland in
the gill cavity of the Japanese species Charonia
lampas produces a slime which binds foreign matter present in the respiratory water stream. This
secretion was found to contain charonin sulphate,
which is a mixture of glucan sulphates of varying
sulphate content; the high-sulphate variety are
~(1-4) linked, like cellulose, whereas the lowsulphate type have a(1-4) and a(1-6) bonds, as
in glycogen. The hypobranchial gland of the common whelk Buccinum undatum also secretes a
~(1-4) glucan sulphate in addition to a glycoprotein. On the other hand, the hypobranchial
mucus of Busycon canaliculatum, whose odontophore contains glucan sulphate (as mentioned),
has a sulphated glycan with galactose and glucosamine components. Even more complex sulphated polysaccharides built up of various hexosamines and hexoses have been found in the
hypobranchial-gland secretions of Neptunea lactea and in the epidermal slime of the pulmonate
slug Agriolimax columbianus. The mucopolysaccharide of the pulmonate snail Otala lactea actually contains uronic acid. In contrast, a simple
glucan sulphate is again found in the mantle slime
of the scallop Pecten maximus [123].
The eggs of many aquatic invertebrates are
enveloped in a gelatinous membrane, the properties of which are often determined by the presence of mucopolysaccharides. Species-specific
glycan sulphates have been found in the egg
membranes of various sea urchins; these are
referred to as fertllisins because of their probable
involvement in sperm agglutination and fertilization. They mostly include fucose sulphates, which
may be branched and in some species may also
contain other hexoses as subcomponents. Other
species have galactan sulphates, and at least in
Echinus esculentus the galactose has predominantly the L- configuration. Finally, the egg jelly of
the sand dollar Echinarachnius parma contains a
fructosan sulphate. The only starfish to be investigated was found to contain a hetero-glycan
sulphate with the components glucose, fucose
and mannose [123].
Simple glycan sulphates have also been found
in other animal groups, e.g. fucan sulphate in the
13.4.3 Chitin and Cellulose
485
skin of the holothurians or galactan sulphate in
the mussels. More complex glycan sulphates with
an even wider distribution contain various hexoses and hexosamines but no uronic acids. These
include the horatin sulphate of the hepatopancreas in the snail Charonia lampas; polysaccharides from mussels (spisulan), the oligochaetes
Lumbricus and Tubifex, and various ascidians;
and lingulan from the stem of the brachiopod
Lingula [120, 123, 208, 265]. Glycoproteins containing aminoethylphosphonic acid (AEPn) were
discovered in the slime of sea anemones such as
Metridium senile and M. dianthus. This sticky
mucus is secreted by the ectodermal cells and serves mainly to trap plankton. It contains none of
the typical acidic mucopolysaccharides but has
glycoproteins with 20-30 % carbohydrate and
10-15 % AEPn ester-bound to the carbohydrate
[39].
Glycan phosphates are seldom found in animals. One example of this class of substances is
the acidic polysaccharide found in the tube of the
polychaete Hyalinoecia (previously Onuphis)
tubicola; this is composed of only glucose and
phosphate and is known as onuphinic acid. The
exact structure is not known but the sugar residues appear to have ~(1-3) bonds and carry
monophosphates in position 4 or 6. A phosphaterich polysaccharide of mannose, glucose and
xylose has been reported in the tube of the polychaete Chaetopterus variopedatus [123].
13.4.3 Chitin and Cellulose
The term chitin is used both for native proteoglycans and for derived polysaccharides. Chitin is
widely distributed in fungi and animals; with an
estimated annual production of 1010_1011 t, it
competes with cellulose for the position of the
most abundant organic substance in the biosphere. In fungi, chitin is associated with other
polysaccharides, whereas in animals it is probably
exclusively bound to protein. The most wellknown example of chitin in animals is the external and internal skeleton of the arthropods in
which chitin also lines the anterior and posterior
gut. In the annelids, chitin is found in the bristles,
mouthparts and gut lining; in the molluscs it is
present, for example, in the organic matrix of the
shell and the radula; and in the cephalopods, it is
also found in the cuttlebone, the suckers and the
lining of the anterior gut. Examples of chitincontaining structures are the shells of the brachiopods; the outer skeleton of the bryozoans; the