7
concretion. Because the similarity to modern hagfi shes is striking, it was suggested
that little evolutionary change in Myxini has been over the last 300 million years.
According to modern point of view (Kuratani and Ota 2008 ), these animals are
unique among living chordates. For example, they have a partial skull, but no vertebrae, and so they are not truly vertebrates. The skeleton lacks bone and is composed
of cartilage. Hagfi sh are almost blind, have no cerebrum or cerebellum, no jaws or
stomach, but three accessory hearts. They have four pairs of sensing tentacles
arranged around their mouth and also have well developed senses of touch and
smell. Interestingly, they can “sneeze” when their nostrils clog with their own slime.
Being jawless, a hagfi sh is equipped with two pairs of tooth-like structures, the
rasps, which are located on the top of a tongue-like projection. The pairs of rasps
pinch together after this tongue is pulled back into the hagfi sh’s mouth. This bite is
used in catching and eating marine invertebrates like polychaete worms, or to tear
into the fl esh of dying and dead fi sh which have sunk to the muddy ocean bottom.
Principally, their metabolism is very slow, therefore hagfi sh may go for up to
7 months without eating any food. These vertebrates are slimy and capable of tying
their body into a knot. Furthermore, hagfi sh are known for producing large amounts
of slime when stressed (see also Sect. 11.2 in this work). The production of
the slime is believed to be some kind of defence mechanism against gill-breathing
predators. It was reported that the slime can reduce water fl ow over the gills of fi sh.
Slime thread skeins and mucin vesicles are two interacting components of hagfi sh
slime. Both are released from glands along the ventrolateral length of these primitive
vertebrates (see for review Downing et al. 1981 ; Lim et al. 2006 ).
Class Cephalaspidomorphi (Petromyzontida)
Lampreys or Hyperoartii are another group of primitive (Ruud 1954 ) and jawless
fi shes. Non- parasitic species are able to eat only in their larval form, dying as adults
soon after reproducing. Parasitic species, however, latching onto the bodies of freshwater fi sh (Renaud and Economidis 2010 ). Lampreys have no jaws but possess an
annular cartilage that supports the supraoral and infraoral laminae. Their body is
naked and elongated. They possess seven branchial openings (or pores) on either
side of the body. The seven pairs of gill pouches are supported by a surrounding
branchial basket consisting of an elaborate network of fused cartilaginous elements.
Lamprey cartilage is unique to the group and contains hydrophobic protein lamprin
(Robson et al. 2000 ). The teeth on the oral disc and tongue-like piston of the adult
lamprey are made of keratin (Fig. 1.1 ). They possess a hollow core allowing for a
number of replacement teeth to occur one on top of the other. It has been estimated
that over the course of 2 years, an adult Sea Lamprey, Petromyzon marinus , may
replace its teeth about 30 times (Renaud 2011 ). The skeleton contains no bone, only
cartilage, although this cartilage may be calcifi ed. The main axial support for the
body is the notochord, which is persistent throughout the life of the animal.
Rudimentary vertebral elements termed arcualia are arranged two per myomere on
either side along the dorsal nerve cord.
1.2 Part I: Biomaterials of Vertebrate Origin. An Overview
concretion. Because the similarity to modern hagfi shes is striking, it was suggested
that little evolutionary change in Myxini has been over the last 300 million years.
According to modern point of view (Kuratani and Ota 2008 ), these animals are
unique among living chordates. For example, they have a partial skull, but no vertebrae, and so they are not truly vertebrates. The skeleton lacks bone and is composed
of cartilage. Hagfi sh are almost blind, have no cerebrum or cerebellum, no jaws or
stomach, but three accessory hearts. They have four pairs of sensing tentacles
arranged around their mouth and also have well developed senses of touch and
smell. Interestingly, they can “sneeze” when their nostrils clog with their own slime.
Being jawless, a hagfi sh is equipped with two pairs of tooth-like structures, the
rasps, which are located on the top of a tongue-like projection. The pairs of rasps
pinch together after this tongue is pulled back into the hagfi sh’s mouth. This bite is
used in catching and eating marine invertebrates like polychaete worms, or to tear
into the fl esh of dying and dead fi sh which have sunk to the muddy ocean bottom.
Principally, their metabolism is very slow, therefore hagfi sh may go for up to
7 months without eating any food. These vertebrates are slimy and capable of tying
their body into a knot. Furthermore, hagfi sh are known for producing large amounts
of slime when stressed (see also Sect. 11.2 in this work). The production of
the slime is believed to be some kind of defence mechanism against gill-breathing
predators. It was reported that the slime can reduce water fl ow over the gills of fi sh.
Slime thread skeins and mucin vesicles are two interacting components of hagfi sh
slime. Both are released from glands along the ventrolateral length of these primitive
vertebrates (see for review Downing et al. 1981 ; Lim et al. 2006 ).
Class Cephalaspidomorphi (Petromyzontida)
Lampreys or Hyperoartii are another group of primitive (Ruud 1954 ) and jawless
fi shes. Non- parasitic species are able to eat only in their larval form, dying as adults
soon after reproducing. Parasitic species, however, latching onto the bodies of freshwater fi sh (Renaud and Economidis 2010 ). Lampreys have no jaws but possess an
annular cartilage that supports the supraoral and infraoral laminae. Their body is
naked and elongated. They possess seven branchial openings (or pores) on either
side of the body. The seven pairs of gill pouches are supported by a surrounding
branchial basket consisting of an elaborate network of fused cartilaginous elements.
Lamprey cartilage is unique to the group and contains hydrophobic protein lamprin
(Robson et al. 2000 ). The teeth on the oral disc and tongue-like piston of the adult
lamprey are made of keratin (Fig. 1.1 ). They possess a hollow core allowing for a
number of replacement teeth to occur one on top of the other. It has been estimated
that over the course of 2 years, an adult Sea Lamprey, Petromyzon marinus , may
replace its teeth about 30 times (Renaud 2011 ). The skeleton contains no bone, only
cartilage, although this cartilage may be calcifi ed. The main axial support for the
body is the notochord, which is persistent throughout the life of the animal.
Rudimentary vertebral elements termed arcualia are arranged two per myomere on
either side along the dorsal nerve cord.
1.2 Part I: Biomaterials of Vertebrate Origin. An Overview