108
Investigations using histological techniques and SEM show that Type II odontodes
are associated with special epithelial structures to form a putative mechanosensory
organ. It was observed that the odontode base is localized deep in the fi sh dermis.
It was suggested that the “ presence of odontodes on the fi n spines and in the skin of
the head, lips, and barbels may enhance skin surface adhesion in torrential currents, ”
(Schaefer and Buitrago-Suárez 2002 ).
3.2.2 Keratinized Teeth
Lampreys are jawless, armorless fi sh without paired appendages. However, their
mouth is rigid, conical, and lined with keratinized teeth-like structures. The sucker
with 11 or 12 rows of these teeth, arranged in concentric circles and enclosed by an
oral hood, is the most distinguishing external features of the adult sea lamprey
( Petromyzon marinus). Teeth are cyclically replaced by the formation of new
teeth from the germinal epithelium, so that in a random sampling, 1 or 2 generations
of teeth may be observed (Alibardi and Segalla 2011 ). So called buccal funnel or
suctorial disk is the characteristic teeth-hood arrangement of the animal. The
lamprey fastens itself to various substrates and objects using this sucker. The buccal
funnel is surrounded by tiny fi nger-like papillae. Just posterior (interiorly) to the
mouth is the buccal cavity. At the back of the buccal cavity is a rasping tongue, used
for rasping the fl esh of a host. The tongue can be extended forward into the buccal
funnel to scrape fl esh. A valve called the velum separates the digestive tract from the
respiratory pathway. This prevents food from entering the gills, but keeps water
fl owing over the gills even while feeding (Iwasaki 2002 ). The tips of the teeth are
markedly sharp, and curves inward in the mouth.
Here, I take the liberty to insert the description of the fi ne structure of the
horny teeth of the lamprey, Entosphenus japonicas , made by Uehara et al. ( 1983 ) as
following:
“ Most of the horny teeth consisted of two horny and two nonhorny layers.
The primary horny layer was coated with keratin, and the cells were closely
packed and intensely interdigitated, joined together by many modifi ed desmosomes. The plasma membrane of the horny cell, unlike the membranes of other
vertebrates, was not thickened. The intercellular spaces were fi lled with electron-dense
material. Microridges were seen on the free surface. Structures resembling
microridges were found on the underside of the primary horny layer. The secondary
horny layer displayed various stages of keratinization. The keratinization
started at the apex and developed toward the base. In the early stage of keratinization, the superfi cial cells became cylindrical and were arranged in a row,
forming a dome-shaped line. Their nuclei were situated in the basal part of the
cells. The appearance of the nonhorny layers varied according to the degree of
keratinization of the horny layers beneath them. The nonhorny cells were joined
together by many desmosomes and possessed many tonofi lament bundles, ”
(Uehara et al. 1983 ).
3 Biocomposites and Mineralized Tissues
Investigations using histological techniques and SEM show that Type II odontodes
are associated with special epithelial structures to form a putative mechanosensory
organ. It was observed that the odontode base is localized deep in the fi sh dermis.
It was suggested that the “ presence of odontodes on the fi n spines and in the skin of
the head, lips, and barbels may enhance skin surface adhesion in torrential currents, ”
(Schaefer and Buitrago-Suárez 2002 ).
3.2.2 Keratinized Teeth
Lampreys are jawless, armorless fi sh without paired appendages. However, their
mouth is rigid, conical, and lined with keratinized teeth-like structures. The sucker
with 11 or 12 rows of these teeth, arranged in concentric circles and enclosed by an
oral hood, is the most distinguishing external features of the adult sea lamprey
( Petromyzon marinus). Teeth are cyclically replaced by the formation of new
teeth from the germinal epithelium, so that in a random sampling, 1 or 2 generations
of teeth may be observed (Alibardi and Segalla 2011 ). So called buccal funnel or
suctorial disk is the characteristic teeth-hood arrangement of the animal. The
lamprey fastens itself to various substrates and objects using this sucker. The buccal
funnel is surrounded by tiny fi nger-like papillae. Just posterior (interiorly) to the
mouth is the buccal cavity. At the back of the buccal cavity is a rasping tongue, used
for rasping the fl esh of a host. The tongue can be extended forward into the buccal
funnel to scrape fl esh. A valve called the velum separates the digestive tract from the
respiratory pathway. This prevents food from entering the gills, but keeps water
fl owing over the gills even while feeding (Iwasaki 2002 ). The tips of the teeth are
markedly sharp, and curves inward in the mouth.
Here, I take the liberty to insert the description of the fi ne structure of the
horny teeth of the lamprey, Entosphenus japonicas , made by Uehara et al. ( 1983 ) as
following:
“ Most of the horny teeth consisted of two horny and two nonhorny layers.
The primary horny layer was coated with keratin, and the cells were closely
packed and intensely interdigitated, joined together by many modifi ed desmosomes. The plasma membrane of the horny cell, unlike the membranes of other
vertebrates, was not thickened. The intercellular spaces were fi lled with electron-dense
material. Microridges were seen on the free surface. Structures resembling
microridges were found on the underside of the primary horny layer. The secondary
horny layer displayed various stages of keratinization. The keratinization
started at the apex and developed toward the base. In the early stage of keratinization, the superfi cial cells became cylindrical and were arranged in a row,
forming a dome-shaped line. Their nuclei were situated in the basal part of the
cells. The appearance of the nonhorny layers varied according to the degree of
keratinization of the horny layers beneath them. The nonhorny cells were joined
together by many desmosomes and possessed many tonofi lament bundles, ”
(Uehara et al. 1983 ).
3 Biocomposites and Mineralized Tissues