Biology Reference
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feeding and/or the use of adult oral disc for attachment. The pharynx of
larva serves as a conduit for materials entering the oral aperture on their
way to the oesophagus, whereas in adults the oral aperture is connected
to an oesophagus lying above the pharynx and uniting with the intestine
near the cardiac region (Fig. 11). This separate oesophagus permits for tidal
ventilation in and out of the branchiopores if the suctorial disc is attached
to some surface. The features of expansion of the cartilaginous branchial
basket during metamorphosis has been referenced above. Transformation
of the gill epithelium also takes place during metamorphosis with the
appearance of adult-type, mitochondria-rich (formerly called chloride) cells
that become fully mature in morphology by stage 6 or 7 (Peek and Youson,
1979a,1979b). There have numerous recent studies on the appearance
of lamprey gill epithelium in larva and adults (for example, see Bartels
et al . , 2009) but one study with direct attention on the gill epithelium in
metamorphosis is important to highlight (Reis-Santos et al . , 2008). This
latter study measured the expression of key ion-transporting proteins
(Na + /K + -ATPase, vacuolar [V]-type H + -ATPase, and carbonic anhydrase
[CA]) in the examination of osmoregulatory differences between larval
and metamorphosing P. marinus . Immunoreactivity for these proteins was
also studied. As might be expected, larva did not survive even 10 ° °° sea
water but survival in 25-35 ° °° increased as metamorphosis progresses into
later stages. Branchial Na + /K + -ATPase was 10X higher in metamorphosing
animals over larvae, irrespective of salinity, and corresponded to intense
immunoreactivity to antiserum to this protein in cells in the interlamellar
spaces during metamorphosis, i.e., in developing mitochondria-rich cells.
Conversely, H + -ATPase had a negative correlation with salinity and the
immunohistochemistry indicated that this protein is not localized in the
Na + /K + -ATPase-immunoreactive cells. There seems to be a correlation
between the increase in salinity tolerance of metamorphosing lampreys
with the expression of Na + /K + -ATPase but H + -ATPase is downregulated
by changes in salinity (Reis-Santos et al . , 2008).
2.8.1.8 Blood and iron metabolism
Over the past twenty years there has been a fl urry of interest in iron
metabolism in lampreys due to the deposits of this metal in many tissues and
organs at levels that would be considered intolerable in other vertebrates
(Morgan, 1980). Although iron concentrations in the blood and tissues
of lampreys vary between species and even may vary within different
populations of the same species (Holmes and Youson, 1996), there seems
to be a shift in the distribution of iron during metamorphosis (Fig. 15). It
is beyond the scope of the present chapter to deal with all of the details
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