40
The Chondrichthyes (comprising the sharks, rays and chimaeras) are characterised by
a skeleton that is entirely cartilaginous, but more or less hardened by calcification. In this
group fertilisation is internal and accomplished by means of the paired intromittent
organs at the inner edge of the pelvic fins of males. These organs, misnamed "claspers",
are actually used to transfer sperm into the oviducts of the female during copulation.
Although a few elasmobranchs have adapted to life in fresh water, the chondrichthyans
are primarily marine fishes. They have developed an unusual solution to the osmotic
problems of life in the sea. By keeping a high concentration of urea in their blood and
other tissues, the chondrichthyans are able to maintain the ionic balance of their tissues
relative to seawater. After death, the urea is soon broken down to ammonia, which may
give the shark flesh an unpleasant smell or taste. Soaking the flesh in a 50% solution of
water and vinegar for an hour before cooking will remove all traces of urea and ammonia.
Most chondrichthyans are good eating, but the flesh is usually somewhat dry (like the
white meat of tuna fishes) and should be cooked accordingly. Any chondrichthyan
destined for the table should be thoroughly bled immediately after death and kept on ice
or frozen until it is to be cooked.
Two subclasses: Elasmobranchii (sharks and rays), with the upper jaw not fused to the
skull, teeth usually separate, and 5-7 pairs of gill openings; and Holocephali (chimaeras),
with the upper jaw fused to the skull, teeth represented by solid dental plates, and only
one pair of external gill openings.
nictitating
membrane
front margin
Topography of a shark
internostril
distance
total length
nasalftap
Ventral view of head
second
dorsal
fin
lower ti p
fold
The Chondrichthyes (comprising the sharks, rays and chimaeras) are characterised by
a skeleton that is entirely cartilaginous, but more or less hardened by calcification. In this
group fertilisation is internal and accomplished by means of the paired intromittent
organs at the inner edge of the pelvic fins of males. These organs, misnamed "claspers",
are actually used to transfer sperm into the oviducts of the female during copulation.
Although a few elasmobranchs have adapted to life in fresh water, the chondrichthyans
are primarily marine fishes. They have developed an unusual solution to the osmotic
problems of life in the sea. By keeping a high concentration of urea in their blood and
other tissues, the chondrichthyans are able to maintain the ionic balance of their tissues
relative to seawater. After death, the urea is soon broken down to ammonia, which may
give the shark flesh an unpleasant smell or taste. Soaking the flesh in a 50% solution of
water and vinegar for an hour before cooking will remove all traces of urea and ammonia.
Most chondrichthyans are good eating, but the flesh is usually somewhat dry (like the
white meat of tuna fishes) and should be cooked accordingly. Any chondrichthyan
destined for the table should be thoroughly bled immediately after death and kept on ice
or frozen until it is to be cooked.
Two subclasses: Elasmobranchii (sharks and rays), with the upper jaw not fused to the
skull, teeth usually separate, and 5-7 pairs of gill openings; and Holocephali (chimaeras),
with the upper jaw fused to the skull, teeth represented by solid dental plates, and only
one pair of external gill openings.
nictitating
membrane
front margin
Topography of a shark
internostril
distance
total length
nasalftap
Ventral view of head
second
dorsal
fin
lower ti p
fold