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Unit 18: Biology Part 1 Page 23 of 60
these fish do belong to the skates, and the second group is
vertebrate subphylum, they do not the chimaera, sometimes called the
technically have vertebrae. ghost sharks.
In fact, this group of fish is so These two groups share many
different than fish with jaws, it has things in common, including the
led some scientists to wonder if presence of jaws, paired fins, a
they should be called “fish” at all. two-chambered heart, and bodies
Along with their lack of jaws, the made of cartilage.
jawless fish are notably different As mentioned before, cartilage is
than other fish because they do not the same material that makes up
have paired fins. the outside of your ears and nose.
Agnatha do not have an identifiable One of the challenges of having
stomach, and don’t have a true bodies made of cartilage instead of
eye, instead having a light- having bones is that the
sensitive eye-like structure. These cartilaginous fishes have no bone
fish have bodies made of cartilage marrow in which to produce red
and have a heart with only two blood cells. These cells are needed
chambers as opposed to the to carry oxygen around the body,
normal four. so the cartilaginous fishes produce
them in other locations, including
the spleen, around the gonads, and
in a special organ called Leydig’s
Organ, found only in this group.
Additionally, the cartilaginous
fishes have dermal teeth, also
known as placoid scales. These
Hagfish also produce a slimy scales give the bodies of the
substance which has led some cartilaginous fishes a rough,
people to call them “slime eels,” sandpaper-like feel.
although they are not eels at all. This white fin
The Pacific Hagfish is one example shark, like all
of a jawless fish. sharks, have
The cartilaginous fishes are a bodies made of
group of about 1,000 species cartilage rather
separated into two groups. The than bone.
first group is the sharks, rays, and
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