2.  Scales are overlapping series of hard plates
that cover a fish’s body
 Scales serve to protect the body from the
outside dangers such as predators and
infection.

3.  Present on palezoic sharks, and are still present on today’s sharks,
skates and rays
 Often referred as denticles
 They do not increase in size as the fish grows (new scales are
added).

4.  Flattened rectangular base plate which is embedded on the fish,
spines which project posteriorly on the surface.
 It is composed of a vascular inner core of pulp, a middle layer of
dentin and a hard enamel-like outer layer of vitrodentine.

5.  The function of these scales is for
protection against predators, although in
some sharks, they may also have a
hydrodynamic function.
 help the shark swim more quickly because
their streamlined shapes helps decrease the
friction of the water flowing along the shark's
body

7.  found in the majority of bony fishes (the Teleostei) and
modern lobe finned fishes.
 Ctenoid scales have a variously developed spiny posterior
margin (the word 'ctenoid' comes from the Greek cteno,
meaning comb, and refers to the comb-like ctenii on the
margin of the scale).
 Cycloid scales have a smooth posterior margin lacking ctenii.
The word 'cycloid' comes from the Greek cyclo, meaning
circle.

8.  anterior part of each scale is usually overlapped by
the posterior portion of the scale in front.
◦ This arrangement of imbricate (overlapping)
scales gives the fish greater flexibility than in
those species with cosmoid and ganoid scales.

9.  crenate, with simple indentations in the
margin, spinoid, with developed spines that
are continuous with the main body of the
scale, and ctenoid, in which the ctenii are
formed as separate bony growths which are
distinct from the main body of the scale.

10.  As a fish with cycloid or ctenoid scales grows, its scales also
grow. This results in a pattern of concentric growth rings on
the scale.
◦ These are sometimes used to determine the age of the fish.
◦ thin, large, round or oval,

11.  Protection and Hydrodynamics