scales

1. SCALES OF FISHES AND
REPTILES BY ANGATRA MANDAL
SEM-III
ZOOLOGY
DURGAPUR GOVT
COLLEGE

2. What are Scales?
 The term Scale derives from the Old French escale, meaning a shell
pod or husk.
 Scales are actually small plate or shield forming part of the outer skin
layers of certain animals
 Scales provide protection to the body from any outside dangers of
the environment like predators and infections.

3. Who have Scales ?
 Mainly the class PISCES and class REPTILIA possesses scales on their
body.
 But other than them also Avian scales, Mammalian Sales and
Arthropod Scales are observed due to the fact of evolution for
protection against environment.
 Here after in our presentation we will discuss about scales of Fishes
and Reptiles.

4. Scales of Fishes and their Types
 Fish scales are part of the Fish’s integumentary system.
 Produced from the Mesoderm layer of the Dermis, which
distinguishes them from Reptile Scale.
 Scales can vary enormously in size, shape, structure and Extent.
 There are four main kinds of scales and numerous variations of each
kind.
(i) Placoid (sharks and rays)
(ii) Cosmoid (lungfishes and some fossil fishes)
(iii) Ganoid (bichirs , Bowfin, paddlefishes, gars, sturgeons)
(iv) Cycloid and Ctenoid (most bony fishes)

5. Placoid Scales
 Placoid scales are found in sharks and rays, and can vary greatly in external appearance.
 Unlike the scales of bony fishes, placoid scales dont increase in size as the fish grows,
instead new scales are added between older scales. Placoid scales are often referred to
as denticles.
 Each placoid scale consists of a flattened rectangular base plate which is embedded in
the fish, and variously developed structures, such as spines, which project posteriorly on
the surface. The spines give many species a rough texture. There are large differences in
the development of these spines between different species.
 Placoid scales are composed of a vascular (supplied with blood) inner core of pulp, a
middle layer of dentine and a hard enamel-like outer layer of vitrodentine.

6. Cosmoid Scale
 Cosmoid scales are found in the Lungfishes (family Ceratodidae) and
some fossil fishes.
 Cosmoid scales are similar to placoid scales and probably evolved
from the fusion of placoid scales. They consist of two basal layers of
bone, a layer of dentine-like cosmine, and an outer layer of
vitrodentine.
 As the fish grows each scale becomes larger as new bone is added to
the basal layers.

7. Ganoid Scales
 Ganoid scales (or modified ganoid scales) are found in fishes such as the
bichirs (Polypteridae), Bowfin (Amia calva), paddlefishes (Polyodontidae),
gars (Lepisosteidae), and sturgeons (Acipenseridae).
 Ganoid scales are usually rhomboid in shape and have articulating peg and
socket joints between them. They are modified cosmoid scales which consist
of a bony basal layer, a layer of dentine, and an outer layer of ganoine (an
inorganic bone salt).
 Ganoid scales are also known from some fossil paleoniscoid fishes.

8. Cycloid and Ctenoid Scales
 Cycloid and ctenoid scales are found in the majority of bony fishes (the Teleostei).
 The 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.
 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.
 Cycloid and ctenoid scales consist of two main regions, a surface 'bony' layer,
composed of an organic framework impregnated largely with calcium based salts, and
a deeper fibrous layer composed mainly of collagen.
 Cycloid and ctenoid scales are derived from ganoid scales that have lost the ganoine
and thinned the bony embedded plate.
 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, which look a little like the growth
rings in the trunk of a tree. These are sometimes used to determine the age of the fish.
Ctenoid Scale
Cycloid Scale

9. Scales of Reptiles and their types
 Reptile skin is covered with scutes or scales which, along with many other
characteristics, distinguish reptiles from animals of other classes. They are
made of alpha and beta-keratin and are formed from the epidermis.
 The scales of all reptiles have an epidermal component, but many reptiles,
such as crocodilians and turtles, have osteoderms underlying the epidermal
scale. Such scales are more properly termed scutes. Snakes, tuataras and
many lizards lack osteoderms.
 Reptile scale types include cycloid, granular (which appear bumpy), and
keeled (which have a center ridge).

10. Diff. b/w scales of fish and reptile
 Produced from the Mesoderm
layer of the Dermis
 They are made of a surface layer
containing hydroxyapatite,
calcium carbonate and a deeper
layer mostly made of collagen
type I
 They are made of alpha and beta-
keratin and are formed from the
epidermis
 They are made of Keratin
Scales of Fish Scales of Reptiles

11. ThAnK_yOu