lec2b skin and exoskeleton summer2014

8/18/2019 Lec2B Skin and Exoskeleton Summer2014

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Comparative Anatomy of The

Skin & Exoskeleton


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GENERAL FUNCTION OF THESKIN & EXOSKELETON

• Protection against – Dehydration/dessication – Foreign bodies – Extreme environmental condition – Predation

• Skin and Exoskeleton – Skin

• surface covering• separable from the underlying muscle layer

– Exoskeleton • external covering derived from the skin• Hardening processes in epidermis or dermis


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The Skin

• Occurs only in vertebrates• Lower chordates lack a skin

– Urochordates – one-layeredepidermis + ‘tunic’ secreted byepidermis

–

Amphioxus – one-layeredepidermis only

• Two general layers: – Epidermis

• Outer• Epithelial cells•

Derived from ectoderm – Dermis

• Inner• Connective tissue• Derived from the mesoderm


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Skin of Aquatic Vertebrates

• Cyclostomes, fishes,

tailed amphibians

• Thin epidermis

• Mucous gland cells- skin

moist and slimy

• Dermis – loose layer near epidermis – compact inner layer


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Skin of Land Vertebrates

• Keratinization

• Frog Skin – Epidermis

• Stratum corneum – outermost, thin, flattened keratinized

• Stratum germinativum – inner, columnar, actively dividing

– Dermis/ Corium• Stratum laxum – loose connective tissue

• Stratum compactum – dense, parallel wavy fibers

•

Contains: – pigment cells (Chromatophores)

– Cutaneous glands – mucous and other secretions

– Smooth muscles

– Blood vessels and nerves


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FROG SKIN

EPIDERMIS

MUCOUSGLAND


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Exoskeleton

• Derived from skinby hardeningprocesses in

epidermis or dermisor both

• Epidermal –special portions of

stratum corneum• Dermal – consists

of bone


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EXOSKELETON OF FISHES

• Scales – Dermal in origin

– Six types• Placoid

• Cosmoid

• Paleoniscoid

• Ganoid/

Lepidosteoid

• Cycloid

• Ctenoid


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PLACOID SCALES

• Found inelasmobranchs –shagreen (shark skin)

• Basal plate carrying a

projecting spine• “denticles” – consists of

dentine and structure isidentical with the dentineof teeth

• Spine contains a pulpcavity from whichdentinal tubules branch


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COSMOID SCALES

• Occurs in extinct fish ofthe groupsCrossopterygii and

Dipnoi• 3 layers:

– Cosmine – outer; similarto dentine but dentinal

tubules occur in clusters – Vascular bone – middle

– Lamellate bone - inner


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PALEONISCOID SCALES

• found in extinctpaleoniscids andPolypterus

• Intermediate betweencosmoid and typicalganoid scale – Upper layer – Ganoin

– Middle layer – Cosmine

– Lower layer – lamellatebone


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GANOID SCALES

• Found in Chondrostei and some Holostei (sturgeons, pikes, andallies)

• Lamellae of Ganoindeposited on a layer oflamellate bone

•

Hard, shiny, rhomboidplates – Lepidosteus

• Bony rhombic crestedplates - Acipenser


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CYCLOID SCALES

• Occur in modern fishes(some Holostei, Dipnoi,Teleostei)

• Thin, flexible, rounded

scales with concentricridges

• Set in pockets of skin inoverlapping row

•

Inner layer – fibrousconnective tissue• Outer layer - hard bony

layer


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CTENOID SCALE

• Occurs in about half of

Osteichthyes (most

teleosts)

•Similar to cycloid but thefree part is covered with

small teeth

• age and growth rate of fish

can be determined usingscales


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EXOSKELETON OF FISHES

• Dermal Fin Rays – Rods that support the fins

– Supported through ligamentous connections

with endoskeletal fin rays – 4 types (Goodrich, 1904)

• Ceratotrichia

• Actinotrichia

• Lepidotrichia

• Camptotrichia


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CERATOTRICHIA

• Slender,

flexible,

unjointed

• Keratinized

dermal rods

• Elasmobranchs


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ACTINOTRICHIA

• Occur only during development of bony fish

• Similar to ceratotrichia but is replaced by

lepidotrichia


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LEPIDOTRICHIA

• Branched, jointed

rays made up of

bone

• Characteristic of

Osteichthyes in

general


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CAMPTOTRICHIA

• Limited to present

Dipnoi

• Intermediatebetween

Ceratotrichia and

Lepidotrichia

• Dermal rays,scale-covered


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EXOSKELETON OF REPTILES

• With scales and scale-like areas of

epidermal origin

• Thickened areas of Stratum Corneum

• Continuous horny layer

• Some also have dermal bony plates

beneath epidermal scales

• Epidermal thickenings – scales or scutes

• Dermal thickenings - plates


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EXOSKELETONS OF SQUAMATES AND

CROCODILES

• Scales on both dorsal and ventral portions

• Bony plates under the scales in some


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EXOSKELETON OF TURTLES

• Scales in the head, limbs and tail

• Entire body protected by the CARAPACE

AND PLASTRON

• Horny beaks

• Claws


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CARAPACE scutes

• (outer, dorsalside)

• 1 nuchal scute• 5 neural/vertebral

scutes• 4 pairs costal/

pleural scutes• Marginal scutes

• 1 pair pygalscutes


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CARAPACE plates

• Inner, ventral side

• 1 nuchal plate

• 8 neural/vertebralplates

• 8 pairs costal/pleuralplates

• Marginal plates

• 1 pair precaudal

plates• 1 pygal plate


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PLASTRON scutes

• Outer,

ventral

side


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PLASTRON

• Inner, dorsal side

• Epiplastron (paired)

• Entoplastron (median)

• Hyoplastron (paired)• Hypoplastron (paired)

• Xiphiplastron (paired)


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EXOSKELETON OF BIRDS

• Clothed with

feathers

• Scales and claws on

the feet

• Horny beaks

• Lacks dermal

exoskeleton


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FEATHERS

• Contour feathers – Remiges (wings)

– Rectrices (tail/ anal part)

– Coverts (body covering)

• Down feathers or plumule – fluffy covering,

in between the bases of contour feathers

• Hair feathers or filoplume – hairs visiblefrom a plucked bird


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CONTOUR FEATHER PARTS

• Quill (Central axis)• Inferior and Superior

umbilicus• Vane (web-like expansion)

– outer and inner• Calamus (lower part of

quill)• Shaft or rachis (part of quill

that supports the vane)•

Umbilical groove• Barbs and barbules


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CONTOUR FEATHER PARTS

• Quill (Central axis)• Inferior and Superior

umbilicus• Vane (web-like expansion)

– outer and inner• Calamus (lower part of

quill)• Shaft or rachis (part of quill

that supports the vane)•

Umbilical groove• Barbs and barbules


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DOWN FEATHER PARTS

• Short quill

• Barbs – soft rays

• Barbules –

minute side rays


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FILOPLUME

• Consists of a main axis with few terminal

barbs


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FEATHER TRACTS

• Pterylae- areas of skin which bear feathers• Apterylae – featherless tracts


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EXOSKELETON OF MAMMALS

• Hair

• Scales

• Claws, Nails, Hooves and Horns –

compressed layers of stratum corneum


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HAIR OF MAMMALS

• Found in no othervertebrates

• Types: – Facial vibrissae – Bristles/ spine-like hairs –

spiny anteaters – Guard hairs – fur – Aristate hairs – smaller and

fairly numerous – Wool – fine, short, wavy

• Parts: –

Hair follicles – Shaft – Root – Cuticle – Medulla – Cortex


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SCALES OF MAMMALS

• Epidermal, horny

(keratinized), usually

interspersed with

scanty hair – Tails of rats, mice or

beavers

– Scaly anteaters

•

Epidermal scutes anddermal scales

– armadillos


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CLAWS

•

Curved horny sheath covering the last joint of thedigit and enclose terminal skeletal joint

• Ventral side – sole

• Compressed layer of stratum corneum – compact

horn


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NAILS

• Reduced sole


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HOOVES

• Enlarged and thickened sole

• Present in ungulates


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HORNS

• True horns – Hollow,

epidermal in

origin – Covers hollow

bony cores

– Cattle, sheep,

goats, antelopes – Occur in both

sexes

– Never shed


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ANTLERS

• “False Horns”

• Family Cervidae (deerfamily)

• Solid bony outgrowths ofthe frontal bone

• Limited to males

•

Shed annually


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TODAY’S TASK

• DRAW THE FF. SPECIMENS:

–1. Placoid, Ganoid, Cycloid, Ctenoid Scales –2. Carapace (label the parts) –3. Plastron (label the parts) –4. Types of feathers (label the parts) -5. Horns and Antlers

lec2b skin and exoskeleton summer2014

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