INVERTEBRATE BODY COVERING
Protozoan body covering
· Plasma membrane acts as the body covering.
· Some have an additional gelatinous outer layer.
· Some have a complex body covering called Pellicle. Ex:- Paramecium
Pellicle
· Two membranes are present as outer alveolar membrane and outer alveolar membrane.
· Between those two an alveolar cavity is present.
· Some have cilia in the pellicle.
Poriferan body covering
· Thin.
· Two types of epidermis.
- Pinacoderm: outer epidermis. Single layer of Pinacocytes. Pinacocytes are scale like falttened cells.
- Choanoderm: inner epidermis. Single layer of choanocytes. Choanocytes are oval shaped cells with a flagellum on each.
· Between those to lies the mesoglea or mesenchyma.
· It’s a jelly like layer consist of spicules and amoebocytes, enclosing a central cavity called spongocoel.
· Spicules supply strength and amoebocytes give rise to new cells.
· Ostia are located on the wall.
Cnidarian body covering
· Similar to that of Poriferan.
· Outer epidermis: Cuticle is present.
Consist of small cubicle cells.
· Inner gastrodermis: Mainly consist of columnar epithelial cells.
· Mesoglea: Jelly like layer.
Platyhelminthes, nematode, annelid and arthropod body covering.
· Single layer epidermis is present.
· Cuticle is present on the epidermis.
· Some arthropods have an inner layer of dermis.
VERTEBRATE BODY COVERING
· Body covering is called as skin.
· It has a multilayered structure.
· Consist of two layers as epidermis and dermis.
Epidermis
· Multilayered.
· Avascular.
· Forms structures such as feathers, claws, scales…etc.
· From top to bottom of the epidermis;
- Stratum corneum: Dead keratinized cells are on the surface.
- Stratum germinativum
- Basal lamina.
Dermis
· Fibrous connective tissue with blood vessels, nerves and sensory receptors.
· Fish scales are derived from the dermis.
Fish skin
· Relatively thin.
· Derivatives of the skin;
- Scales: Bony scales derived from dermis.
Bone cells come into the dermis and secrete scales. Afterwards they leave. Dentine and enamel layers are later deposited on those scales.
- Melanophores: Star shaped cells that lie under the epidermis.
- Glands
I. Mucous glands: unicellular mucous producing glands. Mucous reduce friction when swimming. Produce mucous cocoon to protect from predators and heat in dry seasons. Also prevent invasion of bacteria.
II. Poison glands: produce poisonous substances.
III. Light emitting glands: aids to attraction, species recognition and avoid predators.
Amphibian skin
· Thin, moist skin.
· Can breathe through the skin.
· Derivatives of the skin
- Glands
I. Mucous glands: keep the skin moist
II. Granular poison glands: parotid and parotoid glands.
- Chromatophores: present in epidermis and dermis. Gives colorization.
· No scales except for some species.
Reptilian skin
· Thick, dry skin.
· Stratum corneum is hardened with dead keratinized cells.
· Can observe two layers in the epidermis.
- Outer epidermal generation
- Inner epidermal generation
· Therefore they can shed scales or called as molting.
· Scent producing glands are present in some.
· No mucous glands.
Bird skin
· Thin but horny scales are on legs and feet.
· Claws and beak present.
· Derivatives of the epidermis:
- Feathers
I. Contour feathers: Cover the body.
II. Flight feathers: Cover the wings. Large and stiffer.
III. Down feathers: lie beneath the contour feathers. Fluffy barbs.
IV. Bristle feathers: Short and stiff but the barbs are absent.
· Stratum corneum is not keratinized like in mammals.
· Dermis lacks ossification.
· Glands: mainly secrete lipids.
- Uropygial gland: Single, branched alveolar gland located above the base of the tail. Produces fatty and waxy secretion. This is later spread over feathers to make waterproof.
- Wax glands: lie in the external ear canal
Mammalian skin
· Thick epidermis.
· Transitional layers can be seen between stratum corneum and stratum germinativum.
· Stratum corneum is thick and forms foot pads in many mammals.
· Glands:
- Sebaceous glands: alveolar branched glands that produce oil and wax.
- Sweat glands: tubular coiled glands.
- Mammary glands
