Amphioxus
The outer acellular cuticle is secreted by underlying epithelial cells.
The epidermis is a layer of simple columnar epithelium cells with scattered unicellular glands.
The dermis is a very thin layer of dense collagen fibers.
Lamprey
The outer cuticle or slime layer is secreted by underlying epithelial cells.
The epidermis is a stratified layer of epithelium with many unicellular glands.
Teeth composed of keratinized tissue may be present around the mouth opening.
The dermis is a dense layer of collagen fibers with some pigment cells (chromatophores) present.
A layer of pigment cells may be found between the dermis and hypodermis.
A thin hypodermis with adipose cells is present.
Shark
The outer cuticle or slime layer is secreted by underlying epithelial cells.
The epidermis is a stratified layer of epithelium with many unicellular glands and some pigment cells.
Multicellular glands are present in some species and are usually associated with spines used in defense.
Placoid scales (denticles), with the same composition as teeth, develop from the interface of the epidermis and dermis. Placoid scales grow and extend through the epithelial layer to form the rough skin surface. The outer enamel of the placoid scale is secreted by the epithelial layer before the scale emerges, and the underlying dentin is a product of the dermal tissues. There is a pulp cavity in the core at the base of each tooth-like placoid scale.
The dermis is a dense layer of collagen and elastic fibers with some pigment cells present
A thin hypodermis is present.
Bony Fish
The outer cuticle or slime layer is secreted by underlying epithelial cells.
The epidermis is a stratified layer of epithelium with many unicellular glands. Multicellular glands are present in some species and are usually associated with fin spines used in defense.
Keratinization, if present is limited to special structures such as head tubercles and scraping surfaces of the lips.
Dermal scales are present in most bony fish. In polypterids the scales are a primitive ganoid type, with a layer of enamel (ganoine) at the surface and dentin and thick lamellar bone beneath. In the gar there is a ganoid surface with a thin layer of lamellar bone beneath. In other actinopterygians the scales are a thin layer of acellular bone and a supporting fibrous tissue.
The dermis is a dense layer of collagen and elastic fibers with some pigment cells present
There is also a hypodermis.
Amphibians
Most amphibians retain a slime cuticle, but those with a well keratinized surface usually do not.
The beginning of the appearance of the stratum granulosum, and stratum corneum coincides with the process of keratin formation in the epidermis
Multicellular poison glands and mucous glands are usually present.
The moist surface of those species lacking a significantly keratinized surface is often vital to the process of cutaneous respiration.
The stratified epithelium of the epidermis may show special areas of keratinization, may be slightly keratinized over most of the body, or may be well keratinized and dry over much of the surface as in most bufonid toads.
Some pigment may be present in the epidermis, but most chromatophores reside in the dermis.
Dermal scales are absent in salamanders and frogs, but may remain in some species of apodans as annuli (rings) beneath the epidermis in the body segments. These dermal scales are also called osteoderms.
In some species the dermis may be divided into a superficial zone of loose connective tissue and a deeper zone of dense connective tissue.
A hypodermis with adipose cells is present.
Reptiles
The integument of reptiles lacks a slime or mucous covering.
The epidermis is highly keratinized and dry.
There are few glands over the body surface, and those that are present are large multicellular glands on the chin, head, legs, or near the vent.
Keratinized epidermal scales grow from the epithelial covering on most of the body.
Special keratinized features include turtle beaks, nails or claws, spines, and horns.
The dermis may be divided into the superficial zone of loose connective tissue and a deeper zone of dense connective tissue as is common to tetrapods.
Dermal bone as remnants of dermal scales may be present deep to the belly scales of crocodilians, under the large dorsal scales of crocodilians and a few lizard species, and as part of the turtle’s shell found beneath the surface epidermal scale plates.
A hypodermis with adipose cells is present.
Birds
The epidermis of birds is dry, but extremely thin.
The epidermis has few glands. A pair of uropygeal glands is located near the base of the tail and birds actively use their beaks to spread oily secretions from these glands onto their feathers.
Keratinized epidermal specializations include beaks, scales, claws, horns, and feathers.
Think of feathers as highly modified epidermal scales.
Smooth muscles in the dermis of the skin called erector muscles cause feathers to rise or fluff out.
The dermis may be divided into the superficial zone of loose connective tissue, which is particularly loose in birds, and a deeper zone of dense connective tissue.
A hypodermis with adipose cells is present.
Mammals
The epidermis of mammals is dry and thick.
Hair is a keratinized outgrowth of the epidermis (as are feathers and the epidermal scales of reptiles, birds, and mammals)
Epidermal scales are seen covering armadillos, and on the tails of some rodents, but the scales of pangolins appear to be modified hairs as is the rhinoceros horn.
Other keratinized structures include horn, nails, claws, hooves, and baleen.
There are usually abundant sebaceous glands.
Other glands include various types of sweat glands, scent glands, and mammary glands.
The dermis is highly developed and thick in many species. It is divided into the superficial zone of loose connective tissue (papillary layer) and a deeper zone of dense connective tissue (reticular layer).
Arrector pili muscles are present in the dermis to raise the hairs (goose bumps).
A hypodermis with adipose cells is present.