By Nina Thach

The integument consists of the dermis and epidermis. The epidermis is made up of layers of simple squamous epithelial cells. Depending on the vertebrate examined, there may be many of few layers in the epidermis, but the stratum: the stratum germinativum is always present as it is the living layer of cells. Many amniotic land vertebrates including the cat have a stratum germinativum along with other layers overlying it including a stratum corneum. The stratum corneum is made from layers of dead, keratinized epithelial cells. This hardness and strength offers protection and water resistance on land (Kardong 2015).

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Figure 1. Apical view of amphibian skin. Photo credit: H. Schutz.

Amphiuma, lampreys and sharks lack a stratum corneum along with many of the other overlying layers and have a very thin epidermis. In
Amphiuma as in many other amphibians,there are special integumentary capillary beds that extend from the dermis into the thin epidermis, and through cutaeneous respiration, they can regulate the internal levels of carbon dioxide in the body by providing an additional region of gas exchange. The thin membrane allows for diffusion of carbon dioxide from their body to the external environment (Toews 1970). Also contained in the dermis are mucous glands, which produce mucous that helps inhibit pathogens and maintain skin moisture needed for efficient cutaneous respiration (Kardong 2015).


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Figure 2. Cranial view of A. tridactlyum lateral line system. Photo credit: M. Lang & N. Thach.

Comparative Anatomy:


Both the shark and Amphiuma have a lateral line system. In the image above, the lateral line system is made of recessed grooves around the nose
that encircle the eyes, and run along the lateral sides of the body and tail. The function of this system is to sense vibrations and directional movement in the water via specialized mechanically stimulated receptors called hair cells which are also present in the inner ear and semi-circular canals. These are triggered by variations in water flow around the animal and provide additional sensory perception (Kardong 2015). Cat's lack a lateral line system, but have similar types of cells in the inner ear for hearing and balance. In regards to the integument of the cat, it's comprised of thick skin (both in multiple layers of epidermis and a thick dermis) and keratinous hair and claws as well as mammary glands derived form the oil and sweat glands. These integumentary adaptations are cat's way of surviving terrestrial conditions and mammary glands are a defining characteristic of mammals (synapomorphy). As mentioned above, keratin is not present in the Amphiuma skin (Kardong, 2015).


References

Kardong, K. V. (2015). Vertebrates: Comparative anatomy, function, evolution. Seventh edition. New York: McGraw Hill Education. 220, 694 p.

Toews, D. P., Shelton, G., and Randall, D.J. (1970). Gas tensions in the lungs and major blood vessels of the urodele amphibian, amphiuma tridactylum. Vancouver: University of British Columbia. 61 p.