Tunica (biology)

In biology, a tunica (/ˈtuːnᵻkə/) (plural tunicae) is a layer, coat, sheath, or similar covering. The word came to English from the New Latin of science and medicine. Its literal sense is about the same as that of the word tunic, with which it is cognate. In biology one of its senses used to be the taxonomic name of a genus of plants, but the nomenclature has been revised and those plants are now included in the genus Petrorhagia.

In modern biology in general, tunica occurs as a technical or anatomical term mainly in botany and zoology. It usually refers to membranous structures that line or cover particular organs. In many such contexts tunica is used interchangeably with tunic according to preference. An organ or organism that has a tunic(a) may be said to be tunicate, as in a tunicate bulb. This adjective tunicate is not to be confused with the noun tunicate, which refers to a member of the subphylum Tunicata.

In botany there are several contexts for the term.

As an anatomical or morphological reference in zoology, tunica has a range of applications to membranous structures in anatomy, including human anatomy. Such structures are generally coverings or capsules of organs, but also may be linings of cavities. In some cases, such as the walls of macroscopic blood vessels, layers of the tissue of the walls, whether inner, intermediate, or outer, are called tunica of one kind or another. Examples follow, but neither the list nor the discussions are exhaustive.

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