zonary

Zonary is an adjective meaning relating to a zone or organized in a belt or circular band. The term derives from the Latin zona, meaning a belt or girdle. In scientific usage, zonary describes structures that are arranged into defined zones around an axis or around a central point.

In mammalian anatomy, zonary placenta refers to a placental type in which exchange tissue forms a continuous band around the chorion, enclosing the embryo along a circumference. This arrangement is characteristic of the order Carnivora, including canids (dogs), felids (cats), ursids (bears), and pinnipeds (seals and sea lions). The zonary zone may be accompanied by transitional tissue layers and, in some species, by areas that differ in pigmentation or structure. Zonary placentation contrasts with other patterns such as diffuse placenta (villous tissue spread over most of the surface), cotyledonary placenta (multiple placentomes in discrete patches), and discoid placenta (one or few disc-shaped areas). The zonary layout supports maternal–fetal exchange along the circumferential band.

Beyond placentation, zonary is used more broadly to describe anything arranged in defined zones or bands, such as zonary patterns in geology or ecology that show spatial segmentation. In these contexts, zonation refers to the distribution of features across parallel or concentric zones.

See also: Placenta types, Zonation, Zonation in ecology.