tegument

Tegument is a term used in biology to denote an outer covering or protective layer that envelopes an organism or structure. The word comes from the Latin tegumentum, meaning covering or skin. In zoology, tegument generally refers to the animal’s outer covering (the integument), including the skin and its associated structures, and in many invertebrates the epidermis is referred to as the tegument.

In parasitology, tegument denotes a specialized outer syncytial layer that covers the bodies of certain flatworms, including trematodes (flukes) and cestodes (tapeworms). This living, multinucleate layer functions in nutrient absorption, osmoregulation, secretion, and immune evasion. The tegument is often studded with microtriches, microscopic projections that increase surface area and facilitate exchange with the host environment. It provides protection against host digestive enzymes and immune defenses.

In botany and seed biology, teguments are the protective layers surrounding the ovule’s nucellus, which, after fertilization, form the seed coat. The tegument is produced by the integuments of the ovule and becomes the seed coat (including structures such as the testa and tegmen), contributing to protection, dormancy regulation, and germination behavior.

Across diverse groups, tegument denotes an outer protective layer with specialized roles. In many parasites, it is a metabolically active, absorptive interface; in plants, it becomes the seed coat, and in general zoological use, it refers to the exterior integument or skin of an organism.