gastroderm

The gastroderm, also known as the gastrodermis, is the inner tissue layer of diploblastic animals such as cnidarians that lines the gastrovascular cavity. This layer forms the gut lining within a blind, single-cavity digestive system and participates in digestion and nutrient distribution.

Structurally, the gastroderm derives from the endoderm and consists of several cell types, including gland cells that secrete digestive enzymes into the cavity and nutritive (or nutritive-muscular) cells that absorb nutrients. Some cells may be ciliated to help circulate fluids within the cavity. The gastroderm is distinct from the outer epidermis, which contains protective cells such as nematocysts in cnidarians.

Functionally, digestion occurs both extracellularly in the gastrovascular cavity, via secreted enzymes, and intracellularly within gastrodermal cells. Nutrients are absorbed by these cells and then distributed by diffusion or circulation within the cavity, supporting the animal’s metabolic needs. The gastroderm also interacts with the mesoglea, the gelatinous matrix separating it from the outer epidermis.

Developmentally, the gastroderm arises from the endoderm in organisms with two primary germ layers and is a key feature of diploblastic body plans. In cnidarians, it lines the gastric cavity of both polyps and medusae, with variations in how it covers the pharynx and internal canals.

Overall, the gastroderm is the inner digestive tissue that enables digestion, absorption, and early nutrient distribution in cnidarians and related diploblastic groups.