stomum

The stomum, commonly referred to as the mouth or oral aperture, is a fundamental anatomical feature found in many invertebrate organisms, particularly in cnidarians such as jellyfish, corals, and sea anemones. Unlike vertebrates, which possess a distinct mouth surrounded by lips and teeth, the stomum serves as a central opening for both ingestion and expulsion of waste, functioning as both an intake and an exit point for the digestive system.

In cnidarians, the stomum is encircled by tentacles, which often contain specialized cells called cnidocytes. These cells release harpoons-like structures called nematocysts to capture prey. Once prey is immobilized, it is directed toward the stomum, where it is ingested. The digestive process occurs primarily within the gastrovascular cavity, a single-chambered system branching from the stomum, allowing for both extracellular and intracellular digestion.

The stomum plays a crucial role in the organism’s survival, facilitating not only feeding but also gas exchange and waste removal. Its simple yet efficient design reflects the evolutionary adaptations of cnidarians to their aquatic environments. While the stomum is absent in more complex bilaterally symmetrical animals, it remains a defining characteristic of radially symmetrical organisms like jellyfish and corals, highlighting its significance in early evolutionary biology.