👉 Oligochaeta, also known as polychaetes or polychaos, is a group of organisms that have a single cell and are found in aquatic environments. They are characterized by their unique shape, which is formed by the fusion of two cells. This process results in a spherical-shaped organism with three bodies (pulmonary, digestive, and sexual) and no internal organs or tissues. Oligochaetes can be classified into several groups based on their size, number of cells