Densities and Occurrence of Three Annelids with Description of the Species Enchytraeus albidus Henle, 1837 (Oligochaeta: Enchytraeidae) in Two Different Marine Regions South of Basrah Province, Iraq

This study's samples were collected from two stations monthly from January to December 2024. The first station represents the south of Shatt al-Basra River, west of Basrah Governorate, and the second station, Al-Faw, represents the estuary of Shatt al-Arab River, south of Basrah Governorate. Samples were collected using a 25*25cm square core for quantitative samples and by directly picking with forceps for qualitative samples. Three species of annelids were recorded, one of which belongs to the class Oligochaetes and two to the class Polychaetes. The highest density recorded at Al-Faw station was for the species Enchytraeus albidus, which reached 25 ind/m², while the highest density recorded at Shatt al-Basrah station was for the species Namalycastis indica, reaching 35 ind/m². References differed on the lengths of the Enchytraeidae worms, but in this study, they ranged between 10-17mm, their color was whitish to yellowish, and the number of body segments ranged from 37-39. The setae are straight or slightly curved between 3-5 in a bundle; pharyngeal gland 3 pairs in segments 4/5-6/7, yellowish blood. Clitellum gland cells were irregularly scattered. Chloragogen cells started from V but formed a dense layer from VI. The brain was slightly concave posteriorly. This study would provide a comprehensive data on the Annelid worms tolerating the Iraqi polluted environmental conditions while breaking down these pollutants.