Settlement behaviour and description of the lessepsian immigrant of the serpulid polychaete Pomatoleios kraussii in the Suez Bay

Pomatoleios kraussii is a lessepsian migrant in the Suez Canal and form the most abundant serpulid (sessile polychaetes) in Suez Bay. It firstly appeared in western side of the Suez Gulf. But it is now present in all regions of Suez Gulf. P. kraussii live at the intertidal zone in the Suez Bay. It forms dense aggregations in shallow water on natural hard submerged substrates. A quadrate made of wood with 20 × 20 cm was used to collect the dense populations of P. kraussii, at monthly intervals from January to December 2008. The population density of P. kraussii reached 193797 worms/m2 and its annual settlement reached 16150 worms/m2 in the Bay. The species appears preferentially in Winter while its least presence was detected in summer. The lengths of both the worm body and tube are mentioned for a year. The tube is extending from 19 mm to 42 mm in length. The worm body length ranged from 7 mm to 35 mm. There is a direct correlation between the lengths of both the tube and the worm. This means that the greater the length of the worm the greater the length of the tube. Tube is pale blue in colour and carries a projecting flattened dorsal ridge. Operculum is flat with winged stalk and desk shaped. No collar setae. The body symmetrical, with 6 thoracic setigers and long abdomen. Thoracic dorsal setae limpate capillaries; ventral uncini with numerous teeth and gouge. All body regions are described in details.