JKAU: Mar. Sci., Vol. 21, No. 2, pp: 3-14 (2010 A.D. / 1431 A.H.) DOI : 10.4197/Mar. 21-2.1 The Early Development of the Sea Urchin Diadema setosum (Leske, 1778) in the region of North Jeddah, Red Sea Adel N. Guirguis Faculty of Marine Science, King Abdulaziz University, Jeddah, Saudi Arabia
[email protected]. Abstract. Changes in the gonads of the sea urchin, Diadema setosum in northern Jeddah on the Red Sea, were followed over a year. Maturation of gonads begins in April and spawning occurs mainly in early summer (from June to July). Spawning of some mature specimens was induced by KCl-injection. The optimal temperature for development was determined by incubation of batches of fertilized eggs at various temperatures (from 20 to 30oC). Early development proceeded rather rapidly at 25oC over a period of 3-5 days. The different stages of development from the onset of fertilization up to pluteus stage were described. Typical radial cleavage is recorded. Gastrulation is mainly by a combined process of embolic invagination and epiboly. Keywords: Early development, Sea Urchin, Diadema, Red Sea. Introduction Diadema setosum (Leske, 1778), is the most abundant diadematid echinoderm in the Red Sea. It is well known by its extremely long needle-like (up to 20 cm) spines (Soliman, 2001). It is the most common benthic echinoid on the rocky beach as well as near reefs, characterized by its black colour. During the day, Diadema is inactive, either resting in crevices at the bases of the coral reefs or aggregated in groups. In the evening, animals leave their resting places and crawl about some meters away in order to forage on the rocky bottom.