Tetractinellid and hadromerid sponges of the Sultanate of Oman

The Sultanate of Oman harbours rich populations of sponges, especially in the four coral reef areas (Musandam Peninsula, Muscat coast & Daymaniyat islands, coasts of Masirah Island, and the Khuriya Muriya Islands). Up till now, apart from a few incidental samples, the sponges of Oman were known only from five dredge stations made by the John Murray Expedition 1933-1934 off the south coasts of Oman, near the Khuriya Muriya Islands, between 13.5 and 1415 m. Descriptions of the sponges obtained in these dredges were published by Burton (1959) and the specimens are deposited in the collections of the Natural History Museum, London. To complement these dredge samples, we recently obtained samples collected by SCUBA and shore collecting, mostly from the northern part of Oman, deposited in the collections of the Zoological Museum of the University of Amsterdam. We studied the combined Oman collections of the Amsterdam and London Museums. In the present contribution we treat the species belonging to the tetractinellid and hadromerid Demospongiae. The sponges of the Zoological Museum of Amsterdam are fully described and illustrated, those of the John Murray Expedition are annotated and illustrated here with habit photographs, as these were entirely lacking from Burton’s (1959) report. The collection studied here contains 30 species, two of which are new to science, six are up till now known only from Oman waters, while the remaining 24 species are shared with other areas. The Indian subcontinent shares the most species with Oman, followed by East African areas, while the nearby Arabian coasts share only few species, probably due to the poor knowledge of sponges from this region.