LAUSR

* Correspondence: [email protected] The Gulf of Oman is located between the Persian Gulf and Arabian Sea. The surface of the gulf is about 94,000 m2. Based on the International Hydrographic Organization, it is defined in the western part by an imaginary line running from Minab, in Iranian waters (north limitation), to Qabr al-Hindi, in the coastal waters of Oman (south limitation). In the eastern part it is limited from Ras Jiwani, on the border of Iran and Pakistan (in the north), to Ras al-Hadd, on the Oman coast (in the south). The Gulf of Oman is a deep area that reaches to 3000 m in its deepest part (in the east) (Reynolds, 1993). Salinity and monsoons are the most important factors in the gulf that can affect physical and biological factors (such as temperature and biodiversity) in the area. The monsoons bring southwardly blowing cool winds in summer and northwardly blowing winds in winter. For this reason, the temperature is balanced between 22 and 31 °C (Reynolds, 1993; Piontkovski et al., 2012). Salinity can reach 37 psu in the area (Reynolds, 1993). A wide variety of habitats can be found in the intertidal region of the Gulf of Oman, such as muddy-sandy habitats in sheltered areas to sandy and rocky shores in the high-energy region (Naderloo, 2017). A high diversity of marine algae covers the coastal waters of the Gulf of Oman (Sohrabipour and Rabiei, 2007; Gharanjik and Rohani-Ghadikolaei, 2010). For this reason, we can conclude that a high diversity of marine animals inhabit the gulf. Until 2018 about 33,400 species of animals had been recorded from the Persian Gulf and the Gulf of Oman (Maghsoudlou et al., 2017). There are more than 1400 pycnogonid species in the world that can be found on shorelines down to deep water in different habitats from tropical to polar waters (Lucena et al., 2015; Brenneis et al., 2017). The genus Endeis Philippi, 1843, belonging to the family Endeidae Norman, 1908, is a cosmopolitan genus, most often recorded in shallow waters. It currently possesses 18 valid species (http://www. marinespecies.org/aphia.php?p=taxdetails&id=134588). Because of the great similarity among the species of Endeis (Fry and Hedgpeth, 1969), it is a challenging task to identify a single specimen to the species level (Child, 1992). Females of this genus are especially very difficult to separate when not accompanied by the males (Stock, 1968; Clark, 1973). This is probably one of the genera most in need of revision among the pycnogonids (Marcus, 1940; Müller and Krapp, 2009). To date, there is no record of this genus for the Persian Gulf and the Gulf of Oman. Two species, Endeis meridionalis (Böhm, 1879) and E. mollis (Carpenter, 1904), have been previously recorded from Pakistan (Clifton) (see Gul and Ghani, 2012). Therefore, this is the first record of an Endeis pycnogonid, E. biseriata, from Iran, in the Gulf of Oman. A checklist of the species of Pycnogonida of the Persian Gulf and the Gulf of Oman is also provided. Abstract: This is the first record of a pycnogonid for the Iranian coast. It is also the first record of an Endeis, and of Endeis biseriata, for the waters of the Gulf of Oman. A single specimen was collected in an algal bed of Padina sp., along Chabahar Bay, in February 2017. It is deposited in the Zoology Museum of the University of Hormozgan. E. biseriata is probably a native Indo-Pacific species that now has a wide world distribution, being probably pantropical. Morphological and ecological notes, as well as the distribution range of E. biseriata and a checklist of the species of Pycnogonida from the region, are also provided.