Evolution and population genetic structure of marine species across the Persian Gulf and Gulf of Oman are shaped by two complex factors: the geological history and the present pattern of marine currents. Characterizing and comparing the genetic structures of co-existing species, such as host–parasite associations, allow the discrimination of the relative importance of environmental factors and life history traits that influenced gene flow and demographic events. In this study, we compare two associated Clausidium copepod species (C. persiaensis Sepahvand & Kihara 2017 and C. iranensis Sepahvand, Kihara & Boxshall 2019) along the south coast of Iran in two geological settings. We analysed partial nucleotide sequences of the mtCOI gene using divergence estimates (FST) and haplotype networks to infer intraspecific population connectivity in the two Gulfs. The results obtained demonstrate the existence of two genetically and geographically distinct clades, corresponding to the Persian Gulf and Gulf of Oman populations. Our results also indicate high diversity, population expansion and high connectivity among populations of C. persiaensis and C. iranensis in the Persian Gulf and Gulf of Oman.

Two new species of Clausidium copepods were collected on the bodies of ghost shrimps from the Iranian coast of the Gulf of Oman. Clausidium makranensis sp. nov. and Clausidium sarii sp. nov. are described from the large chelipeds of Neocallichirus natalensis and Corallianassa martensi, respectively. Clausidium makranensis sp. nov. is distinguishable from its congeners by the unique anal somite that is armed with sclerotized hooks on each side. Clausidium sarii sp. nov. can be differentiated from its congeners by the armature and shape of leg 5.

The infauna of Chabahar Bay (Iranian Coast of the Gulf of Oman) was investigated using shallow water (less than 10 m) grab-samples between June 2013 and March 2014. The magelonid fauna of these samples was studied and prioritized, with four species being present: M. fauchaldi sp. nov., M. symmetrica, M. cf. cincta and M. crenulifrons. The new species differs from all known magelonid species within the Persian Gulf region in possessing polydentate abdominal hooks. A fifth species, currently undescribed, was also found. The validity of M. pulchella originally described from Kuwait is discussed in light of its closeness to M. crenulifrons. The main distinguishing feature between the two species is the presence or absence of crenulation of the anterior prostomial margin, a character shown to be variable in M. crenulifrons. Although differences between the type specimens of both species suggests M. pulchella to be a valid species, examination of further material and DNA analysis is needed.

A large well-established population of the grapsoid crab Percnon affine (H. Milne Edwards, 1853) was observed in the rocky low-intertidal zone of Chabahar Bay, along the Iranian coasts of the Gulf of Oman. This is the first record of P. affine from the northern Indian Ocean.

Three brachyuran species of the family Xanthidae, Atergatis ocyroe, Macromedaeus voeltzkowi and Macromedaeus quinquedentatus are recorded from the Iranian coast of the Gulf of Oman. These specimens were collected in 2009 and 2010 from the Iranian waters of the Gulf of Oman. Among these species, A. ocyroe is a new record for the Gulf of Oman and M. quinquedentatus is a new record for the Iranian coast. This is the second record of M. voeltzkowi from the Iranian coast, whereas there is still no record from the Arabian coast of the Gulf of Oman. The diagnostic characteristics of the species and some taxonomic remarks are reported upon in this paper.

The mud shrimps of Iran are not well known. Material for the present study was collected from 21 out of 51 intertidal localities from the Persian Gulf and Gulf of Oman, Iran. In total, 11 species were found along the Iranian coast. These were belonging to three families, including Upogebiidae (Upogebia carinicauda, U. darwinii and U. pseudochelata), Callianassidae (Neocallichirus jousseaumei, N. calmani, Callichirus masoomi, Corallianassa coutierei, Michaelcallianassa indica, Paratrypaea bouvieri and Gourretia coolibah) and Callianideidae (Callianidea typa). Geographical distributions of the species were considered and the results show that each species is totally dependent on a special type of habitat. Comparing different types of habitat, sandy and muddy substrates of the intertidal and shallow subtidal zone are found as the dominant habitat type for all species, but some species have a preference for boulder dominated coasts or occupy already existing holes and crevices in the boulder and bedrocks. In addition, the world distribution of each species was considered, and according to their present recorded localities, these are grouped into two distributional categories including the Indo-West Pacific region and one in a broader area of the Indo-Pacific.

In the present study, chthamalid barnacles of the Persian Gulf and Gulf of Oman were collected from the coastal zone of Iran. Extensive collecting of different habitat types resulted in finding two species: Chthamalus barnesi and Microeuraphia permitini. In addition to the Persian Gulf and Gulf of Oman, the former species was also collected from the Red Sea and Gulf of Aden. Both species are described and compared for their key characters with some representative members of the genera from other parts of the world.

The present paper reports the first record of one antennarid species from the Gulf of Oman and the second record of another frogfish from the Arabian Sea coasts of Oman. The record of Antennarius coccineus is a north-eastern extension of its distribution in Omani waters. Antennarius indicus was recorded for the second time from the Arabian Sea coasts of Oman.

Specimens of the swimming crabs, Thalamita admete and Thalamita prymna, were collected on intertidal zones of Chabahar Bay (Gulf of Oman) in 2007. A literature review on the distribution of these two species revealed that this is the first report of T. admete from the Gulf of Oman and T. prymna from the Iranian coasts of the Gulf of Oman. A note on the morphological features of these specimens is given in this paper.