Abstract Clausidium Kossman, 1874 is a genus of copepods that is found in subtropical to temperate coastal areas. All species of the genus occur on the bodies of mud shrimp of the families Callianassidae and Upogebiidae. Based on morphological data from light scanning and confocal laser scanning microscopy, there are four species of Clausidium copepod in Iran. In this study we address Clausidium iranensis Sepahvand, Kihara and Boxshall, 2019 and Clausidium persiaensis Sepahvand and Kihara, 2017 that were reported on the body of the burrowing shrimps Neocallichirus jousseaumei (Nobili, 1904) and Callianidea typa Milne Edwards, 1837, respectively. We undertook analyses of mitochondrial DNA gene sequences (CO1) to evaluate taxonomic status and taxonomic relationships of the Clausidium species. The result demonstrates that two major clades, with strong support, can be identified within the Clausidium copepods in the southern waters of Iran, representing distinct taxonomic entities at the species rank. Our data indicate that CO1 can be a powerful tool for species identification and delimitation. In the case of Clausidium copepods, the general utility of CO1 for taxonomic relationship inferences within a genus or a family is still under investigated. Our study adds the first genetic data from these copepods from the Persian Gulf and Gulf of Oman.

Abstract A new species of the Clausidium Kossmann, 1874 copepods is described, illustrated and provided by Confocal Laser Scanning Microscope photo on the basis of specimens from the gill chamber of Callianidea typa H. Milne Edwards, 1837 from the Iranian coast of the Persian Gulf. Clausidium persiaensis sp. nov is unique in the possession of a fine spine on endopod-1 of the antennae, large blade-like setae with an acute tip on P1, and the shape of P5 and the anal somite. The new species extends the group distribution into the northwest Indian Ocean and represents the first records of the genus in Iran.

Mud shrimps (formerly Thalassinidea) are common burrow dwelling decapod crustaceans in the littoral zone of the Persian Gulf and Gulf of Oman. Their burrow morphology was investigated using foam casting methods. The present study shows that the burrow morphology in Upogebia carinicauda is not consistent and the recorded variations are based on habitat type and some physical characteristics of sediments. Adult burrow morphology in sandy-muddy substrate with shells, and boulder field habitats were Y-shaped and complex burrows of horizontal channels with turning chambers and vertical connections to internal passages or crevices of boulders, respectively. In burrows of U. carinicauda, some narrow passages, connected to the upper part of adult burrows in sandy-muddy habitats, belong to juveniles. Another species, Neocallichirus jousseaumei was found under boulders in sandy-muddy habitats of the Gulf of Oman and Qeshm Island, Persian Gulf. Since this type of habitat is special in some features, no conspicuous ex-current openings (usually obvious as conical mounds of extruded sediment) have been observed on the sediment surface; as these were hidden among the boulders surrounded by mixed sand and shells. The only method for observing this type of burrow was to remove the boulders by hand or lever.