Introduction

Tetraclita species are common rocky intertidal acorn barnacles in the tropical and subtropical waters of the world (Newman and Ross 1976). Tetraclita squamosa Bruguière, 1789 had been recorded worldwide and was considered to be composed of nine sub-species due to high degree of morphological variations (Newman and Ross 1976). Tetraclita squamosa has since been split into 23 species using morphological and molecular approaches (Chan et al. 2007a, b, c), but the taxonomy of the species in the West Indian Ocean has still received scant attention (Chan et al. 2009). Pilsbry (1916) described Tetraclita rufotincta (= Tetraclita squamosa rufotincta Pilsbry, 1916) from Yemen and Zanzibar, and designated Yemen as the type locality. Tetraclita rufotincta was subsequently recorded in the northwest coast of India (Wagh 1971, 1972), the Red Sea (Achituv and Barnes 1978) and the Persian Gulf (Utinomi 1969). Ross (1999) additionally described Tetraclita achituvi Ross, 1999 and Tetraclita barnesorum Ross, 1999 from Tetraclita rufotincta in the Red Sea but subsequent molecular studies (Appelbaum et al. 2002) revealed Tetraclita barnesorum was a synonym to Tetraclita rufotincta. Ren (1989) described Tetraclita africana from Madagascar, but as this name was preoccupied and it was renamed Tetraclita reni Chan, Hsu & Tsai, 2009 by Chan et al. (2009). In the West Indian Ocean, Tetraclita reni is distributed in southern Madagascar and adjacent waters (Chan et al. 2009).

Taxonomic studies of Iranian barnacles after Utinomi (1969) are scant (Jones 1968; Southward and Newman 2003). Recently, extensive barnacle collections was carried out by Shahdadi (2007), Shahdadi and Sari (2011) on intertidal barnacles of the Persian Gulf and Gulf of Oman. Tetraclita rufotincta is common in the intertidal of the Persian Gulf (Shahdadi 2007). However, Tetraclita specimens collected from exposed rocky shores at the Gulf of Oman, Iran were morphologically different from other known Tetraclita species of the West Indian Ocean, suggesting that this is a new species. The Tetraclita specimens from the Gulf of Oman were examined by one of us (BKK Chan) using COI molecular markers, which showed a large genetic divergence from all known species in the West Indian Ocean (sequence of Tetraclita specimen from Gulf of Oman submitted to GenBank, unpublished data for phylogenetic comparisons). This further confirms the Tetraclita collected from the Gulf of Oman is a new species and described herein.

Materials and methods

Tetraclita specimens were collected from the low intertidal shores at Ramin, Chabahar (25°16'N, 60°44'E) and Tis, Chabahar Bay (25°16'N, 60°40'E), Gulf of Oman, Iran. Barnacles were preserved in 95% Ethanol upon collection. The opercular plates, cirri and mouth parts were dissected and observed under compound light microscopes. The first three pairs of cirri and mouth parts were further investigated using a FEI Quanta 200 Scanning Electron Microscope (SEM) following Chan et al. (2007a, c, 2009). Terminology in describing the setae follows Chan et al. (2008). The COI barcode region was sequenced from the somatic body of the Tetraclita (paratype, ASIZCR 000231) collected from Chabahar, Gulf of Oman. DNA extraction and PCR protocol followed Chan et al. (2007a, c) and sequence was deposited in the GenBank.

The holotype and two paratypes are deposited in the Zoological Museum, University of Tehran (ZUTC) and one of the paratype was deposited in the Biodiversity Museum, Academia Sinica, Taiwan (ASIZCR).

Systematics Superfamily Tetraclitoidea Gruvel, 1903
Family Tetraclitidae Gruvel, 1903
Tetraclitinae Gruvel, 1903
Tetraclita Schumacher, 1817 Discussion

Tetraclita ehsani sp. n., from Iranian waters, shows diagnostic morphological characters that distinguish it from other known species in the Western Indian Ocean (Tetraclita rufotincta, Tetraclita reni, Tetraclita achituvi and Tetraclita serrata). All the Tetraclita in the West Indian Ocean have white to pink parietes except Tetraclita serrata Darwin, 1854 which has green parietes. In addition to the colour of the parietes, Tetraclita serrata has serrated lines on parietes surface and with a broader spur in tergum, when compared to Tetraclita ehsani. It is difficult to distinguish Tetraclita ehsani from Tetraclita reni, Tetraclita achituvi and Tetraclita rufotincta using the external shell morphology. Tetraclita ehsani can be, however, distinguished from the other species by the tergum morphology and arthropodal characters. The tergum of Tetraclita ehsani is very narrow and the basal region is slightly concave or almost straight, contrasting to the tergum of Tetraclita rufotincta and Tetraclita reni, which are board and with a strongly concave basal margin (Fig. 1E, F). The basi-carinal angle of Tetraclita ehsani sp. n. is ~100°, which is larger than that in Tetraclita reni (80°) and Tetraclita rufotincta (73°; Fig. 1C, D, E). The basi-scutal angle of the tergum of Tetraclita ehsani is ~120°, more angular than that of Tetraclita reni (150 °) (Fig. 1C, D, E; see Chan et al. 2009). Anterior ramus of the cirrus I of both Tetraclita ehsani and Tetraclita reni is antenniform, thus differing from Tetraclita rufotincta (see Chan et al. 2009). Cirrus III Tetraclita ehsani sp. n. is non-antenniform and lacks multicuspidate setae, which is different from Tetraclita reni, in which the both anterior and posterior rami are antenniform and possess multicuspidate setae (see Chan et al. 2008) (Table 1).

The biogeography of Tetraclita species in the West Indian Ocean appears to be distinctive between different oceanographic systems. Tetraclita rufotincta has the widest distribution, covering the Persian Gulf, the Red Sea and the East African coast and absent from South Africa and southern Madagascar. Tetraclita reni is confined to southern Madagascar and adjacent waters and Tetraclita achituvi has been reported only from the Red Sea. Tetraclita ehsani has not been recorded in other parts of the Western Indian Ocean, except from the Iranian coast in the Gulf of Oman and it is absent from the Persian Gulf. It may be possible that Tetraclita ehsani is common in the Arabian Sea. It is essential to conduct further biodiversity surveys in the Arabian Sea region, including the west coast of India (see Wagh 1972) to ascertain the geographic distribution of Tetraclita ehsani.