Tetraclita ehsani sp. n. (Cirripedia, Tetraclitidae), a common intertidal barnacle from the Gulf of Oman, Iran

Abstract A new species of intertidal acorn barnacle Tetraclita ehsani sp. n. was identified from the Iranian coast in the Gulf of Oman. Tetraclita ehsani sp. n. inhabits low exposed rocky shores and also attaches to shells of molluscs and the barnacle Megabalanus species. Parietes of Tetraclita ehsani ranged from white to pink which is different from Tetraclita serrata (in South African waters), which has green parietes. Morphology of the tergum and cirrus III of Tetraclita ehsani sp. n. is distinctive from other described West Indian Ocean species which have pink or white parietes (Tetraclita rufotincta, Tetraclita achituvi and Tetraclita reni). The tergum of Tetraclita ehsani is very narrow and the basal margin is slightly concave or straight, in contrast to Tetraclita rufotincta and Tetraclita reni, in which the tergum are board and with a very concave basal margin. Cirrus I anterior ramus of both Tetraclita ehsani and Tetraclita reni is antenniform and thus differing from the cirrus I of Tetraclita rufotincta (see Chan et al. 2009). Cirrus III of Tetraclita ehsani sp. n. is non-antenniform and lacks multicuspidate type setae, which is different from Tetraclita reni by having an antenniform cirrus III and with multicuspidate setae.


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. T. rufotincta was subsequently recorded in the northwest coast of India (Wagh 1971(Wagh , 1972, the Red Sea (Achituv and Barnes 1978) and the Persian Gulf (Utinomi 1969). Ross (1999) additionally described T. achituvi Ross, 1999 and T. barnesorum Ross, 1999 from T. rufotincta in the Red Sea but subsequent molecular studies (Appelbaum et al. 2002) revealed T. barnesorum was a synonym to T. rufotincta. Ren (1989) described T. africana from Madagascar, but as this name was preoccupied and it was renamed T. reni Chan, Hsu & Tsai, 2009by Chan et al. (2009. In the West Indian Ocean, T. 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. (2007aChan et al. ( , 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.
Diagnosis. Parietes white or pink, tergum very narrow, basal margin slightly concave or almost straight, tergal spur long and narrow. Mandible with five teeth, labrum with 4 large sharp teeth on each side of the cutting edge. Anterior ramus of cirrus I antenniform.
Description. Parietes conical, white to pink or white with pink ribs (Fig. 1A), radii and alae narrow, sheath striate, parallel to base and about ½ height of wall, sheath white to dirty white, or pink. Parietes composed of 3-4 rows of honey comb parietal tubes (Fig. 1B). Scutum and tergum white (Fig. 1B, C, D). Scutum narrow, 1.5 times higher than wide, lower half of occludent margin with >10 oblique teeth, articular ridge sinuous, adductor ridge extremely developed, angular and extending to basal margin, adductor muscle pit shallow, seven distinct rostral and four to six lateral depressor crests (Fig. 1B, C, D), external surface smooth with faint horizon- tal striations (Fig. 1). Tergum long and narrow (length more than twice as width) with ten definite depressor crests, scutal margin slightly concave, spur long and narrow, external spur surface with a medial furrow, basi-scutal angle sharp and about 117.8°, upper carinal margin convex and basal margin slightly concave or straight (Fig. 1B, C, D). Carinal-basal angle (angle between the carinal and basal margin) is ~103° (Fig. 1C).  Mandibular palps elongate, setae on superior margin only, simple type setae at tip and serrulate setae at the middle region of the superior margin (Figs 2A, 3A, B, C). Labrum notched, notch shallow, four erect large teeth on each side of the cutting edge (Figs 2B, 3E-H). Mandible with five teeth excluding the inferior angle, first tooth separated from the remaining teeth, second and fourth teeth bidentate, third teeth tridentated fifth tooth small and located close to the fourth tooth, lower margin with >10 setae, height of setae similar to height of the fifth tooth, inferior angle sharp, with two large setae on tip, mandible surface with blade shaped serrulate type setae (Figs 2C, 3G-L). Maxillule notched, with two large and four small simple setae above notch, 11 setae in median cluster and 10 small and slender simple setae on the cutting margin below notch (Figs 2D, 3M-O). Maxilla bi-lobed, serrulate type setae at both lobes (Figs 2E, 3P-S).
Etymology. This species is named in honour of Ehsan Entezari-Zarch, B.Sc. student in Animal Biology at the University of Tehran, who unfortunately passed away during a field collection in October 2009.
Habitat. This species was present at the exposed low shores at intertidal zone, attaching on rocks but sometimes were observed on mollusk shells and on the shell surface of the barnacle Megabalanus species at the Gulf of Oman.
Distribution. At present, only known from the Iranian coast in the Gulf of Oman and absent from the Persian Gulf (see Shahdadi 2007).

Discussion
Tetraclita ehsani sp. n., from Iranian waters, shows diagnostic morphological characters that distinguish it from other known species in the Western Indian Ocean (T. rufotincta, T. reni, T. achituvi and T. serrata). All the Tetraclita in the West Indian Ocean have white to pink parietes except T. serrata Darwin, 1854 which has green parietes. In addition to the colour of the parietes, T. serrata has serrated lines on parietes surface and with a broader spur in tergum, when compared to Tetraclita ehsani. It is difficult to distinguish T. ehsani from T. reni, T. achituvi and T. rufotincta using the external shell morphology. T. ehsani can be, however, distinguished from the other species by the tergum morphology and arthropodal characters. The ter-gum of T. ehsani is very narrow and the basal region is slightly concave or almost straight, contrasting to the tergum of T. rufotincta and T. reni, which are board and with a strongly concave basal margin (Fig. 1E, F). The basi-carinal angle of T. ehsani sp. n. is ~100°, which is larger than that in T. reni (80°) and T. rufotincta (73°; Fig.  1C, D, E). The basi-scutal angle of the tergum of T. ehsani is ~120°, more angular than that of T. reni (150 °) (Fig. 1C, D, E; see Chan et al. 2009). Anterior ramus of the cirrus I of both T. ehsani and T. reni is antenniform, thus differing from T. rufotincta (see Chan et al. 2009). Cirrus III T. ehsani sp. n. is non-antenniform and lacks multicuspidate setae, which is different from T. 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. T. 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. T. reni is confined to southern Madagascar and adjacent waters and T. achituvi has been reported only from the Red Sea. T. Table1. Morphological comparison of Tetraclita ehsani sp. n. with other Tetraclita from the west Indian Ocean. T. serrata was not included into comparison as the shell colour of T. serrata is green, which is obviously different from other West Indian Ocean species. For morphology features of T. rufotincta, T. reni and T. achituvi, see Pilsbry (1916), Chan et al. (2009) and Ross (1999).

Characters
Tetraclita ehsani sp. n. 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 T. 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 T. ehsani.