Pinctada phuketensis sp. nov. (Bivalvia, Ostreida, Margaritidae), a new pearl oyster species from Phuket, western coast of Thailand Author Somrup, Supannee https://orcid.org/0000-0003-3217-098X Key Laboratory of Mariculture, Ministry of Education, Ocean University of China, Qingdao 266003, China & Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok 10900, Thailand Author Sangsawang, Akkarasiri Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok 10900, Thailand ffisais@ku.ac.th Author McMillan, Nichanun Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok 10900, Thailand Author Winitchai, Supanida Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok 10900, Thailand Author Inthoncharoen, Jitti Kasetsart Agricultural and Agro-Industrial Product Improvement Institute (KAPI), Kasetsart University, Bangkok 10900, Thailand Author Liu, Shikai https://orcid.org/0000-0001-5777-489X Key Laboratory of Mariculture, Ministry of Education, Ocean University of China, Qingdao 266003, China liushk@ouc.edu.cn Author Muangmai, Narongrit https://orcid.org/0000-0001-7954-7348 Department of Aquaculture, Faculty of Fisheries, Kasetsart University, Bangkok 10900, Thailand & Phuket Pearl Industry, Co. Ltd., Phuket 83000, Thailand ffisnrm@ku.ac.th text ZooKeys 2022 2022-09-02 1119 181 195 http://dx.doi.org/10.3897/zookeys.1119.87724 journal article http://dx.doi.org/10.3897/zookeys.1119.87724 1313-2970-1119-181 A258BC8E872546229FC9A0701B2EBA54 7BEC9D7178D25AB881401B2E2C58B1B1 Pinctada phuketensis Somrup, Sangsawang, Liu & Muangmai sp. nov. Figs 1 , 2 , 3 Type locality. Dok Mai Island, Phuket Province, Thailand, 7°47.84'N , 98°31.84'E , at 5-10 m depth. Material examined. Holotype : KUMF.MOLL.1206 (NMR079) (Figs 1B , 2 ), 10 August 2021 , collected by SCUBA diving. Paratypes : two specimens , KUMF.MOLL.1204 (NMR077) (Fig. 1A ) and KUMF.MOLL.1205 (NMR078) (Fig. 1C ), 10 August 2021 , collected by SCUBA diving. Non-type material. KUMF.MOLL.1201-KUMF.MOLL.1203, 5 February 2022 , collected by SCUBA diving. All examined specimens were collected from the type locality by S. Somrup. Figure 1. Shell of Pinctada phuketensis sp. nov. from Dok Mai Island, Phuket , Thailand . External and internal views of left and right valves A paratype , KUMF.MOLL.1204 (NMR077) (scale bar: 5 cm ) B holotype , KUMF.MOLL.1206 (NMRA079) C paratype , KUMF.MOLL.1205 (NMR078) (scale bar: 4 cm ). Abbreviations: LV, left valve; RV, right valve. Diagnosis. Shell is anteriorly oblique, inequilateral, laterally compressed, and subcircular to quadrate in outline. Byssal notch is small, narrow and slit-like. Hinge teeth are absent. Adductor muscle scar is kidney- or bean-shaped with the distal extremities of the posterior pedo-byssal retractor muscle scar inserted into the concavity on its anterior border. The non-nacreous border is relatively pale to transparent, with few dark brown or black blotches. Description. Holotype, KUMF.MOLL.1206 (NMR079), specimen is approximately 60.4 mm height, 53.1 mm length, 23.1 mm depth, and 22.9 mm width (Figs 1B , 2 ). Paratypes, KUMF.MOLL.1204 (NMR077) and KUMF.MOLL.1205 (NMR078), 53 and 78 mm height, 46 and 75 length mm, 8.3 and 43.7 mm depth, and 38.5 and 54 mm width (Fig. 1A, C ), respectively. Figure 2. Right valve of holotype, KUMF.MOLL.1206 (NMR079), of Pinctada phuketensis sp. nov., showing shell shape and structures. Abbreviations: ad.m, adductor muscle scar; ant.a, anterior auricle; by.n, byssal notch; hl, hinge line; lig, ligament; na, nacreous; nn.b, non-nacreous border; post.a, posterior auricle; um, umbo. The shell is rather thin and small. The shell height, which does not exceed 80 mm, is slightly greater than the length (Figs 1 , 2 ). The shell convexity is moderate, with the left valve more convex than the right valve. The exterior surface of the shell (both valves) is typically dark greyish brown or green, crossed radially by alternating brownish black and lighter colored stripes. The non-nacreous margin has white porcelaneous patches, generally alternating with irregular, dark brown or black blotches and corresponding to the external coloration pattern. Growth processes on the outer surface of valves are small, flattened and brittle imbricating concentric scales which bear slender spines projecting radially towards the edge of the shell (Fig. 2 ). The posterior border is either small or absent from the posterior auricle. The dorsal margin is slightly curved and the umbonal area is low. Ridges on the back are high and obtuse, running from the umbo to the back end, with two faint secondary ridges (Fig. 2 ). The dark ligament is strong on the hinge line. Ligament is narrow, about 3/4 of hinge and elongation. The hinge line is straight, long and slightly shorter than the antero-posterior axis of the shell, with a ratio of 1:1.35 (Fig. 2 ). Hinge teeth are absent in the left valve and right valve (Fig. 2 ). The adductor muscle scar is kidney- or bean-shaped and clearly visible on the left valve. The right valve shows a larger attainment point scar on the shell. Scars on the back of the adductor muscle are very small. The anterior pedo-byssal retractor muscle scars are asymmetrical (Fig. 2 ). This structure is formed of individual byssal thread strands and extends ventrally and laterally from the base of the byssal groove to the short foot. For the soft body, the foot is a tongue-shaped organ located in the dorsal-anterior region of body, between the mouth and the byssus (Fig. 3A ). Byssus threads are dark green with thickened stalk (Fig. 3B ). Visceral mass is yellow and roughly half the size of its shell. It is ventral to the hinge and connected to the posterior adductor. The visceral mass contains digestive glands and gonad tissue. The heart is located posterior to the visceral mass, and consists of ventricle and auricles. Mantle margin is translucent dark, occupying most of the area between valves and extending from the hinge line (Fig. 3A ). The color of the mantle margin is dark, corresponding to the internal non-nacreous shell, which has blotches or streaks of dark pigment. The posterior adductor muscle is large, kidney- or bean-like in outline and located slightly posterior to the visceral mass and attached to each valve (Fig. 3A ). The posterior pedo-byssal retractor muscles are adjacent to the posterior adductor muscle and frequently inserted into its concave anterior border (Fig. 3A ). Figure 3. External view of the soft body parts of adult Pinctada phuketensis sp. nov. A and close-up view of overall of byssus B . Scale bars: 4 cm ( A ); 2 cm ( B ). Abbreviations: au, auricle; by, byssus; mm, mantle margin; pam, posterior adductor muscle; prm, posterior pedo-byssal retractor muscle; vm, visceral mass. Etymology. The specific epithet refers to the locality of Phuket Island, where this species was found. Phylogenetic analyses. Partial sequences of COI, 18S rDNA, ITS1, and ITS2 of recently collected Pinctada samples were successfully generated in this study. All sequences of P. phuketensis were identical for COI and 18S rDNA, and nearly identical for ITS1 (0.1-0.9% pairwise difference) and ITS2 (0.1-0.8% pairwise difference) but differed from sequences from other Pinctada species by at least 7% for COI, 0.2% for 18S rDNA, 2% for ITS1 and 1% for ITS2. The COI-based phylogenetic trees obtained by ML and BI analyses were topologically similar, and only the ML tree is shown (Fig. 4 ). The ML analyses indicated that all COI sequences of P. phuketensis sp. nov. formed a monophyletic group. Pinctada phuketensis sp. nov. was clearly phylogenetically distinguished from other species with high support (ML = 96%, BI = 1.00), and was sister to P. albina from Japan (Fig. 4 ). Figure 4. Maximum likelihood tree (-In L 4923.702) of partial COI sequences. Sequences of Pinctada specimens generated in this study are highlighted in bold. Support values are bootstrap/posterior probabilities. Asterisks indicate bootstrap (ML) value of 100% and posterior probability (BI) value of 1.00. Values <50% ML bootstrap and <0.90 posterior probability are not shown. GenBank accession numbers are given in parentheses. After the registration number or species name. Results of three species delimitation methods, namely GMYC model (blue column), bPTP (red column) and ASAP (yellow column), are indicated at the right edge of the tree. Additionally, phylogenetic analyses based on partial 18S rDNA sequences using ML and BI methods were highly congruent (Fig. 5 ). The ML tree supported the monophyly of P. phukentensis sp. nov., and a close relationship between P. phuketensis sp. nov. and two other Pinctada species, namely P. albina and P. nigra , with high bootstrap value (ML = 100%, BI = 1.00) (Fig. 5 ). Figure 5. Maximum likelihood tree (-In L 3134.144) of 18S rDNA sequences. Sequences of Pinctada specimens generated in this study are highlighted in bold. Support values are bootstrap/posterior probabilities. Asterisks indicate bootstrap (ML) value of 100% and posterior probability (BI) value of 1.00. Values <50% ML bootstrap and <0.90 posterior probability are not shown. GenBank accession numbers are given in parentheses after the registration number or species name. Similarly, the phylogenetic relationships constructed by ML and BI methods based on the concatenated ITS1 and ITS 2 data set showed very similar topologies (Fig. 6 ). All sequences of P. phukentensis sp. nov. formed a well-supported clade, and this clade was grouped with P. albina from Australia and P. nigra from China with high support (ML = 99%, BI = 1.00) (Fig. 6 ). Figure 6. Maximum likelihood tree (-In L 4787.958) of combined ITS 1 and ITS 2 sequences. Sequences of Pinctada specimens generated in this study are highlighted in bold. Support values are bootstrap/posterior probabilities. Asterisks indicate bootstrap (ML) value of 100% and posterior probability (BI) value of 1.00. Values <50% ML bootstrap and <0.90 posterior probability are not shown.