Vignadula kuraburiensis, Tan & Tan & Sanpanich & Duangdee & Ambarwati, 2022

Tan, Koh Siang, Tan, Samuel Hui Ming, Sanpanich, Kitithorn, Duangdee, Teerapong & Ambarwati, Reni, 2022, Xenostrobus or Vignadula (Bivalvia: Mytilidae)? A taxonomic re-evaluation of small black mussels inhabiting the upper intertidal zone of the estuaries of Southeast Asia, Zoological Journal of the Linnean Society 196, pp. 316-345 : 336-337

VIGNADULA KURABURIENSIS SP. NOV.

( FIGS 1–3 , 7 , 11 , 12C, D , 13 )

ZooBank registration.: urn: lsid: zoobank. org:act: F15E6689-04B3-43C6-B44E-7D98457FFB98

Diagnosis: Light brown to dark purple mytiliform shells with terminal umbones; anterior half of ventral region often golden yellow; animal without plicate gland; mantle edge at posterior region of animal bears ≤ 18 short, simple guard papillae.

Etymology: Named after the district of Kuraburi, Phang-nga Province in south-west Thailand, where the species was first collected. The gender of the genus Vignadula ( Kuroda & Habe, 1971) was not given explicitly in the original description, but is here assumed to be female because the species name of the type species was changed from atratus to atrata ( Kuroda et al., 1971: 348, 549).

Material examined: Holotype: PMBC 25290 , Ta Bon Bang Wan jetty south of the mouth of Baan Tang La Ong, Kuraburi District, Phang-nga Province, Thailand; SL = 12.8 mm (sequenced, XTSW1 ; Fig. 7A, B ) . Paratypes: PMBC 25291 , SL = 13.2 mm ( Fig. 7C, D ) ; ZRC.MOL.24068, SL = 12.3 mm (sequenced, XTSW3 ; Fig. 7E, F ) ; PMBC 25291 (sequenced, XTSW4 ) ; ZRC. MOL.24069, 24083 (intact individuals); Bang Ben Bay , Laem Son National Park, Ranong Province, Thailand , ZRC.MOL.24070 (sequenced, XTSW5 ), 24084 (intact individuals) .

Shell: Length ≤ 15 mm, thin, outline mytiliform; anterior region narrow, umbones terminal, barely separated from anteroventral extension; posterior region expanded, flat. Surface light brown to dark purple over dorsal region and posterior two-thirds of length of valves, anteroventral region golden yellow. Valve surfaces with fine, closely set commarginal lines that may be outlined in a darker colour. ‘Special byssal secretions’ (sensu Ockelmann, 1983; i.e. commarginal thickenings or serrations, presumably secreted by the foot) may be present. Umbones and anteroventral margin are in line. Prodissoconch II diameter ~210– 230 µm. Shell interior iridescent, usually reflecting the colour of the exterior; margins devoid of teeth. Ligament narrow, smooth without teeth; resilial pits absent.

Shell microstructure: Shell generally comprises two layers below the periostracum: a thin prismatic layer, under which a thick sheet nacreous layer is present. A thin, fibrous prismatic myostracum may be present within the sheet nacreous layer.

Anatomy: Up to 18 short, simple guard papillae along each side of inner mantle edge forming the inhalant aperture. Papillae translucent white, with opaque white subcutaneous pigment. Posterior byssal retractor muscles are split into two bundles (as observed on animal, although the muscle scars on the valves do not reflect this separation). Pericardium lies anterior to the posterior byssal retractor muscle complex (Category 2 of Morton, 2015a). Plicate organ absent. Foot yellowish white, vermiform. Labial palps vary in length according to shell size (see Theisen, 1982; Ockelmann, 1983), as does the number of folds (sorting ridges), which can range between 18 and 24 for SLs 10–13 mm ( Fig. 11 ).

Habitat: Mid- to high intertidal, amongst oysters ( Saccostrea Dollfus & Dautzenberg, 1920 ) on concrete pilings under jetty near mangroves.

Geographical distribution ( Fig. 13 ): So far, found only in Phang-nga and Ranong provinces along the Andaman Sea coast of Thailand.

Similar species: Owing to the inherent variability of shell outline and colour in V. atrata and V. mangle (see Figs 4–6 ), it is generally difficult to separate the new species from its congeners based solely on external appearance. However, in anatomical terms V. kuraburiensis is distinguished from V. mangle in having fewer folds on its labial palps (<20 folds in an animal ~ 12–14 mm SL; see Fig. 11 ) in comparison to the more numerous (> 30 folds) labial palp folds in V. mangle ( Table 1 ). In addition, the absence of a plicate organ (organ of Sabatier; Thomsen et al., 2018) at the base of the ctenidium in the new species also clearly distinguishes it from V. mangle . As for V. atrata , it is anatomically similar to V. kuraburiensis (i.e. small labial palps and absence of plicate glands), and although the two species are genetically distinct and do not overlap in geographical distribution, they cannot be separated reliably using external or internal morphology.

Figures

Figure 1. Concatenated four-gene Bayesian inference/maximum likelihood tree based on COI, ITS1, 28S D1R and H3 sequences of Xenostrobus mussels from East Asia and Australasia. Both 313 bp and full-length COI barcodes were used in the analysis. In several cases (e.g. SG X18 and SG X18-2; XTSW1 and XTSW1-2), two sequences from the same individual were incorporated into the analysis. For readability, some nodes on the branch tips have been omitted and the lengths of some branches truncated (marked by a double slash). Sequence codes with asterisks were obtained from specimens shown in Figures 4–7. Line and text colours correspond to the colour scheme used to differentiate the geographical distributions of the species represented in the clades A, B, C and D. Sequence code abbreviations: E Th, Gulf of Thailand; FJP, Fukuoka, Japan; GB, GenBank; HK, Hong Kong; Indon, Indonesia; J MY, Johor, Malaysia; JP, Japan; K EMY, Kuching, East Malaysia; K JP, Kagoshima, Japan; K TW, Kinmen, Taiwan; N JP, Nagasaki, Japan; P MY, Perak, Malaysia; SG, Singapore; S Indon, Surabaya, Indonesia; SW Th, south-west Thailand; Th, Thailand; Z Tan, Zanzibar, Tanzania.

Figure 2. Concatenated three-gene Bayesian inference/maximum likelihood tree based on COI, 28S D1R and H3 sequences of mussels from East Asia and Australasia, including additional sequences from GenBank. For readability, some nodes on the branch tips have been omitted and the lengths of some branches truncated (marked by a double slash). Sequence codes with asterisks were obtained from specimens shown in Figures 4–7. Line and text colours correspond to the colour scheme used to differentiate the geographical distributions of the species represented in the clades A, B, C and D.For an explanation of sequence code abbreviations, see legend to Figure 1.

Figure 3. Concatenated two-gene Bayesian inference/maximum likelihood tree based on COI and H3 sequences of mussels. For readability, some nodes on the branch tips have been omitted and the lengths of some branches truncated (marked by a double slash). Sequence codes with asterisks were obtained from specimens shown in Figures 4–7. Line and text colours correspond to the colour scheme used to differentiate the geographical distributions of the species represented in the clades A, B, C and D. For an explanation of sequence code abbreviations, see legend to Figure 1.

Figure 4. Vignadula atrata (Lischke, 1871). Sequenced specimens from Kyushu, Japan: A–H, Nagasaki; I–L, Kagoshima. A, B, XM NJ 0519; LV, SL = 11.2 mm (ZRC.MOL.24028). C, D, XNJ 0519A; LV, SL = 12.4 mm (ZRC.MOL.24029). E, F, XNJ 0519B; LV, SL = 10.6 mm (ZRC.MOL.24030). G, H, XNJ 0519C; LV, SL = 9.6 mm (ZRC.MOL.24031). I, J, XKJ 0519B; LV, SL = 8.0 mm (ZRC.MOL.24025). K, L, XKJ 0519C, SL = 6.6 mm (ZRC.MOL.24026). See also Clade C in Figures 1–3.

Figure 5. Vignadula mangle (Ockelmann, 1983) comb. nov. Selected sequenced specimens from Indonesia (A, B), Malaysia (C, D, I–L) and Singapore (E–H). A, B, X4I, Surabaya, E. Java; LV, SL = 9.9 mm (ZRC.MOL.24045). C, D, XA MYKS 1219A, Kampong Bako, Sarawak (Borneo); LV, SL = 12.8 mm (ZRC.MOL.24021). E, F, X8, Punggol Point; LV, SL = 10.1 mm (ZRC. MOL.24054). G, H, MX2, Sembawang Park; LV, SL = 14.8 mm (ZRC.MOL.24046). I, J, XAJ 12, Sungei Punggur, Johor (Malacca Strait); LV, SL= 6.8 mm (ZRC.MOL.24015). K, L, XMJ 3, Sungei Punggur, Johor (Malacca Strait); LV, SL = 10.9 mm (ZRC.MOL.24019). See also Clade D in Figures 1–3.

Figure 6. Vignadula mangle (Ockelmann, 1983) comb. nov. Selected sequenced specimens from Malaysia (A, B), Thailand (C–H) and Taiwan (I–L). A, B, XA MYPK 0419C, Lumut, Perak (Malacca Strait); RV, SL = 6.2 mm (ZRC.MOL.24041). C, D, XBT3, Pak Meng, Trang Province, Thailand (Andaman Sea); LV, SL = 11.9 mm (ZRC.MOL.24067). E, F, XTE6, Hua Hin, Prachuap Khiri Khan Province (Gulf of Thailand); LV, SL = 10.1 mm (ZRC.MOL.24004). G, H, XM TBB 0719C, Bangsaen Beach, Chonburi Province (Gulf ofThailand); LV,SL= 9.7 mm (ZRC.MOL.24007).I, J, XTW1, Kinmen,Taiwan; LV,SL = 9.2 mm (ZRC.MOL.24033). K, L, XTW6, Kinmen, Taiwan; LV, SL = 9.5 mm (ZRC.MOL.24038). See also Clade D in Figures 1–3.

Figure 7. Vignadula kuraburiensis sp. nov. Sequenced specimens from western Thailand: A–H, Ban Thung La Ong in Kuraburi District, Phang-nga Province; I, J, Bang Ben Bay, Laem Son National Park, Kapoe District, Ranong Province. A, B, XTSW1; LV, SL = 12.8 mm (holotype, PMBC 25290). C, D, XTSW2; LV, SL = 13.2 mm (paratype, PMBC 25291). E, F, XTSW3; LV, SL = 12.3 mm (paratype ZRC.MOL.24068). G, H, XTSW4; RV (anterior half of ventral edge partially broken), SL = 11.5 mm (ZRC.MOL.24069). I, J, XTSW5; LV, SL = 9.0 mm (ZRC.MOL.24070). See also Clade B in Figures 1–3.

Figure 11. Relationship between shell size and number of folds observed on the labial palps of four Vignadula species from East and Southeast Asia. Data from Ockelmann (1983) for Vignadula atrata, Vignadula balani and Vignadula mangle are indicated separately. Apart from data points based on the study by Ockelmann (1983) and three individuals of Vignadula kuraburiensis sp. nov., all are referable to genetically sequenced individuals based on this study.

Figure 12. Guard papillae of Vignadula (A–D) and Xenostrobus (E–G) species on the posterior region of the inner mantle margin attached to LV. All animals shown preserved in ethanol. A, Vignadula atrata, SL = 11.4 mm, Toishi-ko, Nagasaki, Japan. B, Vignadula mangle comb. nov., SL = 13.5 mm, Kampong Bako, Kuching, Sarawak. C, Vignadula kuraburiensis sp. nov., SL = 13.2 mm, Kuraburi, Phangnga, Thailand. D, V. kuraburiensis sp. nov., SL = 8.8 mm, Ban Baen, Ranong, Thailand. E, Xenostrobus inconstans, SL = 22.7 mm, Dunnalley Bay, Tasmania, Australia (TMAG E21829). F, Xenostrobus securis, SL = 24.8 mm, Swan River, Perth, WA,Australia. G, Xenostrobus pulex, SL = 13.1 mm, Cottesloe, Perth, WA, Australia. Scale bars: 1 mm in A–C, E–G; 500 µm in D.

Figure 13. Geographical distribution of Vignadula and Xenostrobus species in East Asia, Australia and New Zealand. Locations are based on examined museum material or material collected in the field for this study by the authors, and supplemented by information contained in papers by Colgan (2017: Xenostrobus securis); Colgan et al. (2020: Xenostrobus neozelanicus and X. securis); Horikoshi & Okamoto (2007: X. securis); Iwasaki (2013: X. securis); Iwasaki & Yamamoto (2014: X. securis); Kimura (1996: Vignadula atrata); Kimura et al. (1999: X. securis [?], as Xenostrobus sp.); Lee & Morton (1985: Vignadula mangle comb. nov., as Xenostrobus atratus); Lamarck (1819: X. securis [?], as Mytilus securis; MNHN-IM-2000-34894, three syntypes); Lutaenko et al. (2019: V. atrata); Morton (1999: Xenostrobus pulex); Morton (2004: Xenostrobus inconstans); Morton & Leung (2015: X.securis); Park et al. (2017: V. atrata);Wang et al. (2011: V.atrata); Wilson (1967: Xenostrobus spp.).