Magallana bilineata ( Röding, 1798 )

Tan, Koh Siang, , Siong Kiat Tan, , Sherralee S. Lukehurst, Wells, & Fred E., 2024, Assessing the threat of the oyster genus Magallana (Bivalvia: Ostreidae) in Singapore to the Australian marine environment, Raffles Bulletin of Zoology 72, pp. 162-183 : 175-176

Magallana bilineata ( Röding, 1798)

( Figs. 1, 2C, D, 4A–I, 6D–F, 7, 8)

Ostrea bilineata Röding, 1798: 170 (type locality: not stated).

Ostrea lugubris GB Sowerby II, 1871 (in 1870–1871): unnumbered caption page to pl., pl. 26, fig. 63 (type locality: “North America?”).

Ostrea iredalei Faustino, 1932: 546 , 547, pl. 1, figs. 1–4 (type locality: “ Navotas, Malabon, Parañaque, and other places on Manila Bay ”, Philippines).

Ostrea madrasensis Preston, 1916: 33–35 , figs. 11, 11a (type locality: “ Ennur backwater, Madras ”, India).

Published Singapore records.

Crassostrea lugubris – Ranson, 1967: 167, 168.

Magallana bilineata – Chan & Lau, 2022: 1, figs, 2–6 (Changi Beach).

Material examined. Singapore: 1 ex. (dry) ( ZRC.MOL.8582). Seletar , coll. Lim CF, 1964 ; 9 ex. (dry) ( ZRC.MOL.8611), 11 ex. (dry shells) ( ZRC.MOL.8613), 5 ex. (dry shells) ( ZRC.MOL.8615), Johor Strait, kelong no. E10, near Pulau Tekong, coll. Yang SL, 1986 ; 1 ex. (dry) ( ZRC.MOL.9714), Punggol Port , intertidal on rocks, coll. Lim CF, 10 September 2007 ; 1 ex. (dry) ( ZRC.MOL.8637), Sungei Serangoon , ex Lorong Halus charcoal warehouse, coll. Low MEY, 1 July 2010 ; 1 ex. (dry) ( ZRC.MOL.26389), off Northeast Pulau Tekong , floating oyster farm, coll. Tan SK, 28 February 2011 ; 2 ex. (dry) ( ZRC.MOL.8635), 1 ex. (dry) ( ZRC. MOL.27070), Pulau Semakau , Phase II lagoon, coll. Tan SK, 2–3 March 2011 ; 2 ex. (dry) ( ZRC.MOL.28669), Pulau Ketam , mangroves, coll. Lai JCY, 23 November 2011 ; 6 ex. (dry & wet) ( ZRC.MOL.27255), Pulau Semakau , Phase II, coll. Tan SK et al., 23 August 2012 ; 2 ex. (dry & wet) ( ZRC.MOL.28476), Lazarus Island , coll. Lee BY et al., 9 August 2019 ; 1 ex. (wet) ( ZRC.MOL.27254), Khatib Bongsu , attached on plastic barrel in mangroves, coll. Tan SK, 16 September 2019 ; 1 ex. (dry) ( ZRC.MOL.24730), Sentosa , Tanjong Rimau, coll. Tan HH et al., 12–16 July 2021 ; 1 ex. (dry) ( ZRC.MOL.26393), western bank of Sungei Pandan, near Singapore Rowing Association , ca. 01°18′28.3″N 103°45′02.3″E, coll. Tan HH et al., 4 May 2022 ; 1 ex. (wet) ( ZRC.MOL.26224), western bank of Sungei Pandan , ca. 01°18′35.5″N 103°44′47.7″E, coll. Tan HH et al., 5 May 2022 ; 2 ex. (dry) ( ZRC.MOL.26234), 4 ex. (wet) ( ZRC.MOL.26260), western bank of Sungei Pandan , ca. 01°18′28.1″N 103°44″46.8″E, coll. Tan HH et al., 5 May 2022 ; 7 ex. (wet) ( ZRC.MOL.26150), 1 ex. (dry) ( ZRC. MOL.26339), eastern bank of Sungei Pandan , near tidal gates, ca. 01°18′38.1″N 103°44′52.5″E, coll. Tan HH et al., 13 May 2022 ; 1 ex. (dry & wet) ( ZRC.MOL.27660 [DNA #SG 25]), 6 ex. (wet) ( ZRC.MOL.27730), Pulau Tekukor , N1°13.787′ E103°50.260′, jetty piling, coll. Tan KS et al., 20 February 2023 ; 7 ex. (dry & wet) ( ZRC.MOL.27661), Lazarus Island-Pulau Seringat , N1°13.652′ E103°51.042′, vertical seawall, coll. Tan KS et al., 20 February 2023 ; 2 ex. (dry & wet) ( ZRC.MOL.27662 [DNA #SG 14), 1 ex. (dry & wet) ( ZRC.MOL.27663 [DNA #SG 15]), 1 ex. (dry) ( ZRC. MOL.27664), St John’s Island , N1°13.238′ E103°51.024′, mangroves, coll. Tan KS et al., 20 February 2023 ; 1 ex. (dry & wet) ( ZRC.MOL.27665 [DNA #SG 56]), East Coast Park , Fort Road canal, N1°17.659′ E103°53.440′, concrete sloping wall, coll. Tan KS et al., 22 February 2023 ; 1 ex. (dry & wet) ( ZRC.MOL.27666 [DNA #SG 41]), 1 ex. (dry & wet) ( ZRC.MOL.27667 [DNA #SG 42]), 3 ex. (dry & wet) ( ZRC. MOL.27668), East Coast Park , N1°18.346′ E103°55.756′, Siglap Canal, on sloping canal wall, coll. Tan KS et al., 22 February 2023 ; 1 ex. (dry & wet) ( ZRC.MOL.27670 [DNA #SG 67]), 1 ex. (dry & wet) ( ZRC.MOL.27671), Changi Creek mouth, N1°23.483′ E103°59.292′, on sloping granite wall, coll. Tan KS et al., 23 February 2023 ; 1 ex. (dry & wet) ( ZRC.MOL.27673 [DNA #SG 59]), 1 ex. (dry & wet) ( ZRC.MOL.27674 [DNA #SG 60]), 1 ex. (dry & wet) ( ZRC.MOL.27675 [DNA #SG 61]), 1 ex. (dry & wet) ( ZRC.MOL.27676 [DNA #SG 62]), 3 ex. (wet) ( ZRC. MOL.27731), Punggol Point , N1°25.300′ E103°54.639′, rocks on beach, coll. Tan KS et al., 23 February 2023 ; 1 ex. (dry & wet) ( ZRC.MOL.27677 [DNA #SG 73]), 1 ex. (dry & wet) ( ZRC.MOL.27678 [DNA #SG 71]), 1 ex. (dry & wet) ( ZRC.MOL.27679 [DNA #SG 72]), 4 ex. (dry & wet) ( ZRC.MOL.27680), Sungei Simpang Kiri , N1°27.380′ E103°50.448, on sloping concrete canal wall, coll. Tan KS et al., 24 February 2023 ; 1 ex. (dry & wet) ( ZRC.MOL.27681 [DNA #SG 84]) , Republic of Singapore Yacht Club , N1°17.651′ E103°45.595′, coll. Tan KS et al., 24 February 2023 .

Description. Shell: Valves large (SL commonly around 7 to 10 cm, largest examined SL 15.6 cm [LV]), generally quite circular or ovate in outline, often becoming more dorsoventrally elongated in larger specimens. External surface of RV dark yellow to purplish or greyish brown, often with irregular blotches and/or one or more darker radiating bands or numerous fine streaks, with overlapping thin, flaky foliose commarginal edges. Interior surface of valves generally white with a slight pearly sheen, with or without varying degrees of discoloured pink and greenish patches or purplish brown blotches that may become dominant in some specimens, and often with white calcareous patches. Interior margin of RV often with narrow yellowish-brown border that is broadest ventrally. Umbonal cavity of LV usually shallow, sometimes absent or indistinguishable. The kidney-shaped adductor muscle scar is brownish grey to nearly black, usually similar in colouration in both valves, but may occasionally be darker in one valve than the other.

Body. Living animals with mantle edges coloured brown to dark brown; visceral mass yellowish brown. Mantle edge outermost layer smooth, tentacles absent; outside wall not pigmented, inside wall with faint black surface pigment. Mantle edge middle layer with tentacles along entire edge; tentacles are variable in size, with larger tentacles slightly offset from edge and originates from side of wall facing the innermost layer. Outside wall of middle layer not pigmented, while the inside wall is heavily pigmented black. Mantle edge innermost layer with black dimorphic tentacles that become smaller, spaced farther apart and less black dorsally. Mantle surface colouration over visceral mass dark yellow to brown.

Habitat. On bark of mangrove trees, intertidal jetty pilings and seawalls, as well as on sloping walls of tidal canals.

Remarks. This large species has often been referred to as the junior subjective synonym Crassostrea iredalei (now M. iredalei ) in oyster aquaculture literature (e.g., Poutiers, 1998). The contrasting dark muscle scar colouration against the otherwise white interior is characteristic and appears to be reliable for distinguishing this species from M. belcheri . Its wide distribution in Singapore suggests it can tolerate a wide range of salinities. The species is also commonly cultured in Southeast Asia, including Malaysia (e.g., Tan & Wong, 1996; Abidin et al., 2016), Philippines ( Lebata-Ramos et al., 2021), Thailand ( Klinbunga et al., 2005; Bussarawit et al., 2010, as C. iredalei ), and Vietnam ( Vu et al., 2017, as C. madrasensis ).