SERMYLA RIQUETII (GRATELOUPE, 1840)

(FIGS 1 A–O, 4, 11C, D)

Melania riquetii Grateloupe, 1840: 433, pl. 3, fig. 28.

Type locality: ‘Bombay’ (Mumbai, India) in the original publication, but ‘Batavia [1. line], Samarang [2. line]’ (Jakarta, Semarang, Java, Indonesia) on the label of the type series (BMNH 1907.11.2240–1; see also Glaubrecht et al., 2009).

Melania harpula Dunker, 1844 in Philippi (1844: 161, Melania pl. 3, fig. 6).

Type locality: ‘ Java?’ (Java, Indonesia) in the original publication, but ‘ Philippinen’ (Philippines) on the label of the type series (ZMB 109669).

Melania mitra Dunker, 1844 in Philippi (1844: 162, Melania pl. 3, fig. 9).

Type locality: Not given in the original publication, but ‘ Philippinen’ (Philippines) is mentioned on the label of the type series (ZMB 109670).

Melania semicostata Philippi (1847: 171–172, Melania pl. 4, fig. 12) (non Melania semicostata Conrad, 1835).

Type locality: ‘Java’ (Java, Indonesia).

Melania tornatella Lea & Lea, 1851: 185–186 .

Type locality: Shallow rivers, Tanhay, Isle of Negros, Philippines.

Melania sculpta Souleyet, 1852: 546, pl. 31, figs 16–18.

Type locality: ‘ Îles Philippines’ (Philippines).

Sermyla kowloonensis Chen, 1943: 20, pl. 6, fig. 3. Type locality: Kowloon, on the mainland opposite Hong Kong.

Type material: Melania riquetii: two syntypes (BMNH 1907.11.2240–41). Melania harpula: one syntype (ZMB 109669). Melania mitra: two syntypes (ZMB 109770). Melania tornatella: three syntypes (BMNH 1978155). Melania sculpta: lectotype (present designation; BMNH 1854.7.24.381) ; five paralectotypes (BMNH 1854.7.24.381; only one conspecific with the lectotype, see Fig. 1 G and Remarks below). Sermyla kowloonensis: Holotype (USNM 48041)

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Additional material examined: Samples indicated by ‘w’ refer to ethanol-preserved material used for molecular genetic analyses herein. India: (MCZ; USNM 41037, 119780); Bombay (MNHN); Malabar Coast (MNHN) ; Guilon (USNM 515619) . Sri Lanka: (MCZ; USNM 20005) . Thailand: (MCZ 292173 w); Narativat, canal of the Lagoon (MCZ 292170; SMF 21987-1; ZSM 3817 w); Klong Koto, 40 km from Narativath to Pattani (ZSM 3818); Pak Panang near Nakon Sri-Tammarath (MCZ 288662, 292172; SMF 219868–9; ZSM 3812 w; MNHN); Kao Yoi, near Petburi (MCZ 288656; SMF 219861 /1, 244575/10, 271681/45; ZSM 624); Ban La Mung, Chonburi Province, Klong Na Glua at Ban Na Glua (MCZ 256624, 292171 w, 280588; SMF 219858–60; ZSM 621–2 w) ; Klong Na Chom Tian, Chonburi (SMF 206921 /6; USNM 776183, w) ; Pattaya, Mung (SMF 219859); Pattaya, Na Klua (SMF 219857); Maenam Chao Phraya, Bangkok (SMF 219862, 220341 /15; ZSM 3811 w); Klong Ka Seng, Smgkla (SMF 198239 /9); Ko Samui: Klong Jokare, Ang Tong (SMF 219863–4; USNM 776209 w, 794130 w); Ban Had Lamai (SMF 219866); Ban Bo Phud (SMF 219865 /15); Klong Lung Wat Thai, near Pak Bang, Ratapun (ZSM 3839 w); Gulf of Siam, Koh Pa-ngan (USNM 384123, 384126); Ban Amphoe, Sattahieb (USNM 776740, w); Klong La Mung, Chonburi (USNM 777539) ; Puek Tian, N of Hua Hin, 12°57.495´N 100°1.91´E (ZMB 107883, 107886) ; Petchaburi, drainage near Puek Tian, 12°57.426´N 100°2.075´E (ZMB 127817); Samut Song Khram, Don Hoi Lot, 13°22.084´N 100°0.267´E (ZMB 127818) . Vietnam: (MCZ); Tonkin: Phong Tho (?) (ZMB 61228) ; Tuan Chau Island, Ha Long Bay (BMNH 2403) ; Hue, Laggon near Lang Co, 16°15.67´N 108°3.52´E, (ZMB 114421) . China: (USNM 195903); Hongkong (CAS 6164; MCZ 167009; SMF 50022/8, 39143-a/1, 39143/27, 39144, 115456/18, 291774/6, 213472/3; ZMB 94721); Landau, near Hongkong (SMF 39146/10) ; Kowloon (USNM 516422–3); Macau (SMF 39147/3, USNM 218446); Setshuan (SMF 291775 /6); Hainan (SMF 39142, 39145 /6, 39148/2, 39161/39, 291773/5) . Japan: Riu Kiu Islands: Okinawa (USNM 342622) ; Loochoo Islands: (MCZ 43018) ; Naha (USNM 218541) . Philippines: (CAS 6216; MCZ 74828, 49684; MNHN; SMF 291786–7, 291790/2; ZMB 26735, 210087); Ubay (BMNH) . Leyte: estuary, 2 miles S of Tanauan, W side of airfield (MCZ 179067; USNM 788823) ; Ormoe Bay (MCZ) ; Tarragona, 1 mile E (MCZ) ; Baybay (USNM 788745); Cancabato River, bridge at Burayan (USNM 789949) ; Lubang Island: (USNM 467359) ; Cabuyan Islands, SW of Lubang (MCZ 138214) ; Loac, Agkawayan River (MCZ 108214) ; Cabra Island (MCZ 138202) . Luzon: Manila (MCZ 22245; USNM 259116, 654082); Pasigfluss (ZMB 210084); near mouth Sayabas River (USNM 239995) ; Camp Wallace, La Union (USNM 259258); Basiguran (USNM 259228); Bacoon Bay (USNM 259361, 258891) ; Port San Vincente, Palaui (USNM 259014) ; Bin Malay, Pangasinan (USNM 608320); Merivales Harbor (CAS 20691) . Negros: (USNM 118539, 130784); Dunagusta (USNM 881), Guijulugan (USNM 243523) . Mindoro: Sapa, Lubang (MCZ) ; Malugayo River (USNM 258966) ; Naujan River (USNM 259340) ; Paluan Bay, mouth of Paluan River (USNM 239849, 258940) , Caminiwit Pt. (USNM 487579, 487592) . Mindanao: Dapitan (MCZ 22244; SMF 291789 /9); Minlagas, Misamis (SMF 291791 /1); Opol (USNM 258972); Santa Cruz: Davao (MCZ 36265) ; Davao River (USNM 258907, 259317, 739431); near Zamboanga (USNM 259128, 591910); Susigao River (USNM 258922, 544066) ; S of Cotobata (USNM 258953) ; Malaling River, Malabang (USNM 259296, 258984) . Palawan: Iwahig River, near Alf (CAS 599) ; Siquijor (SMF 291788 /17); Bagac, Bataan (USNM 774990, 775021) . Singapore: (ZMB 210077); Bedok Well (USNM 622515); Mandai River estuary, N Singapore, 1°26´N, 103°46´E (AMS C.317335) . Indonesia: Java: (MNHN, ZMB 210080); ‘ Batavia’ (= Jakarta) (ZMB 107007); Batavia, rice fields (MCZ 90663) ; West Java, Ujungkulon Peninsula, Nyiur (CAS 109940 w); Sukabumi (ZMB 210078); Garoet (MCZ 115025) . Borneo: Balikpapan (MCZ 100483), Singkawang (ZMB 210083) . Bali: Gumbrih River, 8°26.542´S 114° 52.598´E (ZMB 106474) ; Lovina (ZMB 104180); Lombok: SW Pemenang, near estuary (ZMB 104178); Laboean Hadji, beach (ZMB 75506) . Sumbawa: Satonda Island, crater lake (ZMB 104179) . Flores: Waiara, E of Maumere, 8 °38.391´S 122 °18.707´E, (ZMB 106473) . Timor: Kupang (210085). Banka: Muntok (ZMB 210081) . Bunguran: Sungei Illu (ZMB 210086) . Bismarck Archipelago: New Britain: Karlei, Weite Bucht (ZMB 87303) ; Weite Bucht (ZMB 87305) ; Malkong (ZMB 87304) ; Willaumez-Halbinsel: Nakanai ( Dakatansee) (ZMB 87362) . New Ireland: E coast, Medina, 100 km S Karieng (USNM 858220 w) . Solomon Islands: Bougainville Id., Kieta (MCZ 111918); Guadalcanal, Lunga River (USNM 610202) .

Diagnosis: Shell less than 20 mm high, aperture approximately as high as the spire; opisthocyrt ribs and basal spiral grooves well-developed. Crawling juveniles released from subhaemocoelic brood pouch of female.

Description

Shell (Fig. 1A–O): Shell compact, oval, usually dark brown (sometimes lighter brown or cream coloured with darker spots) with up to seven whorls; up to 20 mm high. Sculpture on body whorl and spire prominent axial, opisthocyrt ribs; on basal part of body whorl also with elevated spiral ridges and deep spiral grooves.

Reproduction: Brood pouches of females filled with about 25 to 80 (mean 64) shelled juveniles of different ontogenetic stages, i.e. reproductive strategy euviviparous.

Juvenile shell (Fig. 5B): Juvenile shells with up to five whorls and pronounced axial ribs, crossed by more or less developed spiral ridges. Most of the juveniles ~ 1 mm high (maximum 2.5 mm). Percentage of juveniles bigger than 1.1 mm ranges from 2.5% (Bali) to 12.8% (Thailand).

Radula (Fig. 11C, D): Taeniogloss and typical for Thiaridae (see: Glaubrecht et al., 2009). Rachidian with a narrow triangular central denticle with a sharply pointed tip and three smaller denticles on either side of central denticle, also triangular in shape with a sharply pointed tip. Central denticles of the lateralia broad and rounded, flanked by two to three pointed denticles on either side. Marginal teeth with six to seven denticles.

Ecology: Sermyla riquetii was originally suspected to be a marine species by Grateloupe (1840: 433: ‘Je la soupconne marine’). This is erroneous insofar as we found all Sermyla species in freshwater to brackishwater environments in the estuaries of tropical streams, above the influence of the tides, where it lives on muddy and sandy substrate and feeds on detritus. Based on our observation from sampling in Thailand, S. riquetii was found in the quieter regions of the river rather than in the running stream, because in those parts mud, sand and richer substrate can accumulate.

Distribution: The species is distributed from India and Sri Lanka into the mainland and insular regions of Southeast Asia, the Indo-Malay Archipelago ranging far into the Pacific region and to Australia (see Fig. 2 and the material list for details).

Remarks

All samples collected outside of Sulawesi and Australia belong to S. riquetii as here delimited. Accordingly, we synonymize M. harpula, M. mitra, M. semicostata, M. tornatella, M. sculpta and S. kowloonensis with S. riquetii, which exhibit no discernible differences that would justify species separation. The type series of M. sculpta includes at least three different thiarid species. To stabilize the name, we here select the specimen shown in Figure 1G as the lectotype of M. sculpta . There is one paralectotype considered here to be conspecific with the lectotype. One of the remaining four paralectotypes is identified as Mieniplotia scabra (Müller, 1774) . The other three probably belong to the taxonomic complex comprised by the genus-group taxa Melanoides Olivier, 1804, Stenomelania Fischer, 1885 and Neoradina Brandt, 1974 in the sense of Wiggering et al. (2019).

Glaubrecht et al. (2009) supposed an ovoviviparous reproductive strategy for S. riquetii based on the investigation of material from Sulawesi. However, our results suggest that this particular reproductive strategy is actually restricted to samples from Sulawesi only, which we here suggest to represent a distinct species (see below). In contrast, S. riquetii has an euviviparous reproductive strategy, which we recorded here for samples from Thailand, Vietnam and Bali, and which Bandel & Riedel (1998) recorded for samples from Negros Island (Philippines). However, it has to be noted that this hypothesis should be tested when additional preserved material becomes available for study in the future.