Opinions and declarations Rendered by the International Commission on Zoological Nomenclature

Although regarded as conspecific, mature specimens (i.e. shells with a thickened outer lip) from the West Coast population are, however, noticeably smaller compared to the ones from Semakau (around 8.5-9 mm versus 9-11 mm in shell lengths). Both lots are identified as Mitrella essingtonensis; first based on Wilson (1994) then checked against the original description of the species by Reeve (1859). A prominent hump on the dorsal side of its body whorl distinguishes Mitrella essingtonensis from its congeners found in Singapore. The surface of the smooth and glossy shell is shrouded by a thin layer of periostracum. Shells of living specimens are often additionally covered with a layer of silt. Two distinct forms of Mitrella essingtonensis are present in Singapore. One with very dark ebony brown to nearly black shell and the other much paler brown (see accompanying picture). Both forms are common, but the dark form is seemingly predominant in the West Coast population. Curiously the form with brown spiral stripes on a very pale yellow to white shell, figured in Reeve (1859: pl. 27, fig. 174b) and Wilson (1994: pl.16, figs. 4A-4C), does not appear to occur in Singapore. Mitrella essingtonensis seems to be very common where it occurs (personal observations). Since the specimens from Semakau were previously listed as an unidentified species of Mitrella by Tan & Yeo (2010), Mitrella essingtonensis is herein regarded as a new record for Singapore.

These little nerites were determined to be Smaragdia souverbiana, a species which has not been previously recorded from Singapore (e.g., Tan & Clements, 2008; Sanpanich & Tan, 2016). Members of the genus Smaragdia are typically associated with seagrass, with the different species apparently preferring specific eagrasses (Rueda & Salas, 2007; Unabia, 2011; Rossini et al., 2014). Although they were seen only on Enhalus acoroides at Cyrene Reef, it would be premature to suggest that Smaragdia souverbiana has a preference for that particular species of seagrass. Prior to the present find at Cyrene, S. K. Tan has viewed images of a probable conspecific snail photographed on Halophila ovalis at Pulau Hantu in July 2017, by Destine Ang. As specimens were not available for detailed examination, the identitity of the Pulau Hantu snail could not beconfirmed. A study on an eastern Australian population of the same species by Rossini et al. (2014) suggests that they have a strong preference for Zostera capricorni; a seagrass that does not seem to occur in Singapore. Smaragdia souverbiana has been introduced and established in areas beyond its natural distribution since the late 1980s, particularly in the Mediterranean Sea (Zenetos et al., 2005; Rothman & Mienis, 2011). Its occurrence in Singapore is presumed to be natural because it is well within the known geographic range of this widely distributed Indo-West Pacific species (see Dekker, 2000; Eichhorst, 2016). Smaragdia souverbiana could have been overlooked in earlier studies due to its miniscule size, and future surveys with more focus on micro gastropods will likely reveal the presence of this species at more localities around Singapore.

This appears to be first record of Laeops guentheri in Singapore’s waters (see Fowler, 1938). The genus Laeops is characterised by having large eyes on the left side of the body; first ray of pelvic fin on eyed side on or near isthmus; upper jaw two times or greater in head length, not extending to rear edge of lower eye; all upper jaw teeth and nearly all, or all, lower jaw teeth confined to the blind side. Laeops guentheri is distinguished from its congeners in having its upper profile convex above and behind eye, body depth 2.5 to 3 times in standard length, and 76-83 anal fin rays. It is known to reach a total length of 14 cm, and has been taken at depths of 15 to 329 m, on sand-mud or sand-broken shell substrates, from Persian Gulf eastwards through Indonesia to the Gulf of Thailand (Hensley & Amaoka, 2001: 3835). The present record is unusual in that it was taken in an intertidal zone. Note: This is a contribution of the Singapore Comprehensive Marine Biodiversity Survey conducted by the National University of Singapore’s Tropical Marine Science Institute and the National Parks Board.

Pitar lineolatus is actually not exceedingly rare in Singapore, and the authors have previously encountered the occasional specimens around the Changi area. However, its occurrence in Singapore has apparently never been published before (e.g., Morris & Purchon, 1981; Tan & Woo, 2010). Hence, the present record is regarded as the first for Singapore.

The identities of the two snails were determined with reference to Wilson (1993), Okutani (2000), and Landau et al. (2014). Interestingly these two species do not seem to have been previously reported from Singapore (e.g., Tan & Woo, 2010; Sanpanich & Tan, 2016). The finds are thus regarded as the first records of these species from Singapore.

A new species of land snailis described from the Suan Hin Pha Ngam Limestone Area in Loei Province, northeastern Thailand. This species is placed in the genus Landouria Godwin-Austen, 1918 based on the presence of a slightly long club-shaped flagellum with variably sized tubercles, a gametolytic sac with swollen basal part, and absence of dart sacs and mucous glands. This is the first verified record of the genus Landouria in Thailand

The fish diversity in Punggol and Serangoon estuaries was documented before and after they were dammed to serve as reservoirs. A total of 119 species was recorded before the estuaries became landlocked. The fish community changed with the gradual conversion of the marine environment to freshwater. A year later, 32 species were recorded with seven additional freshwater species. This is a considerable drop in fish diversity as most species, unable to adapt to complete their life cycle in freshwater, disappeared. Their places were taken over by nine, largely alien, freshwater taxa.