Philyra malefactrix (formerly as Ebalia malefactrix or Nursia malefactrix) was first recorded from Singapore by Ow Yang (1963) from Pulau Senang. It has subsequently been recorded from East Coast, Kallang, Lim Chu Kang and Sungei Buloh (see: Tan & Ng, 1993, 1994; Chou et al., 1994; Rahayu & Ng, 2003; Wang & Ng, 2011). Specimens from Singapore agree well with the lectotype of this species selected and figured by Rahayu & Ng (2003). The present records are the first of this species from the Kranji area. The attached photograph is, to our knowledge, the first to be published of a Singapore specimen

The mangrove swamp-eel is very poorly known in Singapore, and appears to have been first mentioned as occurring there by Tan et al (2010: 143 as Opisternon [sic] bengalense) based on the 4.5 cm juvenile (ZRC 41645) from the Singapore River. Larger individuals can easily be mistaken for the Sunda swamp-eel (Monopterus javanensis) which it superficially resembles and with which it can co-occur (ZRC 51854 was taken with a Monopterus javanensis at Lower Seletar Reservoir).
With closer inspection, Ophisternon bengalense can be identified as follows: the eyes are located almost at the end of the head (Fig. 2), the origin of the dorsal fin is in front of the anus, and the gill opening is undivided and confluent gill membranes are free from the isthmus. In the Sunda swamp-eel (Monopterus javanensis), the eyes are located further away from the tip of the snout, the dorsal fin origin is behind the anus, and the confluent gill membranes are attached to the isthmus by a median septum that also divides the gill opening (Kottelat et al., 1993: 140; Rainboth, 1996: 177; Monopterus javanensis as Monopterus albus). The mangrove swamp-eel is known to have a preference for estuarine and tidal habitats (see Rainboth, 1996: 177). However, three of the eight specimens cited here were taken from freshwater. Examples from Lower Seletar Reservoir are likely to have descended from individuals trapped inland when the mouth of the Sungei Seletar was dammed from the Johor Strait around 1983 and 1984 (Quek et al., 2011: 60), and gradually adapted to freshwater. The single example from Lower Peirce Reservoir could have been taken there with water channeled from Lower Seletar or other coastal reservoirs.