121 NATURE IN SINGAPORE 2014 7: 121–127 Date of Publication: 14 October 2014 © National University of Singapore SINGAPORE MOLLUSCA: 8. THE FAMILY APLUSTRIDAE (GASTROPODA: HETEROBRANCHIA: ACTEONOIDEA) Siong Kiat Tan 1* , Martyn E. Y Low 1 , Leo H. S. Nguang and Chay Hoon Toh 1 1 Lee Kong Chian Natural History Museum, National University of Singapore 6 Science Drive 2, Singapore 117546, Republic of Singapore (*Corresponding author: nhmtsk@nus.edu.sg ) ABSTRACT. — The family Aplustridae, occurring in the waters of Singapore, is reviewed. The family is represented in Singapore waters by Hydatina albocincta and Hydatina zonata. Diagnoses, figures, records, and other information on both species are provided as part of an effort to document the diversity of the malacofauna in Singapore. KEY WORDS. — Mollusca, Hydatina, Singapore, taxonomy, synonyms, records INTRODUCTION In this instalment of a group-by-group treatments of the molluscs found in the Republic of Singapore (see Tan & Low, 2013, 2014; Ng et al., 2014), the family Aplustridae J. E. Gray, 1847, is reviewed. Hitherto two aplustrid species, Hydatina albocincta (van der Hoeven, 1839), and Hydatina zonata (Lightfoot, 1786), have been recorded. However, the presence of only Hydatina zonata could be confirmed by recent sightings and collections. Details of records in the literature, and notes of interest are included. The Aplustridae is a small family of sea slugs comprising about a dozen valid species found in the tropics worldwide. Its members bear a rather thin and generally ovate shell with a large aperture and a low or sunken spire. The living animals are colourful and flamboyant, and although the animals are relatively large, they are capable of withdrawing completely or almost completely into their shells. All species are predators that appear to feed exclusively on cirratulid polychaete worms, which are swallowed whole (Rudman, 1972; Gosliner et al., 2008). Secondarily derived toxins are also sequestered from their polychaete prey for their own protection (Gosliner et al., 2008). MATERIAL AND METHODS Records were collated from the available literature, and geographically-relevant material in various collections was examined. Primary synonyms and records mentioning Singapore are listed. Abbreviations of the collections from which specimens were examined in the course of this study are: ZRC = Zoological Reference Collection, Lee Kong Chian Natural History Museum (LKCNHM), National University of Singapore (NUS); TSK = collection of the first author; and CLN = collection of the third author. Measurements are given in the form of shell height (SH) × shell width (SW). Shell height is defined as the longest distance from the posterior (apical side) to the lowest part of the basal side of the peristome, and shell width is the distance between the edges of the widest part of the body whorl perpendicular to the coiling axis. All measurements are in millimetres (mm). Herein, the ‘International Code of Zoological Nomenclature’ is abbreviated as the Code (ICZN, 1999). SYSTEMATIC PART SUPERFAMILY ACTEONOIDEA D’ORBIGNY, 1843 Actaeoninae d’Orbigny, 1843: 106 (type genus Acteon Montfort, 1810). Remarks. — The family-group name Acteonoidea was first made available at the family-level (as Acteonidae) by d’Orbigny (1843: 106).