The neogastropod family Melongenidae Fischer, 1884, is a relatively small, compact group of 22 recent and at least 42 post-Eocene fossil species and subspecies of medium-sized to very large predators. All species have a tropical to subtropical distribution in shallow waters, and all occur on the shores of continents and continental islands. In northwest Borneo the recent fauna is poor with three genera represented by one species each. In the Early Miocene three genera occurred with three species, in the Middle-Late Miocene three (possibly four) genera with six (possibly seven) species (Table 1). Three of these Miocene species are described as new species. A short introduction to the area and sampling performed is given in Raven (2002: 3-7).
Table 1. Melongenidae species and stratigraphic distribution based on records from northwest Borneo.
Although the taxonomic composition of pre-Oligocene members of this family remains unclear, the Oligocene to recent members appear to have ancestors among Late Eocene species of the genus Pugilina Schumacher, 1817. Most shells of the group are quite simple, but at least two phenotypes representing significant departures from the standard morphology have evolved, one of which may be unique within Gastropoda. Both of these phenotypes are known only from fossil melongenids in southeast Asia. In the course of a review of melongenid species from the Miocene of Borneo presented in this paper, we document these unusual phenotypes, one of which is associated with a new species and the other with both a new and a previously described Indonesian species. We place these odd morphologies into the broader context of evolution in the highly competitive environment of Neogene marine southeast Asia.
Abbreviations: coll., collection; Fm, Formation(s), fr., fragment(s); H, height; juv., juvenile(s); sp., specimen(s); W, width. For collections and legit: BM, Brunei Museum, Bandar Seri Begawan; BMNH, The Natural History Museum, London; BPM, Bataafsche Petroleum Maatschappij, The Hague, now Royal Dutch Shell; CL, Charlie Lee, Miri; GR, Gerard A. Raven, Leidschendam; MS, Mary Saul, Malvern; N, Novi E. Yusniasita Dols, Seria; PNHS, Panaga Natural History Society, Seria, Brunei; R, Han Raven, The Hague; RMNH, Nationaal Natuurhistorisch Museum (formerly Rijksmuseum voor Natuurlijke Historie), Leiden; RV, Ricardo Villar, Seria, Brunei; V, Jaap Vermeulen, Leiden; ZMA, Zoologisch Museum Amsterdam.
Material is recorded in the following order: COUNTRY, province, locality, geological formation, age, coll. number, number of specimens, leg., size.