Vetigastropods are considered to be the most ancient, and primative, group of Snails. They are exclusively marine, but found in almost all marine environments, from the intertidal zones to the deepest abysal depths. Vetigastropods have nacrous (mother of pearl) shells, made from layers of aragonite platelets connected by protein fibres. This is thought to be the earliest form of shell to have appeared in Molluscs, with many groups of Molluscs separately evolving more durable solid calcite shells. Many Vetigastrolpods also retain breathing holes in their shells separate to the appatures from which the body extends, another trait considered to be primative in Gastropods (i.e. a trait seen in the earliest memers of the group, and subsequently lost in most members). Keyhole Limpets, Abalones, Top Shells and Turban Snails are Vetigastropods.
In a paper published in the journal Zootaxa on 21 January 2014, Renate Helwerda and Frank Wesselingh of the Naturalis Bidiversity Center in Leiden, The Netherlands, and Suzanne Williams of The Natural History Museum in London descibe three new species of fossil Vetigastropod Snail from the Plio-Pliestocene Santa Cruz Formation on Cabarruyan (or Anda) Island in the and around Tiep on neighbouring Luzon Island in the Philippines, as part of a wider study into Vetigastropod fossils at the area.
Map showing the locations on Cabarruyan where the majority of the specimens were obtained. Hewlwerda et al. (2014).
The first new species described is placed in the genus Halystina (a genus of small deepwater Snails known from the Pacific around the Philippines and New Caladonia), and given the specific name conoidea, meaning conical. Halystina conoidea is a 2.1 mm high, 1.7 mm wide Snail, with a ribbed shell, described from 34 specimens from Cabarruyan Island and one from Luzon.