Staircase Snails, Diplommatinidae, are small terrestrial Gastropods with operculi, which get their common name from the strong ribbing on their shells, which can resemble a spiral staircase. They are members of the Cyclophoroidea, a group of Caenogastropods which have lost their combed gills and developed an internal lung independently of the Pulmonata.
In a paper published in the journal Folia Malacologia, Jaap Vermeulen of JK Art and Science and Mohd Zacaery Khalik of the Faculty of Resource Science and Technology at Universiti Malaysia Sarawak, describe five new species of Staircase Snails from Borneo.
The first new species described is placed in the genus Arinia, and given the specific name bathyodon, meaning 'deep-tooth'. The species is described from a collection of shells gathered on a limestone plateau in a primary rainforest Sangkulirang Peninsula in the Indonesian province of Kalimantan. These shells are 1.2-1.6 mm high, 0.75-0.90 mm wide, and ellipsoid-cylindrical to almost cylindrical in shape, with the last two whorls widest in frontal view. The whorls are convex, and there is a constriction of the shell before the aperture, which lacks teeth. The radial ribs are single-crested, and there are 8-12 per 0.5 mm.
The second new species is also placed within the genus Arinia, and given the specific name congener, meaning 'of the same kind', in reference to the fact that it closely resembles the previously described Arinia similis, which is found in the same area. The species is described from a series of shells collected in the Gunung Mulu National Park in Sarawak Province, Borneo, on the path between Clearwater Cave and Moonmilk Cave. These shells are 1.0-1.2 mm in height, 0.75-0.80 mm in width, and shortly ellipsoid-cylindrical in shape, with the body whorl or last two whorls widest in frontal view. There is a constriction before the aperture, which lacks teeth. The earlier parts of the shell have 12-17 ribs per 0.5 mm, which drops to 5-7 ribs per 0.5 mm after the second half of penultimate whorl.
The third new species is again placed in the genus Arinia, and given the specific name semiconica, meaning 'half-cone-shaped', in reference to the shape of the shells. The species is described from a series of specimens collected at Kampong Air Putih near Samarinda, and at Gua Ambulabung in the Baay river valley on the Sangkulirang peninsula, with both localities being in Kalimantan. These shells are 1.7-2.3 mm high, 1.45-1.70 mm wide, and conical with almost flat sides, with the body whorl widest in frontal view. The whorls are convex, with the body whorl often slightly more narrowly rounded at the periphery. A constriction is present before the aperture, which lacks teeth. The ribs are single-crested with 3-6 ribs per 0.5 mm.
The fourth new species is placed in the genus Notharinia, and given the specific name xenos, meaning 'foreigner', in reference to the fact that the genus Notharinia has previously only been identified from Laos and Cambodia, locations significantly distant from Borneo. Vermeulen and Khalik note that the genus Notharinia is similar to the genus Arinia, differing mainly in the constriction of the shell before the aperture of adult shells of Arinia, which is absent in Notharinia; something which could potentially have been lost separately in Notharinia xenos, thereby making the genus paraphyletic, but in the absence of genetic data they choose to base their diagnosis upon the available morphological data.
Notharinia xenos is described from six shells collected from limestone scarps in the upper Tatau river valley of Sarawak State Malaysia. These are 1.9-2.4 mm high and 0.85-0.90 mm wide, with cylindrical shells, slightly widened towards the base. The whorls are moderately convex, the ribs single crested and there are 8-15 ribs per 0.5 mm.
The final new species is placed in the genus Opisthostoma, and given the specific name hemituba, meaning 'half-trumpet' in reference to the shortened shells of this species. The species is described from a series of shells collected at Gua Mardua near Kampong Pengadan on the Sangkulirang Peninsula of Kalimantan Province, Indonesia. These range from 1.6 mm to 1.7 mm in height and from 1.60 mm to 1.75 mm in width, and are shortly cylindrical to depressed conical, with the body whorl widest in frontal view. The apex of the shell is oblique and truncated. The whorls are moderately convex, and rounded, the body whorl is rather narrowly rounded at the base, towards a constriction before the aperture. The ribs are low and thin, being widely spaced; on the spire there are 3-5 ribs per 0.5 mm, on the body whorl this drops to 2-3 ribs per 0.5 mm.
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