Distribution and Morphological Assessment of the Genera Pincerna and Stomacosmethis (Gastropoda, Alycaeidae) from Selected Areas in Sarawak

• Main Author: Nur Izzati, Jeafree
• Format: Thesis
• Language: English; English; English
• Published: UNIMAS 2025
• Subjects: QL Zoology
• Online Access: http://ir.unimas.my/id/eprint/49558/

The genera of Pincerna and Stomacosmethis are a widely distributed genera in Sarawak. The shell variations within these two genera can be observed in certain morphological characters which required comprehensive study. Therefore, this research aimed to determine the extent of morphological variation of Pincerna and Stomacosmethis based on their shell characters. In this study, only one selected Pincerna species (P. globosa) and three species of Stomacosmethis (S. hosei, S. sadongensis and S. galbanus) can be found in Sarawak. A total of 283 adults P. globosa and 355 adults Stomacosmethis (S. hosei (280), S. sadongensis (42) and S. galbanus (33)) collected at limestone cluster in Bau, Padawan, Siburan, Niah and Miri. The collected specimens were deposited into Zoological Museum UNIMAS, Universiti Malaysia Sarawak. For shell shape analysis, geometric morphometric data was generated using landmarks with software tpsDig2 v. 1.1. For the shell size analysis, each shell was measured under stereo-microscope and colour images were captured using software Toupview. Seven measurements made were used to quantify shell size and shape: shell diameter (D), shell height (H), apertural width (AW), apertural height (AH), height of spire (SH) and width of spire (SW), and width of proto conch (PW) with scale 1 mm as guidance. Based on landmark analysis, there is a significant variation of shell shape of P. globosa (p < 0.0001) with respected to LM10, the highest point of the lip and LM15, the external point of the lip at the left profile of the shell. Principal component analysis based on geometric morphometrics show a total variation of 37.18% by the first two principal components. Furthermore, the populations from Padawan cluster shows the largest in terms of shell size when compared with populations from Bau and Siburan. While the genus S. hosei (p < 0.0001) shows the highest significant difference of LM13, the median lip point and the highest point of the lip (LM12). Principal component analysis based on geometric morphometrics show a total variation of 43.78% by the first two principal components. This study also discovered S. hosei from Bau cluster has the tallest shells. As a conclusion, there are significant variations of shell shape and size of Pincerna and Stomacosmethis from Sarawak. From this study, it shows that these species offer valuable ecological insights as they can adapt to diverse environment condition, serve as bioindicators and species identification which highlighting their importance in both ecological and conservation. These finding highlight the potential of these land snails to offer valuable ecological insights as they can adapt to diverse environment condition, serve as bioindicators and assist in species identification underscore their importance in both ecological and conservation efforts.