Cerastuidae, Wenz, 1930

Jindal, Rajinder & Wats, Meenu, 2021, Systematic descriptions and seasonal variations of mollusc in Chandigarh (U. T., India) and its surrounding freshwater bodies, International Journal of Fisheries and Aquatic Studies 9 (3), pp. 165-173 : 170-171

Family: Cerastuidae

Cerastuidae is a family of air-breathing land snails. The shells of this family are ovate or oblong with size varying from small to medium. They are narrowly perforate or deeply umbilicate with fine sculpture or coarse striae.

Rachis punctatus (Anton, 1839)

Taxonomic description- Shell ovately conical, smooth, glossy; number of whorls 6, feebly convex to almost flattened; spire elevated, cone like; apex obtuse; aperture slightly oblique, ovate; outer lip sharp, columellar lip reflected.

3.4 Seasonal variations in molluscan fauna diversity Amongst the collected gastropod species Physa acuta was found ubiquitous and dominant species as well. In the hierarchy of dominance it was followed by Melanoides tuberculata , Gabbia travancorica , Filopaludina bengalensis typica and Filopaludina bengalensis mandiensis . The other species were found showing erratic occurrence and in lesser number. The species diversity, species richness and evenness of the collected molluscan fauna was found showing temporal or seasonal variations. ( Figure 2 ).

The site S1 was found inhabited by only three molluscan species and their maximum richness was observed in summer season (3 Sp.) followed by monsoon while the winter season witnessed the presence of a single species i.e. Physa acuta . In the post monsoon season no molluscan shell was recovered from this site. The maximum abundance was also observed in summer season (237) followed by monsoon (22) and winter (20). Despite of the maximum abundance and higher species richness in summer season, the values of Simpson’s Dominance Index (0.92) indicated the dominance of any one species.

The site S2 was found inhabited by only 4 species. The maximum species richness was observed in winter season (4 Sp.) followed by monsoon (3 Sp.), summer (2 Sp.) and post monsoon season (1 Sp.). Maximum abundance at this site was also observed in winter season (122) followed by monsoon (118), summer (77) and post monsoon season (1). In all seasons P. acuta was found as a dominating species.

From site S3, total 7 molluscan species were collected during the entire study period of two years. The maximum species richness was observed in summer season (6 Sp.) followed by winter (4 Sp.), post monsoon (4 Sp.) and monsoon season (2 Sp.). Maximum abundance was also recorded in summer season (468), followed by winter (389), monsoon (73) and post monsoon (30). Despite of the maximum species richness and abundance in summer season the value of Simpson’s Diversity Index (0.34) and H ̍ index (0.66) in summer indicated less diversity as compared to other seasons. This was due to the dominance shown by two species i.e. P. acuta and M. tuberculata while other species contributing towards the community diversity were represented in comparatively less number. Both the post monsoon and winter season witnessed equal number of species but the more abundance was observed in winter season in comparison to the post monsoon.

From site S4 three species i.e. P. acuta , M. tuberculata and G. truncatula were collected. P. acuta was found as a dominating species and was recovered in all four seasons. Only 2 specimens of M. tuberculata were collected in summer and winter season. A single shell of G. truncatula was found in summer season. P. acuta was found as a sole representative in monsoon and post monsoon season with 9 individuals in each season.

A total of 22 molluscan species were collected from the site S5. The summer and monsoon season were found supporting the maximum species richness (17 sp.) followed by winter (13 Sp.) and post monsoon (9 Sp.). Maximum abundance was observed during monsoon season (293) followed by summer (280), winter (239) and post monsoon (93). Though the monsoon season witnessed the maximum species richness and abundance still the values of Simpson’s Diversity Index (0.76) and H ̍ index (1.83) indicated less diversity as compared to other seasons. This was due to dominance shown by a few species. The same was supported by the higher values of Simpson’s Dominance Index (0.23) and lower values of Evenness Index (0.64) in the monsoon season. The other species were found in meager number hence were not contributing towards the species diversity. Similarly the summer season witnessed the maximum species diversity with highest values of Simpson’s Diversity Index (0.89), H ̍ index (2.42) and Evenness Index (0.85). The post monsoon season was found least favorable for the molluscan species to flourish and diversify.

The site S6 was found having very poor molluscan fauna with only two representatives i.e. Physa acuta and Galba truncatula . The maximum species richness was observed in winter season along with higher value of the Evenness Index (0.99) indicating the presence and equal distribution of both species followed by summer and monsoon season representing only single species ( P. acuta ), while no shell was found in the samples collected during the post monsoon season. The maximum abundance was observed in summer season (154) followed by winter (28) and monsoon season (12).

Figures

Fig 2: Seasonal changes in the diversity of molluscan fauna