Unilocular calcareous benthic foraminifera from the deep-sea sediments of the Bay of Bengal

Benthic foraminifera, predominantly marine unicellular organisms, are abundant and diverse. Their tests with intricate and varied surface ornamentation make them unique and fascinating organisms. Among them, Unilocular calcareous benthic foraminifera have always been the least explored group due to their less frequent occurrence and small, fragile tests. Hence, a study on the unilocular foraminifera was conducted by collecting a core (4.15 m long deep-sea core of 12.7 cm diameter) sample from the deep-sea environment (3083 m depth) of the Bay of Bengal on the Research Vessel MGS Sagar. This study describes the vertical distribution of unilocular foraminifera, assesses their community structure, provides illustrated taxonomic descriptions and reports new records from the Indian waters. Twenty-five species belonging to seven genera, two families and one suborder were recorded, of which eight species are new reports from the Indian waters. The total abundance of the Unilocular foraminifera was 219 number/gram (9% of the total foraminifera abundance) Fissurina (77), Oolina (46) Parafissurina (28) and Lagena (28) were the most abundant genera. Vertical distribution of the unilocular species showed a decreasing trend with 19 species in the 0–100 cm to three species in the 301–415 cm of the core sample. Shannon Weiner diversity index (H’) values ranged between 0 and 3.75, with the highest of 3.75 recorded at the 138–140 cm layer. Pielou's species evenness (J’) values ranged from 0.82 to 1, and species dominance ranged from 0 to 0.5. Results of the analysis of similarity proved a significant variation in the species composition of unilocular benthic foraminifera between various depth layers of the core. Systematic descriptions of this taxa have also been included in the present study. This study is thus expected to fill the gap in knowledge of this lesser-known group of benthic foraminifera from the Indian waters.