First report of the rare tintinnid genus Stelidiella Kofoid and Campbell 1929 in the Indian Ocean

Abstract

This study provides detailed information on the morphometry and distribution of some rare tintinnids species found in the Indian Ocean. The morphological features (scabbard-shaped with a fenestrated collar) reported here resemble those of the genus Stelidiella. Here, lorica morphology (fenestra arrangement and oral margin (OM) pattern) was the sole criteria for Stelidiella species identification. The dimensions and morphology (presence of two layers of fenestrae rings with smooth OMs) resemble the original description of Stelidiella fenestrata, a warm-water species. We found both small (260 ?m long) and large S. fenestrata (309 ?m long) with smaller and larger bowls in the former and latter, respectively. In the Indian Ocean, S. fenestrata was more abundant (i) between 12oN and 18oS (particularly, central Indian Ocean) similar to that reported in the Pacific Ocean; (ii) in the mesopelagic zone (100-1000 m) than the epipelagic zone (0-100 m) and (iii) in the winter season of December 2021-January 2022 than in spring inter-monsoon of March-May 2021. The S. fenestrata, despite being in low abundance (2-26 individuals 10 m?3), is widespread in the region, and their role in the ecosystem merits further investigation.