We describe, illustrate and give geographical information on 40 diatom species observed in two short sediment cores from a Holocene deposit in the Indian Sundarbans region. The Indian Sundarbans is an extremely vulnerable ecosystem that is sensitive to palaeoclimatic change. The cores were originally collected for palaeoecological reconstruction based on the analysis of diatom assemblages. The research presented here is the first step in the analysis of the subfossil diatom assemblages, which will rely heavily upon correct taxonomic identification, and is the first study of diatoms from sediment cores in this ecosystem. The present study documents 40 diatom species; 38 are new to this region. The descriptions include 11 centric species belonging to eight genera and 29 pennate species belonging to 17 genera in total. The centric diatom, Thalassiosira was the most abundant genera represented by three different species. Thalassiosira nanolineata was rarely found in the sediment from one core and not observed in the other. Tryblionella and Nitzschia were the most abundant pennate diatoms, represented by four different species each in one of the sediment cores. Diatoma moniliformis, Pseudostaurosira brevistriata, Geissleria decussis, Neidium affine, Cosmioneis pusilla, Trachyneis antillarum, Petroneis granulata and Tryblionella punctata were much less abundant species in the studied cores samples. Literature studies show that apart from two species, Actinoptychus annulatus and Thalssiosira eccentrica, 38 species have never been reported from the plankton and have also not been found previously in surface sediments of the Indian Sundarbans region. Annotated lists of the identified diatoms have been prepared along with high quality microphotographs as part of the preliminary work that will be necessary for ongoing palaeoecological reconstruction.

中文翻译：

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在短沉积岩芯中发现印度孙德尔本斯的新硅藻类群

我们描述、说明并提供了在印度孙德尔本斯地区全新世矿床的两个短沉积岩芯中观察到的 40 种硅藻的地理信息。印度孙德尔本斯是一个极其脆弱的生态系统，对古气候变化很敏感。这些岩心最初是基于对硅藻组合的分析收集的，用于古生态重建。这里介绍的研究是亚化石硅藻组合分析的第一步，这将在很大程度上依赖于正确的分类学鉴定，并且是对该生态系统中沉积物核心硅藻的首次研究。本研究记录了 40 种硅藻；38 是该地区的新成员。描述包括属于8属的11个中心种和属于17个属的29个羽状种。以硅藻为中心，Thalassiosira 是由三个不同物种代表的最丰富的属。Thalassiosira nanolineata 很少在一个岩心的沉积物中发现，而在另一个岩心中没有观察到。Tryblionella 和 Nitzschia 是最丰富的羽状硅藻，在沉积物核心之一中分别由四种不同的物种代表。在研究的岩心样品中，念珠状硅藻、短尾假单胞菌、Geissleria decussis、Neidium affine、Cosmioneis pusilla、Trachyneis antillarum、Petroneis granulata 和Tryblionella punctata 的种类要少得多。文献研究表明，除Actinoptychus annulatus 和Thalssiosira eccentrica 2 种外，还有38 种从未在浮游生物中报道过，之前在印度孙德尔本斯地区的表层沉积物中也未发现过。