First record of Reticulammina cf. novazealandica (Xenophyophorea, Foraminifera) from the southern Andaman Sea, Indian Ocean

Jishnu, B K and Mohan, Smruthu and Viswambharan, Divya and Rohit, Prathibha and Nagasundaram, M (2026) First record of Reticulammina cf. novazealandica (Xenophyophorea, Foraminifera) from the southern Andaman Sea, Indian Ocean. Regional Studies in Marine Science, 102. pp. 1-8. ISSN 2352-4855

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Abstract

Remotely operated vehicle (ROV) surveys conducted during Geological Survey of India cruises SR-039 and SR-046 aboard RV Samudra Ratnakar documented the occurrence of giant agglutinated xenophyophores in the southern Andaman Sea, Indian Ocean. Seven xenophyophore individuals were observed from the West Sewell Rise (WSR) and Andaman Accretionary Prism (AAP) at depths ranging from 714 to 1586 m. Two specimens collected from the AAP at 1586 m were morphologically assigned to Reticulammina cf. novazealandica Tendal, 1972, based on test architecture and xenophyae composition. The specimens are characterized by a gray, highly friable, rounded to lumpy test composed of anastomosing lamella-like branches with circular to oval openings. Xenophyae consisted mainly of foraminiferal and radiolarian tests with fine sediment. SEM–EDX analysis of the dark binding matrix revealed aluminosilicate-rich material containing Fe- and S-bearing particles, suggesting the presence of Fe–S-bearing or metalliferous particles within the agglutinated test. However, because the examined specimens were dead, the possibility that these signatures partly reflect post-depositional diagenetic processes cannot be excluded. Although the observed morphology closely resembles published descriptions of R. novazealandica, molecular confirmation was not possible because the recovered material lacked visible cytoplasm. This study extends the known distribution of Reticulammina cf. novazealandica to the Indian Ocean, representing the first documented record of the genus from this ocean basin. The occurrence in polymetallic-nodule-bearing, tectonically active bathyal habitats underscores the need for systematic deep-sea biodiversity surveys across the under-explored bathyal zones of the Indian Ocean.

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