First record of Ditrupa gracillima (Annelida, Polychaeta) from the late Pliocene of Andaman and Nicobar Basin: insights on the ultrastructure, stable isotopic signature and distribution pattern

In the present study from the late Pliocene of Neill West Coast Formation, Neil Island, serpulid tubes assignable to Ditrupa gracillima Grube have been identified with the help of tube morphological (light microscopy) and ultrastructural (SEM) studies. This is the first record of the species from the late Pliocene of India. The outer layer of D. gracillima is entirely different from other invertebrates, and the presence of Ridged Prismatic Structure (RRP) exclusively characterises this particular species. The mineralogical analysis (Raman spectroscopy and EDS) reveals a Mg-Ca skeletal for D. gracillima. Isotopic analysis indicates that there is a narrow range of variation in the delta 18 O values of D. gracillima The delta 13 C of D. gracillima shows significant variation and displays the most 13 C depleted values. Based on isotopic analysis it has been inferred that the deposition of sediments took place in a shallow marine environment and D. gracillima thrived in the proximity of hydrocarbon seepages. The present day distributional pattern of D. gracillima indicates that they are mainly confined in the Indo-Pacific region.