Barcoding, structural, and genetic variation of morphologically adopted polychaetes (Annelida: Paronidae, Lumberineridae, Spionidae) using mitochondrial COI gene sequences from the Bay of Bengal shelf including Oxygen Minimum Zone

The structural and genetic variation of morphologically adapted polychaetes from the Bay of Bengal continental shelf (North Indian Ocean) including Oxygen Minimum Zone (OMZ) are described. The density and biomass of polychaetes such as Aricidea curviseta (Paronidae), Lumberineris aberrans (Lumberineridae), Prionospio malmgreni, Paraprionospio pinnata, and Prinospio sexoculata (Spionidae) were significantly differed (P<0.05) in depths (Non-Oxygen Minimum Zone - NOMZ and OMZ), transects and cruises. The response and morphometric measures of branchiae structures were inconsistent between OMZ and NOMZ depths. The species Aricidea curviseta (OR450003 - OR450005), Paraprionospio pinnata (OR436939, OR436941, OR436952 and OR436953), and Prionospio malmgreni (OR436956, OR436957, OR436945, OR436946, OR436947) were barcoded for the first time. The Maximum likelihood tree analysis indicated low ranges of similarity indices among the NOMZ (0.255–0.446 %) and OMZ (0.257–0.443) depths. The total number of mutations and polymorphic sites were 395 and 268, with low haplotypes (12) and nucleotide diversity (among depths: 0.228–0.246, and regions: 0.826–0.100). The groups of haplotypes were also independent of the geographical locations. The AMOVA revealed that the variation among populations was low (regions: −5 %, and depths: −1.86 %) and within populations were high (regions:105.45 % and depths: 101.86 %, respectively). The nMDS indicated that the oxygen factor significantly separated the distribution of density and biomass of polychaetes within transects (density: biomass: F=3.57) and cruises (biomass: F=2.41, P<0.05). Generally, 70–80 % of the total variation was described in four pCCAs by salinity (PSU), pressure, Co, Cu, Fe, Mn, Ni, Pb, Zn, Hg (ppm), and clay (%) with NOMZ and OMZ depths, different cruises, transects and or the interaction between this three. OMZs might not influence the genetic variations. Several additional studies, such as physiological, metabolic, enzymatic, and biochemical, are also be essential for understanding the ecology and evolution of organisms in this habitat.