Diversity, distribution and ecological dynamics of Chaetognatha: A comprehensive review with emphasis on the Indian Ocean

The phylum Chaetognatha represents a group of bilaterally symmetrical, transparent-bodied, arrow-shaped organisms (also called arrow worms) that are ecologically sensitive. The members of the phylum are well known for their importance in serving as pollution and hydrographical indicators. Despite contributing 25 % of the global mesozooplankton biomass and serving as valuable indicators of climate change, studies on phylum Chaetognatha lags behind many other planktonic groups, particularly in the Indian Ocean. Presently, the Chaetognatha research is mostly focused on the fossilised members due to their significance as the earliest known predators. In contrast, the present study offers a comprehensive review of published works on the distribution, migration behaviour and ecological interactions of the extant members of this carnivorous phylum in the Indian Ocean. Various hydrographical conditions of the Indian Ocean like upwelling, oxygen minimum zone (OMZ), monsoon winds, hydrothermal vents, and their impact on the organisms are addressed. This review is the pioneer attempt to consolidate all the aspects of Chaetognatha ecology in the Indian Ocean.