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The community structure of meiofauna was assessed relative to environmental parameters in four zones (non-mangrove, Avicennia zone, mixed zone, and Rhizophora zone) of Pichavaram Mangrove Forest, which is located along the southeast coast of India. Field sampling was carried out from June 2016–May 2017. The meiofaunal data were evaluated using univariate and multivariate statistics. The highest abundance of meiofauna (434 ind/10 cm−2) was recorded in the Rhizophora zone and the lowest (270 ind/10 cm−2) in the non-mangrove zone. A total of 62 species representing four meiofaunal groups were recorded, including 38 species of foraminifera, 12 species of nematodes, seven species of ostracods, and five species of harpacticoids. Diversity (Shannon H′) mostly ranged from 3–4, and was highest (3.86±0.26) in the Avicennia zone and averaged ∼3.3 in the other three zones. The Margalef richness index was ∼6 in the Avicennia and Rhizophora zones and ∼5 in the non-mangrove and mixed zones. The BIO-ENV and CCA analyses identified sediment texture and organic matter as key variables influencing the distribution of meiofauna, while % calcium carbonate, salinity, and sediment pH were also important. Monitoring studies of meiofaunal taxa may help elucidate their roles in coastal blue-carbon cycling and will also contribute to understanding how mangrove-associated habitats influence meiofaunal distributions.

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Pisione Grube, 1857 was considered rare animals, but its numbers have increased in recent decades. New species have been described, mainly from the Indo-Pacific region. In this study, we described Pisione balasubramaniani sp. nov., from Tamil Nadu, southeastern coast of India. The new species resembles other species in the ‘remota complex’ in the shape of the copulatory organs, elongated ventral cirri on the first segment and a short dorsal cirrus on the second segment. It can be distinguished from members of this group by having protruding notoacicula from the anteriormost to the very last chaetigers, three pairs of copulatory organs on chaetigers 15–17 and variances in the morphology of the copulatory organ. We also provide an updated comparison between all known species of Pisione based on key morphological characters. We also present a discussion of species of this genus in India and nearby regions.