Cryptic diversity of the tube-dwelling polychaete Phyllochaetopterus in the Shinkai Seep Field, Mariana Trench

Phyllochaetopterus (Annelida: Chaetopteridae) is a diverse genus of tube-dwelling polychaetes found in a wide range of marine environments from subtidal to abyssal depths, including chemosynthesis-based ecosystems. The Shinkai Seep Field (SSF) is a serpentinite-hosted system in the Mariana Trench, where the deepest-known Phyllochaetopterus polychaetes inhabit the surfaces of brucite/carbonate chimneys. Despite all specimens collected from SSF being morphologically consistent with P polus originally described from a deep-sea hot vent on the Mid-Atlantic Ridge, molecular barcoding using the mitochondrial cytochrome c oxidase subunit I (COI) gene revealed at least three cryptic lineages, none of which corresponded to P pa/us. Phylogenetic reconstruction recovered P polus embedded among the three SSF lineages, confirming their close relationship. These results warrant careful examination of Phyllochaetopterus from other regions using integrative taxonomy in order to understand its true diversity and pinpoint further taxonomically informative morphological characters.

Automated summary

Phyllochaetopterus is a diverse genus of tube-dwelling polychaetes found in various marine environments, with a study revealing at least three cryptic lineages in the serpentinite-hosted Shinkai Seep Field. Molecular barcoding using the mitochondrial COI gene showed a close relationship between the Phyllochaetopterus lineages and confirmed the presence of previously unknown diversity. Further integrative taxonomy is needed to fully understand and characterize the true diversity of Phyllochaetopterus.