New species and suborder records reveal unusually high thaliacean (Chordata, Tunicata) diversity in the South China Sea

Abstract

In the context of global biodiversity decline, the monitoring and assessment of marine biodiversity have gained increasing importance. Thaliacea, a group of filter-feeding gelatinous zooplankton, play crucial roles in the carbon cycle and pelagic food webs, yet their diversity remains poorly documented due to challenges in sampling and identification. This knowledge gap is particularly evident in the South China Sea, a highly dynamic subtropical marginal sea. To achieve a comprehensive assessment of thaliacean diversity in the South China Sea, we conducted two cruises in the western South China Sea during the summers of 2020 and 2022. A total of 28 thaliacean species were recorded, representing the highest species richness ever reported from a single study in the South China Sea. Among these, five species are newly recorded, all belonging to the family Doliolidae (order Doliolida): Dolioletta mirabilis Korotneff, 1891, Dolioletta tritonis Herdman, 1888, Doliolina (Doliolina) krohni Herdman, 1888, Doliolina (Doliolina) sigmoides Garstang, 1933, and Doliolina (Doliolinetta) indica Neumann, 1906. In addition, taxa of the suborder Doliopsidina are reported in the South China Sea for the first time. This study expands current knowledge of Thaliacea diversity and distribution in the South China Sea, highlighting the need to reassess their diversity and distribution using integrated methodologies.