Abstract: The Xisha Islands constitute an important coral reef region in the South China Sea, but systematic taxonomic studies of octocorals in this area, especially species of the family Ellisellidae, remain relatively limited. During 2024—2025, specimens of Ellisellidae were collected by self-contained underwater breathing apparatus (SCUBA) diving from the waters of the Xisha Islands, and their species diversity was investigated based on morphological observations and phylogenetic analysis of the mitochondrial MutS homolog (mtMutS) gene. A total of 20 specimens of Ellisellidae were collected and identified as four genera and seven species, among which Ellisella ceratophyta (Linnaeus, 1758), Ellisella dollfusi (Stiasny, 1938), Ellisella nuctenea Grasshoff, 1999, and Heliania spinescens Gray, 1859 are newly recorded from Chinese waters. Detailed morphological descriptions are provided for these four species, and, together with historical records, five genera and eight species of Ellisellidae are currently known from the waters of the Xisha Islands. This study improves the species records and morphological taxonomic data of Ellisellidae in Chinese waters, indicating that the Xisha Islands represent one of the areas with relatively concentrated species diversity of Ellisellidae in the South China Sea. The mitochondrial mtMutS gene can provide auxiliary evidence for the identification of some specimens, but the generic boundaries of some groups within this family still require further study based on additional samples and molecular markers.

Key words: Octocorallia, Ellisellidae, newly recorded species, Xisha Islands, mtMutS