Order Euryalida (Echinodermata, Ophiuroidea), new species and new records from the South China Sea and the Northwest Pacific seamounts

Ophiuroids were collected by the manned submersible 'Shenhaiyongshi' from the deep-sea seamounts in the South China Sea and Northwest Pacific regions at 602-1920 m depth, during 2018 to 2020. A total of nine species was identified, including two new species and seven new records from the South China Sea and one new record from the Northwest Pacific region. Two new species are described as Asteroschema shenhaiyongshii sp. nov. and Asteroschema domogranulatum sp. nov. The seven new records included five species from the genus Asteroschema, and one species each from the genera Asterostegus and Astrodendrum. Comprehensive descriptions of morphological features are provided, including characteristics of the arm skeleton, as well as a phylogenetic analysis based on 16S and COI sequences. Intraspecific genetic distance ranges of Euryalida species from the present study were 0.34% to 1.38%, which was relatively low compared to other orders in the class Ophiuroidea. The present study suggests a high probability that species of the order Euryalida are more widely spread around the Indo-Pacific region than previously expected.