A new species of Diosaccus Boeck, 1873 (Arthropoda, Hexanauplia, Harpacticoida) was recently discovered in Korean waters. The species was previously recognized as D. ezoensis Ito, 1974 in Korea but, here, is described as a new species, D. koreanus sp. nov., based on the following features: 1) second inner seta on exopod of fifth thoracopod apparently longest in female, 2) outer margin of distal endopodal segment of second thoracopod ornamented with long setules in male, 3) caudal seta VII located halfway from base of rami (vs. on anterior extremity in D. ezoensis), and 4) sixth thoracopod with three setae in female (vs. 2 setae in D. ezoensis). In addition, there is also a mitochondrial COI sequence difference of more than 19.93% with D. ezoensis registered in NCBI. A key to Diosaccus species of the world is also provided, and new morphological features and DNA sequences are presented for two other harpacticoid species, Parathalestris verrucosa Ito, 1970 and Peltidium quinquesetosum Song & Yun, 1999. In order to clearly identify harpacticoids at the species level, both morphological and DNA sequence characteristics should be considered.

This study reports the discovery of four new benthic harpacticoids from Korean waters in the Pacific Ocean. The harpacticoids were collected using SCUBA or a grab sampler and sorted using a stereomicroscope for both molecular and morphological analysis. The study employed standard DNA sequencing methods (COI and 18S rRNA) and detailed morphological characterization through microscopy and scanning electron microscopy. As a result, three new species belonging to the family Orthopsyllidae and classified as a new genus were discovered. Although the new genus lacks brush setae on leg 1, a diagnostic feature of Orthopsyllidae, it shares similarities with other orthopsyllids in characters such as the large thorn-like process on the antennule, leg 5, and sexual dimorphism. This finding necessitates an expanded diagnosis of Orthopsyllidae to reflect the characters of the new genus based on the three new species. In addition, a new species belonging to the genus Orthopsyllus was discovered. This study is the first to describe a new species of Orthopsyllus from Korea, where the genus has not been previously reported at the species level. This study provides a key for classifying genera and species within the Orthopsyllidae family.

The Deepwater Horizon (DWH) blowout and oil spill began on April 20, 2010 in the northern Gulf of Mexico (NGOM) deep sea (1525 m). Previous studies documented an impacted area of deep-sea floor totaling 321 km² and were based on taxonomy at the macrofauna family level and the meiofauna major taxonomic level. In the present study, finer taxonomic resolution of the meiofauna community was employed, specifically harpacticoid copepod family biodiversity. Severe or moderate impacts to harpacticoid family biodiversity were observed at 35 of 95 sampling stations, covering an estimated area of 2864 km², 8.9 times greater impacted area than previously reported. Sensitive and tolerant harpacticoid families were observed in the impact zone. The present study greatly expands the understanding of DWH deep-sea impacts in 2010 and demonstrates that the harpacticoid family-level response is the most sensitive indicator (reported to date) of this oil spill pollution event.