Kliopsyllus andeep sp. n. (Copepoda: Harpacticoida) from the Antarctic deep sea—a copepod closely related to certain shallow-water species

The international scientific deep-sea cruise ANDEEP-2 (ANT XIX/4) to the Scotia Arc and the northern Weddell Sea in 2002 revealed a new species of the family Paramesochridae (Copepoda: Harpacticoida). Kliopsyllus andeep sp. n. can be distinguished from its congeners by characteristics such as a two-segmented endopod on the fourth leg and an additional seta on the endopod of the third leg. The most striking feature is its strong, flexed, chitinous thorns on the telson. Only three species in the family have such appendages, all of them interstitial, shallow-water species. Because the new species lacks the strong abdominal muscle observed by Kunz in Kliopsyllus furcavaricatus Kunz, 1974, it cannot spread its furcal rami using the thorns on the telson as antagonists the way the shallow-water species does. The furcal-rami spreading system, which is an adaptation to interstitial living, for K. andeep sp. n. is irrelevant, because the species has been collected from muddy sediments. Therefore, the abdominal muscle might have been lost during the species’ evolution.