Two new closely related deep-sea species of Paramesochridae (Copepoda, Harpacticoida) with extremely differing geographical range sizes

摘要

Two new species of Emertonia (Paramesochridae) were collected during cruises of RV “Meteor” to the Great Meteor Seamount (1998), the Angola Basin (2000) and the Guinea Basin (2005) and of RV “L’Atalante” to the Pacific Nodule Province (2004). The widely distributed Emertonia clausi sp. n. was represented by 13 individuals found in depths from 4,005 m to 5,389 m in Atlantic and Pacific abyssal plains. A revision of material from the plateau and the slope of the Great Meteor Seamount revealed that E. clausi sp. n. is one of the rare eurybathic species of Harpacticoida, as it was also found at the plateau and the slope of the seamount. Emertonia ingridae sp. n. was represented by two individuals reported only from the Atlantic Guinea Basin at 5,139 m and 5,167 m water depth. The new species are placed in Emertonia due to their characteristic swimming legs with 1-segmented endopods in P2–P4 with one apical setal element. E. clausi sp. n. and E. ingridae sp. n. are closely related species, as they have many characters in common, but differ in subtleties. Unique features of both, E. clausi sp. n. and E. ingridae sp. n., are the single seta in enp2 P1 and the structure of seta V of the furcal rami, which changes from robust to flexible after approximately 0.4 × the length of the seta. The robust part of the seta carries in E. ingridae sp. n. two spinule pairs, in E. clausi sp. n. three pairs, the distal pair being situated at the point of structure change. The drawn-out parts of the baseoendopods of the female P5 are cleft medially and angled at the distal ends in both species. The most obvious differences between the two species are the relationship of length to width of the furcal rami, the total length of the furcal rami compared to the three last body somites, the articulatedon-articulated base of seta VII at the furcal rami, and the presence/absence of a seta at the syncoxa of the maxilliped. The new species presented here raise the number of valid members of the genus to 39.