A new species of Raricirrus (Polychaeta, Ctenodrilidae) from the continental slope of the Laptev Sea near the Gakkel Ridge

Abstract

Raricirrus arcticus sp. nov. is described with specimens collected near the Gakkel Ridge, Laptev Sea, from one station in the hydrothermal area, at nearly 2000 m. The new species differs from the other species of the genus in the presence of long serrate chaetae with thin straight tips in neuropodia of the middle part of the body, and in the position of the heart body, which first appears much more anteriorly than in all previously described species of both genera comprising the subfamily Raphidrilinae Hartmann-Schroder, 1971. Raricirrus arcticus sp. nov. is likely most closely related to the geographically nearest R. beryli Petersen et George, 1991 sharing the absence of a modified region with enlarged spines and the presence of distinct ventral ciliary fields in the area of the mouth and the neural ciliary band on a few anterior segments. Asexual and sexual reproduction is noted for the new species. The hypothesis of Petersen and George (1991) about the role of the heart body in the head regeneration process is supported by revealed correlation of the anteriormost occurrence of the heart body with the number of segments in anterior regenerates in R. arcticus sp. nov., as in other Raricirrus species. Systematic position of the family Ctenodrilidae and taxonomic differences between the genera Raricirrus Hartman, 1961 and Raphidrilus Monticelli, 1910 are discussed. Morphological characters useful in distinguishing species within the genus Raricirrus are defined. A key to identify the known species of Raricirrus is given.