Oligodendrorhynchus hesperides gen. et sp. n. (Heteronemertea) from the Bellingshausen Sea

A new genus and species of heteronemertean from the Antarctic (Bellingshausen Sea), Oligodendrorhynchus hesperides, is described and illustrated. Some morphological features with major systematic significance are following: the mode of branching of the proboscis and its low number of terminal branches; the lack of horizontal lateral cephalic slits but in their place a pair of shallow epidermal depressions; a gelatinous amorphous connective stratum between the outer longitudinal and circular muscle layers; the presence of a rhynchocoelic nerve; isolated fibres of the rhynchocoel circular muscle layer interwoven with bundles of the adjacent body-wall inner longitudinal muscle fibres in the intestinal region. Other anatomical characters which can also be used to distinguish the new taxon from existing heteronemertean species that have a branched proboscis are also discussed.