Six new species of Grania (Oligochaeta, Enchytraeidae) from the Ross Sea, Antarctica

Abstract

Six new species of marine Enchytraeidae, Grania hirsuticauda sp.n., G. acanthochaeta sp.n., G. carchinii sp.n., G. angustinasus sp.n., G. antarctica sp.n. and G. algida sp.n., are described from benthic material collected in McMurdo Sound during 1959–61 and Terra Nova Bay in 1988. They represent the first records of this family from below the Antarctic circle and, together with tubificids, the first oligochaetes from the Ross Sea. G. hirsuticauda, apparently the most widespread species in McMurdo Sound, is distinguished by having setae abruptly larger in the posterior third of the body and almost nodulate; a T-shaped prostomial bifurcation of the dorsal vessel, short sperm funnels and sperm sac, and thick-walled spermathecae. G. acanthochaeta possesses a unique, thorn-like, setal morphology and diverticulate spermathecal ampullae. G. carchinii, the only new species lacking lateral setae, is also distinguished by a remarkably high development of the chloragogen tissue and the possession of nephridia at 6/7. G. angustinasus, the most abundant species in the sampling area in Terra Nova Bay, and G. antarctica, have the same setal distribution, size and (curved) shape, but show different forms of penial bulbs (more complex in G. angustinasus) and spermathecal structures (the ampullae being larger and the external pores more posterior in G. antarctica). G. algida is distinguished by its L-shaped setae and carrot-shaped, diverticulate, spermathecal ampullae. All the new species lack cuticular penial stylets as well as spermathecal ectal glands. All species but G. carchinii are peculiar in possessing, in front of the brain, a middorsal vesicular body of specific shape and size containing a few refractile inclusions; a sensory (possibly a statocyst-like) function is suggested for this ‘head organ’, which has not been previously reported in the Oligochaeta.