Marine Enchytraeids (Oligochaeta) of the Coastal Northwest Atlantic (Northern and Mid U.S.A.)

Abstract

Nine species of subtidal marine Enchytraeidae of the genera Randidrilus gen.n., Marionina Michaelsen, 1889 and Grania Southern, 1913 are described from the continental shelf off the northeast U.S.A. Randidrilus is briefly defined as: marine enchytraeids lacking lateral (=dorsal) setae, but possessing single ventral setae; dorsal lobes of pharyngeal glands united; penial bulbs with two separate glandular masses, one anterior and one posterior; spermathecae connected to oesophagus, one pair in V or two pairs in V and VI. Two species are included, R. codensis (Lasserre, 1971) comb.n. and R. quadrithecatus sp.n., with, respectively, one and two pairs of spermathecae. Randidrilus is similar to Grania in setal numbers and general appearance but differs in possessing a distinct form of penial bulb, in overall setal distributions and in compactness of the pharyngeal glands. The description of Marionina welchi Lasserre, 1971 is amended slightly to indicate the occasional absence of setae in XI through XIV and the presence of small ‘diverticula’ on the ampullae of the spermathecae. Marionina diazi sp.n. is distinguished from M. welchi and from the other species by possessing single setae in ventral bundles only and very long spermathecae connected to the oesophagus at the posterior of VI. Five species of Grania, G. reducta sp.n, C. levis sp.n., G. atlantica sp.n., G. monospermatheca ErsCus & Lasserre, 1976 and G. longiducta Erséus & Lasserre, 1976, new rank, are described. Details of the structure of the male ducts and associated glands are very informative for the recognition of species. Grania levis, G. longiducta and G. monospermatheca all possess terminal ‘stylets’ on the vasa deferentia, the latter species, in addition, has muscularized vasa deferentia; G. reducra and G. atlantica lack such modifications. Grania levis is the first described species of Grania without setae. Grania atlantica is widely distributed in the Atlantic Ocean at depths from about 740 m to about 1800 m. Records of the other species are limited to the northwest Atlantic at depths less than 100 m.