Preliminary Notice of a New Branchiate Oligochæte

Abstract

THE term “Annélides abranches sétigères,” applied by Cuvier to the group which included the terrestrial and fresh-water Annelids, now known as the Oligochæta, is no longer applicable to that group. Several Oligochæta have been described as possessing gills, which, though for the most part differing in structure from the gills of the Polychæta, must be branchial in function. The most remarkable instance hitherto known is Alma nilotica, lately redescribed by Levinsen (Vidensk. Meddel. naturh. For. Kjöbnhavn, 1889) under the name of Digitibranchus niloticus. The posterior segments of this Annelid possess four to five branchial processes on each side of the dorsal middle line of the body. It cannot yet be regarded as an absolute certainty that this species belongs to the Oligochæta at all; but in any case processes of the body-wall, containing each a capillary loop, and therefore probably branchial in function, have been recently described by Prof. A. G. Bourne (Quart. Journ. Micr. Sci., vol. xxxi.) in a new genus of Naids—Chætobranchus. These processes, though doubtless branchial in function, are rather suggestive of the parapodia of marine Annelids, since they inclose, partially or entirely, the dorsal setæ. I have lately had the opportunity of examining this Annelid, through the kindness of Mr. Sowerby. The “Victoria regia tank” at the Botanical Society's Gardens, which produced the celebrated “Fresh-water Medusa” and other remarkable forms, furnished me with Chætobranchus, and with a new and interesting form of branchiate Oligochæte, which I propose to call Branchiura Sowerbii.