On the Fine Structure of Gastrotrichs with Description of Chordodasys antennatus sp.n.1

Chordodasys antennatus sp.n. is described from sublittoral sediments off the US Atlantic Coast. This species has been also studied by transmission electron microscopy. The new species is particularly characterized by extremely enlarged sensory processes which have a segmented appearance. The fine‐structure of the chordoid organ, characteristic of the genus Chordodasys, has been studied in both known species of this genus. According to this investigation the chordoid organ consists of plate‐like muscle cells, surprisingly similar to the notochord of Amphi‐oxus. Particular emphasis has been made in this study to elucidate the fine structure of the body cavity and the system of lateral and central chambers as described by Remane in 1936. The electron micrographs substantiate the fact that gastrotrichs exhibit an acoelomate construction of their body cavity. The systematic position of the new species and the genus Chordodasys is discussed in the light of the new ultrastruc‐tural information.