Taenidium comprises unlined meniscate burrows. Taxonomy of meniscate trace fossils is based on their wall details and the presence or absence of branching (D’Alessandro and Bromley, 1987). Taenidium is distinguished from other meniscate ichnogenus, such as Beaconites Vialov, 1962, Scoyenia White, 1929, and Anchorichnus Heinberg, 1974 by the absence of wall, wall striations, and peripheral mantle, respectively (Keighley and Pickerill, 1994). Taenidium is straight, curved or sinuous, variably oriented, unlined, essentially cylindrical and with meniscate backfilled; secondary successive branching may occur, but true branching is absent (Keighley and Pickerill, 1994). The structure of the meniscate fill is used for Taenidium at ichnospecies level (D’Alessandro and Bromley, 1987; D’Alessandro et al., 1987; Keighley and Pickerill, 1994; Bromley, 1996).
Emended diagnosis. Variably oriented, unwalled, straight, winding, curved, or sinuous, essentially cylindrical, meniscate backfilled trace fossils. Secondary successive branching may occur, but true branching is absent.