Skolithos Haldeman, 1840

Diagnosis. Single, vertical, unbranched burrows, cylindrical or subcylindrical, lined or unlined. Burrows perfectly straight to curved, sometimes inclined to the vertical. Diameter 1–15 mm; length from a few centimeters up to 1m; diameter may vary slightly along lenght of burrow (from Alpert, 1974).

Remarks. Ethologically, this is a dwelling or feeding trace. In the cases where it is found in marine environments, the possible producers are polychaetes or phoronids (Alpert, 1974; also see Sequeira Fernandes et al., 2002 and references therein). Skolithos appears in a variety of shallow marine environments; it has been documented from normal marine settings to lagoons, bays, mouth-bars and fluvial channels
(Uchman et al., 2004).

DIAGNOSIS. Unbranched, vertical to steeply inclined, straight to slightly curved, cylindrical to subcylindrical, lined or unlined structures with or without funnel-shaped top. Wall distinct or indistinct, smooth to rough, some specimens annulated; fill massive; burrow diameter in some individualsslightly inconstant (Schlirf 2000).