Morphology, Fill and Size: Arenicolites refers to unbranched U-shaped burrows having a subvertical orientation, with or without lining and passive fill (Rindsberg and Kopaska-Merkel 2005; Bradshaw 2010).
Description.—Straight cylindrical burrows, unbranched and oriented perpendicular to inclined to the bedding plane, commonly seen as paired circular openings at the top of the layers. Lined wall and massive fill contrasting with the host rock. Diameter is 3.4–30 mm. Preserved as negative epirelief and exceptionally as full relief. Cross-section views are rarely observed and depth is difficult to measure. Maximum observed length is 70mm.
Ethology and tracemaker.—Arenicolites is a dwelling trace (domichnion) produced by suspension-feeding worms (Häntzschel, 1975) or by detritus and deposit-feeding worms, particularly polychaetes (e.g., Bromley, 1996). In modern environments, similar burrows are produced in coastal environments by deposit-feeding polychaetes of the families Spionida (e.g., Gingras et al., 1999) and Carpitellida (e.g.,Dashtgard, 2011), as well as by suspension-feeding amphipod crustaceans and deposit-feeding sipunculids (e.g., Baucon and Felletti, 2013).
Diagnosis: Simple U-tubes without spreite, perpendicular to bedding plane; varying in size, tube diameter, distance of limbs
and depth of burrows; limbs rarely somewhat branched, some with funnel-shaped opening; walls commonly smooth, occasionally
lined or sculptured; burrows may reach considerable depth (Häntzschel, 1975).
Simple, U-shaped, vertical burrows without spreiten. Walls are smooth with thin lining. Burrow fill is identical to host rock. Burrow depth is 17.2-40.0mm; arm width is 4.0-11,4mm; spacing between is arms 71.4-201.7mm. Preserved as full relief.