Planolites Nicholson, 1873

Planolites is a eurybathic, facies-crossing ichnogenus, which occurs from the Precambrian to the Recent (Häntzschel, 1975). It is referred to polyphyletic, vermiform deposit feeders producing active backfilling (e.g., Pemberton and Frey, 1982; Fillion and Pickerill, 1990).

Remark. Planolites is interpreted as feeding burrows (fodinichnia) of deposit-feeders (Pemberton and Frey, 1982), and ranges in age from Cambrian to Holocene (Häntzschel, 1975; Mángano and Buatois, 2014). Planolites is found in almost every depositional environment (Pemberton and Frey, 1982)

Diagnosis. Unlined, rarely branched, straight or tortuous, smooth surface, irregular or annulated, circular or elliptical in cross-section, of variable dimensions and configuration; homogeneous, structureless in fillings of burrows, differing in lithology from the host rock (Pemberton and Frey, 1982; Stanley and Pickerill,1998).

Ethology and tracemaker.—Planolites is a feeding structure (fodinichnion) interpreted as produced by deposit-feeding vermiform organisms that actively fill their burrows (Pemberton and Frey, 1982; Fillion and Pickerill, 1990; Uchman, 1995).

Diagnosis: Relatively large, unlined, smooth-walled, horizontal to undulant, straight to sinuous cylindrical burrows; fills typically differ in color from surrounding sediments.

Straight to slightly or markedly undulose and meandrous, rarely branched, cylindrical or subcylindrical or irregularly developed, unlined burrows, walls smooth to transversely or obliquely annulate. Dimensions commonly vary within given specimens. Branching, where present, exibits no particular patten; nor dos overall burrow configuration, other than a tendency toward horizontal expansion. Individual segments may be parallel, inclined, or normal bedding. Small burrows, and larger ones where crowded, tend to be more highly curved or tortuous than uncrowded large burrows; where burrows are dense, crossovers, interpenetrations, and reburrowed segments are common. Burrow fills are structureless, except for comparatively rare, poorly developed bacfills, and consist or sediments lithologically different from the host matrix. Preserved as endichnia, hypichnial ridges and epivhnial grooves.