Structure and function of large, lobed Zoophycos, Pliocene of Rhodes, Greece

In the Kolymbia limestone facies (upper Pliocene) of the Rhodes Formation of Rhodes, Greece, a study was made of a large, spiral form of Zoophycos, named herein Zoophycos rhodensis. In the small bay south of Cape Vagia, two individuals were excavated and dissected while several more were serially sectioned in a vertical plane. The upper parts of the Zoophycos were missing through modern beach erosion, but in one individual the two lowest whorls were almost completely exposed. These comprised a skirt-like zone of spreite surrounded by a zone of 63 marginal lobes. The diameter of the trace fossils was about 1m. Vertical sections demonstrated that the spreiten were composed of material advected downward from a higher horizon, indicating that the spreite was produced nearly 1m below the sea floor. The skirt-like zone of the spreite was constructed of sigmoidal minor lamellae in bundles separated by major lamellae. The radiating major lamellae are not replaced by ridges such as is the case in many other lobed, spiral Zoophycos. The marginal tube and, to a lesser extent, the spreite are mineralised with an oxidised iron mineral, probably once pyrite. The marginal tube is completely filled with sediment and shows no signs of collapse or compaction. This is taken to indicate active backfilling, and that the operative burrow was thus J-shaped and not U-shaped The two zones of the spreite are considered to represent two different modes of behaviour. The skirt-like zone probably represents deposit feeding. The mineralised marginal tube and lobes possibly represent sulphide wells connected with chemosymbiosis between the trace-making animal and sulphide-oxidising bacteria.