Co-Occurrence of Schizasterid Echinoids and the Trace Fossil Scolicia, Pleistocene, Greece; Facts, Myths, and Fascioles

Most families of the endobenthic spatangoid echinoids possess a subanal fasciole surrounding drain-constructing podia and correspondingly construct a single drain tube or a pair of them. The drains conduct used respiration water away from the echinoid. In vitro studies of spatangoid echinoids in the laboratory in aquaria have led to the description of some spurious behavior patterns. These probably derive from the use of inadequately spacious aquaria and of insufficient duration of experiments, and have led to abnormal behavior of the echinoids. Some of these "mythical" behavior patterns have been repeated in the literature, especially in textbooks. Trace fossils of burrowing echinoids are abundantly and well preserved as Scolicia (twin drains) and Bichordites (single drain), and these trace fossils provide evidence that the spurious modes of behavior observed in laboratory conditions are artefacts and do not exist in nature. Some members of the family Schizasteridae burrow deeply down to ca. 20 cm in fine-grained sediment. However, the schizasterids possess no subanal fasciole, and little evidence of drain construction has been reported for the family. Nevertheless, large podia are present, which suggests the ability for construction and maintenance of two drains. In the Pleistocene Lindos Bay Clay of the Rhodos Formation of Rhodes, Greece, abundant individuals of Schizaster canaliferus are preserved in silty clay. The sediment is totally bioturbated, containing abundant Scolicia isp. The echinoids occur in intimate association within these trace fossils and are undoubtedly genetically connected with them. The Scolicia have two basal drain strings, clearly indicating that S. canaliferus constructs a pair of drains. Preservation of the hair-thin drains in Scolicia is considered to involve precipitation of early cement, as in Bichordites. In this way, the slender empty tubes escape obliteration by compaction.