A HYOLITH WITH PRESERVED SOFT PARTS FROM THE ORDOVICIAN FEZOUATA KONSERVAT-LAGERSTäTTE OF MOROCCO

Hyolithids are an extinct group of early lophotrochozoans with an external skeleton consisting of four elements: a conical conch, an externally fitting operculum, and a pair of long, flattened spines. Although hyoliths occur in Konservat-Lagerstätten their soft-part preservation has so far been restricted to the gut. A few, differently preserved, examples suggested that a simple U-shaped gut was characteristic of the group and this, together with other lines of evidence, indicated that hyolithids were filter feeders. However, new occurrences showing a diversity of gut configurations among hyolithids revealed some ecological diversity within the group. Here we report an exceptional hyolithid specimen from the Ordovician Fezouata Konservat-Lagerstätte of Morocco which preserves a complete gut, including the mouth and related structures, and soft parts associated with the operculum and the helens. A circular mouth, surrounded by what appear to be radially arranged fine tentacles, opened at the ventral margin of the aperture. The gut is relatively large and complex with at least one small proximal chamber and two continuous tubular segments with markedly different diameters. The anus likely opened dorsolaterally. Extendable soft parts seem to be restricted to the dorsal tissues associated with the operculum. The newly available information suggests that hyolithids were not specialized filter feeders, but had a relatively generalized feeding apparatus consisting of a mouth surrounded by tentacles, which could adapt to various feeding modes in the suspension-detritus-deposit feeding spectrum. Such a feeding strategy occurs in other lophotrochozoan groups, such as polychaetes and sipunculans, the feeding mode depending on modifications of the tentacles surrounding the mouth. The particular gut adaptations of the Fezouata specimen suggest a diet in the suspension-detritus feeding part of the spectrum.