EPIBIONTS ON DROMIOPSIS RUGOSA (DECAPODA: BRACHYURA) FROM THE LATE MIDDLE DANIAN LIMESTONES AT FAKSE QUARRY, DENMARK: NOVEL PREPARATION TECHNIQUES YIELD AMAZING RESULTS

PREPARATION TECHNIQUES

Selection of technique.-The preparation of the Fakse material employs two different kinds of treatment: a mechanical cleaning process by which the surrounding matrix and any remaining cuticle of the specimen is removed, exposing the mold of the interior of the carapace; and the removal of the mold of the interior leaving a mold of the exterior of the carapace in which a cast can be made, the so-called negative preparation. The first step in preparation is to consider the best choice of method.

Partly exposed molds of the interior, selected for the staining method described below, can be cleaned by mechanical tools such as pneumatic air scribes to remove any remaining obscuring matrix. To expose roughly the mold of the interior of a carapace, the Desoutter Power Pen is recommended, as it quickly removes the thicker portion of surrounding matrix. The Murray Engineering Micro-Jacks and the Air scribe W224 are suited for more precise removal of the matrix within intricate portions of the fossils, such as the rostrum and orbits. Subsequently, the molds of the interior can be cleaned using sandblasting or the waterblasting technique described below.

In other cases where the limestone contains numerous crab remains exposed either by hammer and cold chisel or by using hydraulic pressure, a negative preparation has proven to be the fastest, most convenient, and most informative treatment. This is a destructive process in which a mold of the exterior of the carapace is exposed, a cast of silicone rubber or resin (polyester, epoxy) is prepared, and the limestone is removed by acid digestion (Fig. 1). Silicon rubber is preferred, as small individual specimens on a larger cast easily can be cut out using a scalpel for scanning electron microscopic (SEM) examination without any loss of material.

Waterblasting and examination of molds of the exterior of the carapace for epibionts.-Molds of the exterior of decapod carapaces potentially carry information about the epibionts that attached themselves to the crab during its life, those that may have attached to the animal following death, and the surface ornamentation of the cuticle. Epibionts on the interior of the carapaces are clearly postmortem infestations (Waugh et al., 2004). It is not possible to check every specimen from Fakse for epibionts on both sides of the carapace due to preservational condition. All the investigated, stained specimens represent interiors of the carapaces and are, therefore, postmortem encrustations. Examination of the true mold of the exterior is frequently impaired by the presence of a thin layer of exocuticle or epicuticle so that what appears to be the mold of the exterior is, in fact, an intracuticular surface that is a plane of weakness (Waugh et al., 2004). Removal of this material is essential for proper examination of epibionts.

By using an air scribe, most of the enclosed crab remains can be removed and then the surface can be cleaned by high pressurized water from a watergun, such as the Wagner Model W 400 SE. The gun generates a fine, highly powered jet stream of water, adjustable up to 180 bars, that immediately blows off most of the particles in the imprint without harming the surface details.