Vyskyt epibiontnich ostnokozcu v buchavskem souvrstvi (kambrium, drum) u Biskoupek na Radnicku (Barrandien)

Small epibionts observed on shells of the orthid brachiopod Bohemiella romingeri, on hyolith shells, and on a trilobite fragment are described from the Skryje Member of the Buchava Formation from Central Bohemia. Specimens were exclusively sampled in the Biskoupky locality north of Rokycany (Rokycany District). Epibionts are associated with common trilobite, brachiopod, hyolith, mollusc and echinoderm fauna of the Skryje Member similar to that known in the Skryje area, including the index trilobite Eccaparadoxides pusillus.
Epibions are disc shaped, almost circular, 0.7 to 1.9 mm in diameter, with gently narrower lower side faced toward the host shell. The original mineral substance is not preserved, but calcium carbonate is highly probable; the phosphatic material is excluded. The epibiont theca has circular central depression with pentamerous, asterisk-like structure. This structure is interpreted as central area with oral structures similar to the oral field of a small edrioasteroid. Therefore, the echinoderm affinity is suggested. Peripheral rim lacks differentiation into discrete plates, but this may be related to the small size of theca and mode of preservation in siltstone. The theca is not interpreted as an echinoderm holdfast because of a pentamerous and depressed structure in the central area, general knob-like shape, and a restricted contact surface of the epibiont theca with the host shell. The theca is similar to the theca of small isorophid edrioasteroid Protorophus, which is known from the “middle“ Cambrian of Spain, but fine morphological details of our epibiont are not preserved. The thecae may represent young individuals of the edrioasteroid Stromatocystites pentangularis or yet unknown dwarfed edrioasteroid.
With an exception of one specimen attached to the fragment of cephalic shield of trilobite Eccaparadoxides pusillus, other epibiont thecae are attached exclusively to the external surface of brachiopod and hyolith shells. Two specimens attached to hyolith utilize space between substrate on the shell floor and the ventral side of hyolith conch. This low slit was likely attractive sheltered cryptic space for settlement of an edriosteroid larva.
The epibiont is not formally named, but it represents the oldest epibiont known from the Barrandian area of the Czech Republic and is one of the oldest known hard substrate attachers in the Cambrian.

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