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Articulated holaspid specimens of Placoparia Hawle and Corda, 1847 and Eoharpes Raymond, 1905 entombed inside cephalopod conchs and under the remains of large illaenid, asaphid, cyclopygid and dalmanitid trilobites from the Middle Ordovician Šárka Formation of the Prague Basin (Czech Republic) are described and discussed. Two such samples were also found in the overlying Dobrotivá Formation of Middle/Late Ordovician age. Four articulated juvenile exoskeletons of Placoparia preserved under a cephalon of the cyclopygid trilobite Degamella Marek, 1961 represent the first record of shelter strategy of non-holaspid trilobites. The sheltered preservation of trilobites could be explained by a hiding behaviour associated with the danger of predation, storm disturbances, seeking for food or high vulnerability after moulting. It is obvious that Placoparia and Eoharpes deliberately entered the restricted space under skeletal parts of large trilobites or inside cephalopod conchs. These exceptional finds provide a new insight in the life strategy of some Ordovician benthic trilobites and are classified as cases of “frozen” behaviour.

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International audience; The Upper Ordovician (Sandbian) Letná Formation of Bohemia (Czech Republic) provides an important insight into the Early Palaeozoic diversification of marine ecosystems. In this formation, several levels can be interpreted as Konservat-Lagerstätten: they yielded abundant fossil remains, including exceptionally preserved, non-mineralized and poorly mineralized organisms. Non-trilobite arthropods (e.g. Duslia, Furca, Zonozoe) occur together with well-preserved trilobites, echinoderms, brachiopods and bivalves. Recently, a new locality at Chrustenice was discovered in the Letná Formation. It is characterized by mass occurrences of articulated echinoderms, which can be interpreted as storm-induced levels of accumulations (Konzentrat-Lagerstätten) of living or freshly killed individuals. The Chrustenice echinoderm assemblages are particularly diverse and dominated by solutans, associated with various asterozoans, blastozoans, crinoids, edrioasteroids, and stylophorans. The forthcoming description of these new assemblages will bring a wealth of new data on their systematics, functional morphology, taphonomy, palaeoecology, palaeobiogeography, and evolutionary implications. Preliminary investigations of the Chrustenice faunas show the occurrence of several ontogenetic stages in ophiuroids, as well as examples of ecological interaction, e.g. between solutans and edrioasteroids.

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Alfaites romeo gen. et sp. nov. urn:lsid:zoobank.org:act: 2EA9355A-4894-4F7B-AFDA-1000BCE24C3C Fig. 2 Etymology The specific epithet ‘ romeo ’ refers to the Shakespeare’s protagonist Romeo Montague. Marek initially planned to describe two closely related taxa as A. romeo and A. julia. The only specimen designated as A. julia (Fig. 2D) in the original collection of L. Marek does not show any difference in morphology and should be classified as A. romeo. Material examined Holotype CZECH REPUBLIC – Skryje-Týřovice Basin • Inner side of operculum; NM L46640. Paratypes CZECH REPUBLIC – Skryje-Týřovice Basin • Inner side of operculum; NM L 46642 • External sides of operculum; NM L 46646, NM L46641 • Inner mould of conch; NM L 46645 • External moulds of conchs; NM L 46643, L46644. Referred material In addition to the holotype and paratypes, parts of another three conchs and five opercula (collection NM Ls 858), all deposited in collections of the National Museum (Prague, Czech Republic). Type horizon Paradoxides (Eccaparadoxides) pusillus Zone, Skryje Member, Buchava Formation, Drumian, middle Cambrian, Barrandian area, Czech Republic. Diagnosis As for the genus. Description Monoclaviculate operculum with clavicles of bow-shaped transverse cross-section. The angle of divergence of clavicles reaches 135° on the type specimen (NM L46640). Open margins of clavicles overlap above the inner surface operculum (interclavicular concavity). Distal ends of clavicles cut off. Cardinal processes broadly divergent with rounded distal ends, mutually separated by a narrow and shallow groove in linear axis of operculum. Bases of cardinal processes diverging at an angle of 90° toward the dorsal margin of operculum. Uncommon and relatively robust cardinal teeth are developed along the dorsal margin. Cardinal shield is concave in centre and slightly vaulted at the sides. Rooflets clearly distinct and bordered by grooves. Sculpture of operculum consists of growth-lines and fine radial ribs, more distinct near anterior margin of conical shield. Area of operculum adjacent to summit of operculum is nearly smooth. Width and length of inner side operculum is 8.8 mm and 5.5 mm for holotype NM L44640, 7.7 mm and 4.7 mm for paratype NM L44642; width and length of outer side of operculum is 7.6 mm and 4.9 mm for paratype NM L44641 and 6.7 mm and 4.7 mm for paratype NM L44646. Length of the conical shield is 4.0 mm for paratype NM L44641 and 3.7 mm for paratype NM L44646. Conch with subtriangular cross-section. Ventral side very slightly vaulted to almost flat; lateral edges sharply rounded; dorsal side strongly rounded. Amblygonal aperture with dorsal margins vaulted slightly forwardly. The w/h index of conch at aperture is 2.2 (width of aperture of specimen NM L46645 is 7.1 mm and height is 3.2 mm). No apical septa were found. Sculpture consists of transverse rarely anastomosing ribs, which are asymmetrical in transverse cross-section. Ventral side bears only indistinct growth-lines. Conch attained minimum length 30 mm. Occurrence This rare species has been found only at the Biskoupky, Buchava and Hradiště localities. Remarks In his manuscript, Marek (1983) stated that the material collected from the above localities contained another species closely related to Alfaites romeo sp. nov., but presenting opercula with distinctly more vaulted conical shields, higher cardinal shields and a more rounded outline. He even marked the box of one specimen (NM L46646, Fig. 2D) as “ Alfaites julia ” sp. nov., but no significant differences could be observed upon study of the available material.

Alfaites gen. nov. urn:lsid:zoobank.org:act: 6CCEF3A7-D24B-4777-9E08-BFB8DCF68F87 Type species Alfaites romeo sp. nov. Etymology The name ‘ Alfaites ’ refers to the first letter of Greek alphabet – alpha. The cross-section of the conch (Fig. 2H) resembles the large letter alpha and the small letter alpha (turned 90° clockwise) can also be discerned in Fig. 2C. Diagnosis Conch with almost flat slopes of dorsal side; dorsal side broadly rounded; ventral side very slightly vaulted to almost flat; lateral edges sharply rounded. Subtriangular cross-section. Amblygonal aperture. Sculpture of conch consists of transverse rarely anastomosing ribs. No apical septa were found. Monoclaviculate operculum with clavicles of bow-shaped transverse cross-section. Open margins of clavicles overlap above inner surface operculum (interclavicular concavity). Distal ends of clavicles cut off. Bases of cardinal processes diverge at 90° angle. Uncommon and relatively robust cardinal teeth developed along the dorsal margin. Rooflets distinct. Sculpture of operculum consisting of growth-lines and fine radial ribs. Occurrence Buchava Formation, middle Cambrian, Drumian, Skryje-Týřovice Basin, Barrandian area, Czech Republic. Remarks Morphology of both conch and operculum does not allow the classification of Alfaites gen. nov. to any known family of the order Hyolithida. This genus resembles Carinolithes Sysoev, 1958 as emended by Berg-Madsen & Malinky (1999) in the morphology of the cardinal processes, but the operculum of Alfaites gen. nov. is monoclaviculate, thus differing from the platyclaviculate operculum of Carinolithes. Similarly, the shape of the transverse cross-section of the conch (subtriangular in Alfaites and rounded -triangular with distinct keel on dorsum in Carinolithes) and the sculpture (distinct transverse ribs in Alfaites and usually fine growth-lines in Carinolithes) are different. The genus Alfaites, including its type species A. romeo sp. nov., was first recognized as a separate taxon in an unpublished report by the late Ladislav Marek (1983: 36–38).