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The exposed calcareous rocky area of the Abu Qir Headland, east of Alexandria, Egypt whichrange from coarse grains, through pebbles, cobbles, and boulders to rocky platforms, was significantlycolonized by sclerobionts (epibionts and endobionts). The epibiont species diversity was comparativelyhigher than that of endobionts. Epibiont communities included bryozoans (the anascan-grade cheilostomeBiflustra savartii), serpulid (Hydroides elegans, Spirobranchus cf. tetraceros, Vermiliopsis striaticepsand Protula or Apomatus) and spirorbid (Spirorbis) wormtubes, and balanoid barnacles (Amphibalanusamphitrite, Balanus trigonus, and Perforatus perforatus). The cheilostome bryozoan colonies, whichdeveloped extensive sheets, proliferated on the study rocky shore either encrusting the bioeroded basementdirectly, or encrusting other epilithic taxa, particularly balanoid barnacles and serpulid worms. Encrustersdisplayed a remarkable marginal competitive interaction (overgrowth and stand-off) for space on the studyrocky shore. On the other hand, endobionts were not well represented on the studied rocky shore exposure.It was possible to identify three ichnotaxa: Gastrochaenolites, Maeandropolydora, and Finichnus. Thefindings documented represent a significant contribution to our knowledge of sclerobionts composition,sequence of their colonization and/or bioerosion, and their mutual relationships on the intertidal rocky shoreof the Abu Qir Headland. Fil: El Hedeny, Magdy. Alexandria University. Faculty Of Science. Department of Geology; Egipto Fil: Rashwan, Mohamed. Alexandria University. Faculty Of Education. Department of Biological and Geological Sciences; Egipto Fil: Richiano, Sebastián Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico de Geología y Paleontología; Argentina Fil: Al Farraj, Saleh. King Saud University. College of Sciences. Department of Zoology; Arabia Saudita Fil: Al Basher, Ghada. King Saud University. College of Sciences. Department of Zoology; Arabia Saudita

International audience; Silicified fossils collected in ploughed fields at Gavrus (Calvados, France), mainly mollusc shells, are Bajocian in age, and come from the Oolithe ferrugineuse de Bayeux Formation. The entire formation is highly condensed and most fossils are reworked. Their silicification allowed treatment with dilute hydrochloric acid. This treatment brought to light numerous encrusting sclerobionts: Porifera (3 taxa), Bryozoa (n), Polychaeta (9), Brachiopoda (n), Bivalvia (5). The borings and bioerosional traces are described using the “categories of architectural design” as defined by Buatois et al. (2017). Among the 28 ichnotaxa described (corresponding to an ichnodisparity of 14), Planavolites wisshaki isp. nov., Kleithrichnus belemnophilus igen. nov., isp. nov. and Foggara foggara igen. nov., isp. nov. are new. Some Gastrochaenolites dijugus Kelly and Bromley, 1984 borings accommodate the shell of the presumed borer Lithophaga fabella J.-A. Eudes-Deslongchamps, 1838. A group of Nododendrina europaea (Fischer, 1875) on a belemnite rostrum provides a good instance of an ichnogenetic series. Encrusting sclerobionts and macroscopic boring and bioerosional trace-makers are dominantly suspension feeders. The ichnofacies is a peculiar Entobia-ichnofacies, found in deeper, lower-energy environments than the “classical” coastal Entobia-ichnofacies, on deep shell-grounds far from the coast, in the deep euphotic zone.; Les fossiles silicifiés recueillis dans les labours à Gavrus (Calvados, France), principalement des coquilles de mollusques, sont d’âge bajocien, Formation de l’Oolithe ferrugineuse de Bayeux. Toute la formation est fortement condensée et la plupart des fossiles sont remaniés. Leur silicification autorise un traitement à l’acide chlorhydrique dilué. Cette décalcification a révélé de nombreux sclérobiontes encroûtants : spongiaires (3 taxons), bryozoaires (n), polychètes (9), brachiopodes (n), bivalves (5). Les perforations et traces de bioérosion sont présentées en suivant les « catégories de style architectural » définies par Buatois et al. (2017). Parmi les 28 ichnotaxons décrits (correspondant à une ichnodisparité de 14), Planavolites wisshaki isp. nov., Kleithrichnus belemnophilus igen. nov., isp. nov. et Foggara foggara igen. nov., isp. nov. sont nouveaux. Dans quelques perforations Gastrochaenolites dijugus Kelly and Bromley, 1984, on retrouve la coquille du perforant présumé Lithophaga fabella J.-A. Eudes-Deslongchamps, 1838. Un groupe de Nododendrina europaea (Fischer, 1875) sur un rostre de bélemnite fournit un bon exemple d’une série ichnogénétique. Les encroûtants, perforants et producteurs de bioérosion macroscopiques sont pour la plupart des suspensivores. L’ichnofaciès est une variété de l’ichnofaciès à Entobia, dans un environnement plus profond et d’énergie plus faible que l’ichnofaciès à Entobia côtier classique, sur un fond coquillier profond, loin de la côte, dans la zone euphotique profonde.

La información sobre cirripedios como componentes fósiles de las comunidades de substratos duros de latitudes medias en el Hemisferio Sur es escasa. Los cambios en estas comunidades durante episodios de extinción como el que ocurrió durante el límite Cretácico/ Paleógeno (K—Pg), son casi desconocidos. En este trabajo describimos los cirripedios incrustantes y perforantes asociados a ostras maastrichtianas y danianas, evaluamos los procesos tafonómicos involucrados, y registramos los cambios en su frecuencia de ocurrencia en el tiempo. Se estudiaron 1.174 valvas pertenecientes a nueve especies de ostras, recolectadas de las formaciones Jagüel y Roca de la Cuenca Neuquina. Se registró la presencia/ ausencia de los cirripedios o de sus trazas bioerosivas, se calcularon las frecuencias de incrustación y bioerosión y se realizaron análisis tafonómicos y estadísticos. Los cirripedios incrustantes identificados fueron asignados a Verruca rocana, y sus trazas asignadas a la icnoespecie Centrichnus concentricus Bromley y Martinell. Los cirripedios perforantes, están representados por trazas asignadas al icnogénero Rogerella. Los análisis tafonómicos indicaron que durante el Maastrichtiano tardío y Daniano temprano, las ostras muestran una condición intermedia a pobre para la abrasión y la fragmentación, mientras que las ostras del Daniano tardío exhibieron una condición bueña-regular o mixta para ambos atributos. Verruca rocana no muestra registros durante el Maastrichtiano tardío pero sí presenta alta frecuencia de incrustación de valvas luego del límite K—Pg. Los cirripedios perforantes presentaron una declinación en la abundancia durante el Daniano temprano y un aumento en el Daniano tardío. Ambos grupos presentaron un aumento en sus frecuencias durante el Daniano tardío. Information about barnacles as fossil components of hard substrate communities from middle latitudes in the Southern Hemisphere is scarce. Changes in these barnacle communities during episodes of extinction, such as that which occurred during the Cretaceous/Paleogene (K-Pg) boundary, are almost unknown. We describe encrusting and boring barnacles associated with Maastrichtian and Danian oysters, evaluate the involved taphonomic processes and report changes in their frequencies over time. A total of 1,174 valves belonging to nine oyster species, collected from the Jagüel and Roca formations of the Neuquén Basin, were analyzed. Presence/absence of barnacles or their bioerosional traces were recorded, frequencies of host incrustation and bioerosion were calculated and taphonomic and statistical analyses were performed. The encrusting barnacles identified on the oyster shells were assigned to Verruca rocana and, their traces, to the ichnospecies Centrichnus concentricus Bromley and Martinell. The boring barnacles are represented by traces assigned to the ichnogenus Rogerella. A preliminary taphonomic analysis indicated that late Maastrichtian and early Danian shells presented a fair-poor condition given by abrasion and fragmentation as taphonomic attributes while late Danian shells exhibited mostly good-fair or mixed condition for both attributes. Verruca rocana was not recorded during the late Maastrichtian but high frequencies of encrusted valves did become apparent after the K-Pg boundary. Boring barnacles represented by the trace Rogerella exhibited a decline in abundance during the early Danian but an increase during the late Danian. Both the encrusting and the boring barnacles associated with oysters presented an increase in their frequencies during the late Danian. Fil: Brezina, Soledad Silvana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina Fil: Romero, María Virginia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina Fil: Casadio, Silvio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; Argentina

Attached epilithic foraminifera constitute an important but overlooked component of the benthic foraminiferal assemblage in the Pleistocene sediment of the central Arctic Ocean. We report 12 types of epilithic foraminifera that have colonised lithic and biogenic grains found in glacial sediments, including representatives of the generaRhizammina, Hemisphaerammina, Ammopemphix, Diffusilina, Subreophax, Placopsilina, Placopsilinella, HormosinelloidesandTholosina,accompanied by mat-like and ribbon-like forms of uncertain taxonomic affinity. The attached agglutinated forms appear to be colonisers, adapted to extremely oligotrophic conditions.

Encrustation by diverse sclerobionts is found on about 4% of upper Famennian cephalopods from the active Kowala Quarry, Holy Cross Mountains, central Poland. These infested cephalopods are represented mostly by clymeniid ammonites, but also include goniatitids and nautiloids. Sclerobionts on cephalopod shells include crinoids (represented by their holdfasts, about 57% of encrusters), moulds of problematic worm tubes (less common, about 28.5%), bryozoans, microconchids, possible cornulitids and organisms of uncertain affinities. All of the sclerobionts likely utilised shells of dead cephalopods as a hard substrate for their settlement. However, most of the infestation appears on internal moulds because the cephalopod aragonite was dissolved during diagenesis. It is possible that some of the sclerobionts encrusted exhumed lithified internal moulds. These isolated cephalopod shells and internal moulds likely served as benthic islands for various encrusters on a Devonian muddy sea-floor.

International audience; The lower Pleistocene Kritika Member of the Rhodes Formation is composed of predominantly siliciclastic deposits that are sometimes intercalated with hardbottoms formed by drowning of former beachrock beds. A wide variety of sclerobionts occur in this environment, very different from the poorest soft‐bottom populations occurring in other levels of the Kritika Member. The most characteristic, abundant and frequently diverse are the encrusting forms: coralline algae, bivalves, serpulid worms, and bryozoans. Numerous other groups of sessile and vagile organisms are associated with these crust‐forming communities. A number of skeletal organisms (sometimes including zooxanthellate coral colonies) formed small carbonate buildups on top of several beachrock beds. Boring organisms also occur. Evidence for a two‐step deepening succession over the previously formed beachrock is provided by palaeontological and sedimentological data. The rapidly cemented sandy‐conglomeratic beds were first colonised by a relatively shallow‐water (around 20 m) biocoenosis of mostly encrusting organisms. Another association, with encrusting and erect organisms, was later established in a deeper environment (20-40 m). A comparison with Holocene beachrock occurring on the coast of Rhodes was also undertaken. Their submerged part provided habitat for poorer but similar biotas to those occurring in the Kritika Member. The lower Pleistocene beachrock and associated organogenic fossil assemblages indicate repeated drowning episodes during deposition of the Kritika Member and provide help in sequence stratigraphic interpretations of these siliciclastic deposits. Notably, they can be used as indicators of relative sea‐level changes.