Middle Devonian microconchids and anticalyptraeids (Tentaculita) from the northern shelf of Gondwana (Morocco): palaeoecological and palaeobiogeographical implications

Microconchid and anticalyptraeid tubeworms from the Middle Devonian of Morocco are described for the first time. The assemblage, coming from the locality of Madene el Mrakib (Mader Basin, eastern Anti-Atlas), consists of one microconchid species, Palaeoconchus sanctacrucensis, and one new anticalyptraeid species, Anticalyptraea madenensis. Both species encrusted uppermost Eifelian/lowermost Givetian brachiopod shells. P. sanctacrucensis was hitherto only known from the upper Emsian-upper Eifelian of the Holy Cross Mountains, Poland. Thus, its presence in the shelf habitats of northern Gondwana implies its migration from the southern margin of Laurussia during the transgression associated with the late Eifelian Kacak Episode. The encrustation patterns of the brachiopod shells by the Moroccan microconchids indicate that the brachiopods only served as favourable hard substrate for colonisation by the microconchid larvae. However, the occupation of different valves of the same brachiopod by microconchids and Anticalyptraea may imply that both encrusters potentially avoided direct competition for suspended food particles. Characteristics and position of Oichnus borings present on a few microconchids and anticalyptraeids indicate that they were not necessarily formed syn vivo and produced by predatory organisms. It is likely that they were drilled by some tiny suspension-feeders and may represent non-predatory domichnia.