Macroinvertebrate-hosted sclerobiont assemblage from the Upper Miocene Clypeaster-rich beds of the Djebel Murdjadjo (Oran, northwestern Algeria)

Sclerobiont communities from Messinian Clypeaster-rich beds at Terziza (Djebel Murdjadjo, NW Algeria) are described. Endobionts are exclusively composed of domichnial structures of polychaete annelids (Caulostrepsis isp. Maeandropolydora isp. and Trypanites isp.), clionid sponges (Entobia geometrica, E. retiformis and Entobia isp.), and endolithic bivalves (Gastrochaenolites torpedo and Gastrochaenolites isp.). Among sclerozoans, epibionts are represented by barnacles, bryozoans, juvenile oysters, serpulids, and vermetid gastropods (with attachment scar Santichnus mayorali). Host organisms include Ostrea lamellosa, Clypeaster, and Pecten. The studied assemblage is ascribed to the Trypanites ichnofacies, indicating nearshore, high-energy deposition influenced by storm events, and post-mortem bioerosion. Clypeaster-rich beds mark the initial Mediterranean marine transgression on the southern flank of the Murdjadjo horst, characterised by three distinct phases. The bioerosion pattern parallels that of the Tafna basin, suggesting uniform environmental evolution during the Early Messinian.