Confidence: It might be this.
Notes: If it is this species it is only a juvenile of a species which can grow to 5cm long. Both names sourced from the following MarLIN page:
Also included there it says that- "Venerupis saxatilis has a more sculptured shell than Venerupis senegalensis and is typically found attached to firm substrata in rocky crevices. It is unclear whether Venerupis saxatilis is a separate species or an ecophenotype of Venerupis senegalensis (Hayward et al., 1996)."