Texel (NL), 29.06.2007 (C.J.M. Philippart)  Characteristics used for id: - smooth  - juvenile: mostly oval - concentric lines - no radiating ribs - colour: blue and juvenile-transparent  References: HENDRIKS, 2002; HAYWARD et al., 2007 Checked by A. Gittenberger (Naturalis, Leiden, NL