Pendant with a nature cast of the shell of a sea snail Tenagodus obtusus that is endemic to the Mediterranean and north-western Atlantic. Typical for the species is the spirally coiled shell with separated whorls and an opening along its longitudinal axis. This shape is the result of the natural lifestyle in a fixed position within a sponge, a sessile salt-water animal that slowly grows in unpredictable directions. To keep its access to the outside of the sponge, the Tenagodus adapts the growth of its shell to that of the host sponge.