Final answer:
The barnacle is the organism typical of the upper intertidal zone on rocky shores due to its ability to cement itself to rocks and withstand the harsh conditions of the environment.
Step-by-step explanation:
An organism typical of the upper intertidal zone on rocky shores is the barnacle. Barnacles adhere to surfaces with a cement-like substance, which allows them to remain attached to rocks despite the changing tides and waves that characterize the intertidal environment. While sea urchins, mussel shells, and starfish are commonly found in the intertidal zone, it is the barnacle that is particularly adapted to the upper reaches of this dynamic ecosystem. Sea anemones may be found in the intertidal zone but are more characteristic of lower zones where they can remain submerged longer. Similarly, sea urchins and clams are also found in this zone but are not as exclusively adapted to the variable conditions of the upper intertidal region as barnacles are.