Complex sentence: Thus, crabs are not all treated in the same chapter; crabs of the rocky shore, high in the intertidal, are in a separate section from crabs of lower intertidal zones or sandy beaches.
Split into simpler sentences: Thus, crabs are not all treated in the same chapter. Crabs of the rocky shore, high in the intertidal, are in a separate section from crabs of lower intertidal zones or sandy beaches.