The Cambrian period, (543–503 million years ago) was a time when life exploded onto the planet with diverse phyla, many of which are now extinct. Mollusks, one of the most successful and robust of the phyla, originated in the warm shallow seas of the early Cambrian, and subsequently blossomed into a surprising array of creatures which now haunt the marine and terrestrial environments. Since the Cambrian period, there have been radiations into the shelled bivalve mollusks such as barnacles, clams, oysters, mussels and scallops, as well as other seemingly unrelated creatures such as nudibranchs, chitons, octopus, squid and cuttlefish. Early during this divergence in the late Cambrian period, a shelled mollusk, long since extinct, diverged into cephalopods and gastropods. Although the visual systems of both classes are related, it is the gastropods that have developed a most interesting twist.

The adult Strombus galeatus, pictured on the cover and a member of the family Strombidae, is a robust and hearty vegetarian browsing its way through the sea grass of the Costa Rican continental shelf of the eastern Pacific. These heavily armoured marine gastropods have …