Question

After reading about the five evolutionary trends in invertebrate development, what class of invertebrates belonging to the phylum Mollusca contain species that seem to be an evolutionary anomaly in the steps from primitive to modern nervous systems?

Answer 1

Molluscs are amazingly diverse, with 110,000 named species, second only to the arthropods among all phyla of animals. Molluscs include such familiar creatures as clams, oysters, snails, and octopi. A cephalopod is any member of the molluscan class Cephalopoda such as a squid, octopus, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot. The cephalopod nervous system is the most complex of any invertebrate nervous system. Although species-specific differences exist, its high level of complexity almost certainly is due to the cephalopods’ very active, fast-moving, predatory life style, and their complex behavior and extreme flexibility of response to different environmental situations.The complexity of the cephalopod nervous system and outlines the changes that occurred during the course of evolution, as compared to the basic molluscan design.

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