All Monoplacophorans are marine inhabitants grazing on algae and microorganisms on the hard ocean bottom. They live at depths of 200 to 6,000 meters and they range in size from 2 to 35 millimeters. A phylum is usually defined as group of animals having several features common to all or most of its members. This is also where excretory and reproductive organs discharge as well. A Foot used in locomotion and often for digging into the sand or mud bottom where many live.
Biologists use various methods for estimating how closely species are related to each other.
Divergence within a phylum can occur whenever the population is split into two or more groups with no chance of interbreeding. Divergence is generally brought about by such events as habitat changes or competition for food. On the other hand, behavioral, morphological or reproductive differences in a small segment of a population can gradually lead to reproductive isolation, without much physical segregation. They may develop different mating behaviors or breeding seasons, or they may accumulate enough genetic differences to render egg and sperm incompatible. It is due to an accumulation of these changes and other morphological and genetic differences that we have the seven classes of molluscs today.