"This book brings to light for the first time many interesting features in 25 minor phyletic invertebrates without being constrained by phylogenetic considerations. 1. Most of these phyla are not speciose. However, some species abound at densities of million/m2, a few flourish in anoxic habitat and a few others thrive in hot springs at 45-61°C. 2. In them, parthenogenesis and clonal multiplication eliminate each other. 3. Pseudocoelomates are all eutelics, i.e. mitosis ceases after hatching. 4. Increase in tissue types seems to reduce parasitic mode of life from 99.9 % in Aorganomorpha to 42 % in pseudocoelomate Nematoda, 8 % in hemocoelomate Pentastomida and 0 % in eucoelomates. Relation between coelom type and regeneration is elaborated. Indirect life cycle with feeding larval stages increases the scope for speciation"--