The pelagic larvae and youngs of Brachidontes senhausi were traced. The full grown veligers were reared up to the young stage in which the shape, coloration and other characteristics of shell attain to those of shell of young B. senhausi which were found on the natural sea bed. The prodissoconch of the full grown veliger is deeper behind than in front. There are concentric lines on its surface, and many minute teeth present along the hinge line before and behind the umbo. The colour of the prodissoconch is light yellow, and its umbo is purple. When the full grown veliger attains a length between 0.23-0.29mm., mostly 0.23-0.24mm., the velum disappears and it enters into the completely benthic life. In the case of B. senhausi, the prodissoconch is indistinct from the new-dissoconch which is formed after the veliger has entered into the benthic life. The growth of the early young shell continues uninterruptedly through the cold winter season. The direction of major growth of the shell is not so inclined ventro-posteriorly as in Mytilus crassitesta, but somewhat to the anterior, resulting in the formation of a blunt forward projection of the dorsoanterior portion in the shell. The ligament gradually extends to the posterior during growth, and consequently the anterior teeth on the dorso-posterior rim become covered and indistinct. In the adult the surface of the shell is divided into three parts by two zones of radiating striae. This characteristic structure agrees with the genera Botulina and Musculus. The coloration and the pattern of the shell are variable in different individuals.