A new species of the sabellid genus Pseudobranchiomma is described from 50 cm depth in dock fouling from the southern Gulf of California. Pseudobranchiomma schizogenica sp. nov., belongs to a group of six species characterized by having radiolar serrations extending for most of the radiolar length. The new species is characterized by the presence of a unique set of features related to the covering of the peristomium by lateral collar margins, the shape of the first ventral shield, the size of interramal eyespots, and the width of the hood of thoracic and abdominal spinelike chaetae. Information about live and post-fixed colour, glandular pattern and reproduction is also provided. The new species described here is compared with all species in the former group. The presence of paired patches of cilia without heads (kinocilia-type) on ventral lappets and ventral shields of the collar, thorax and abdomen is documented for the first time in the genus Pseudobranchiomma. Dense aggregations of Pseudobranchiomma schizogenica sp. nov., on docks from the southern Gulf of California are predominantly a result of asexual reproduction taking place during summer, when 82% of the population reproduces by architomy.