Escape hatches for the clonal offspring of serpulid polychaetes

Serpulid polychaetes in the genera Filograna and Salmacina reproduce asexually by releasing a single bud at a time from their posterior ends into their calcareous tubes. Here I show that buds of Salmacina amphidentata gain access to the exterior of these tubes via escape hatches built into the tubes by the parent worms. Each escape hatch consists of a hole in the tube blocked by a calcareous disc that is supported in place by an organic membrane. After buds detach from their parents, the calcareous discs are dislodged, and buds begin to form their own tubes from the resulting openings. Repeated bouts of asexual reproduction result in the formation of aggregations of branched tubes. A survey of Filograna and Salmacina spp. from the Atlantic, Indian, and Pacific oceans suggests that the formation of escape hatches for clonal offspring is common to many members of these genera.