Opercular regulation in the polychaete Hydroides dianthus (verrill, 1873) II Control of opercular regulation

Abstract When the adult functional operculum of the serpulid polychaete Hydroides dianthus is amputated at any level below the secondary cup, the rudimentary operculum develops into a functional one. Concomitantly a new rudimentary operculum regenerates from the stump of the former functional operculum. This reversal of asymmetry is proportional to the degree of injury (e.g., amputation > crushing > ligation > puncture). Amputating the rudimentary operculum does not affect the functional one, but in some cases the regenerating rudimentary operculum may differentiate into a second functional operculum. When distal portions of both opercula are removed, reversal occurs, and if the two opercula are amputated simultaneously at the base, a functional operculum regenerates on the side opposite its original position. If, however, the branchial apparatus is amputated together with both the functional and rudimentary opercula, the latter tends to regenerate on the original side. Thus the opercular regulatory system distinguishes between degrees and types of injury to the functional operculum, and the branchiae may be involved in opercular relationships. If the animal is decerebrated or the supraoesophageal ganglion is bisected, the opercula are still able to reverse normally. No reversal occurs when the external opercular nerves are severed, but in about one‐third of the animals reversal occurred after section of the internal nerve. No direct nervous connection is involved in opercular communications, but the internal opercular nerve is implicated in stimulating reversal.