Sabellid worms use their branchial crowns to collect and sort suspended particles for feeding, and in the majority of cases for tube-building. Two examples from the subfamily Fabriciinae are considered.

  • 1
    In Fabricia sabella the pinnules borne on the three pairs of gill filaments possess three rows of cilia. The two rows of latero-frontal cilia move water through the crown and also trap particles from this current and deposit them on the frontal cilia. These transport the particles to ciliated grooves in the gill filaments, where a little preliminary sorting occurs as they move towards the centre of the crown. The final sorting occurs at the centre of the crown: large particles are rejected whilst the small ones are carried to the mouth. The medium-sized particles are either mixed with mucus and incorporated into the tube or, when the animal is not tube-building, they are rejected.
  • 2
    In Manayunkia aestuarina the four pairs of gill filaments and the pair of tentacles are devoid of pinnules, but bear three rows of cilia. Usually two pairs of gill filaments are moved over the surface of the substratum and particles are collected from it by the latero-frontal cilia. The particles are then deposited on the frontal cilia in the gill-filament groove; this is deposit feeding. Particles disturbed during deposit feeding become suspended in the water and are then trapped by the latero-frontal cilia on the remaining gill filaments and the tentacles; this is secondary suspension feeding. Particles already in suspension are also utilized; this is suspension feeding. Particles collected by these three methods are moved down the gill-filament grooves, where a little preliminary sorting occurs. As in Fabricia, the particles are completely sorted in the centre of the crown. The large particles are rejected, small particles move to the mouth and the medium-sized particles travel to the ventral lip where they are coated with mucus and incorporated into the tube or, as in Fabricia, rejected.
  • 3
    The development of the abfrontal cilia, the sorting mechanism in the gill filaments and the presence of mucous glands in the pinnules and other gill-filament structures of the larger sabellids, are considered in the discussion.