Polychaetes' Structures:

The head or acron is represented by the prostomium and contains the brain. It is one of the main distingushing features.

The prostomium projects over the mouth like a shelf. Behind it is the peristomium. The prostomial sense organs consist of :

  • eyes
  • antennae
  • palps

The peristomium bears :

  • sensory tentacular cirri
  • feeding appendages: tentacular palps
  • eversible proboscis

Some families are identified by the presence of their highly modified heads bearing heavy, conspicous setae. In the Sabellariids, two fused segments have grown forward and block the tube entrance.

The pectinariids have a head which bear large, conspicous setae used for digging in soft mud or sand. Sediment particles are collected by during feeding.

The sabellids and serpulids have prostomial palps developed to form funnel-shaped or spiral crown consisting of many pinnate processes called radioles.


The beating of the cilia on the pinnules produce a current of water that flows through the radioles into the funnel and then flow upward and out. Particles are trapped on the pinnules and are driven by the cilia into the groove running the length of each radiole.

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