Marine Biology (2+1)

Polychaetes

The polychaetes of many species including Polydora and Potamilla, bore into limestone rocks and into molluscan shells. The spionid, Polydora makes U-shaped burrows on limestone rocks or moll- scan shells. The boring seems to be effected by the scratching action of the parapodial chaetae aided by acid secretions. Rock boring sea-urchins are common in the littoral waters in many part of the world. Paracentrotus lividus makes round cavities on rock surfaces by the mechanical action of their teeth and spines. They excavate deep pits in the surf-swept shores and shallow depressions in calm waters.