A FIRE WORM WITH A SHELTERED LIFE - STUDIES OF BENTHOSCOLEX-CUBANUS HARTMAN (AMPHINOMIDAE), AN INTERNAL ASSOCIATE OF THE BATHYAL SEA-URCHINARCHEOPNEUSTES-HYSTRIX (A AGASSIZ, 1880)

Archeopneustes hystrix Agassiz collected from bathyal depths near the Bahamas carry the amphinomid polychaete Benthoscolex cubanus Hartman i n the intestine. Infection levels as high as 80-100% were found in som e populations, but multiple infection was uncommon. Populations from t hroughout the Bahamas area were found to be infested. Species (n = 23) of bathyal urchin have been examined for presence of the worm, but B. cubanus was only found in A. hystrix. The polychaete feeds by selecti ng foraminiferans and other fragments of organic material from among t he gut contents of the sea-urchin. Although it is able to leave the ur chin, via the anus, the worm is not thought to leave the gut. Benthosc olex cubanus has few obvious adapations for life inside the gut of a s ea-urchin, although the cuticle is thicker than in most polychaetes. S exually mature worms were found at all seasons of the year and maturit y was directly related to size. The sex ratio was 1 : 1 and the size r anges of mature males and females did not differ. Benthoscolex cubanus has small non-buoyant eggs likely to give rise to free-living larvae. Predation is proposed as an ultimate reason for the evolution of this unusual commensal/parasitic relationship.