Feeding by Priapulus caudatus (Cephalorhyncha: Priapulidae): observations of the effects of seasonal temperature change and molting

The ecdysozoan Priapulus caudatus belongs to a phylum of exclusively marine worms that reigned among the most abundant benthic metazoans during the Cambrian. Usually found at great depths, this species can occasionally be found among intertidal habitats fed by exceptionally cold sea water and predominated by soft mud, as in the Lower Bay of Fundy. Live priapulids were collected there and the effects of molting and seasonally changing ambient sea water temperature on feeding were observed in the laboratory beginning in February. Feeding increased as ambient sea water temperatures increased from March through April, a relationship significantly correlated (p < 0.001). This association rapidly deteriorated once 11 degrees C was reached in May with no animals feeding above 13 degrees C. Priapulids fed until the first molt day when feeding significantly decreased (p = 0.016). This response was short-lived, and feeding slowly resumed among animals within a week post-molt. Exuvia were not consumed. The onset of molting followed color changes in cuticle appearance and was significantly correlated with increasing temperature (p < 0.001). Molting was rapid, with the exuviae clearly separated from the new cuticle within 24 h at places where the process began. Without substrate to burrow into, animals emerged from shed exuviae between 3 and 29 days, with larger animals taking longer. While the cold deep-sea is the primary habitat of P. caudatus, this species shares some of the effects of temperature and molting on feeding shown by other ecdysozoans. The observations made during this study place a limit on where P. caudatus might be found intertidally.