Life History & Behaviour

P. nigrescens reproduces diociously, and its gameters are released from the minute gonad, and fertilisation occurs in open water (Cutler 1994). Cleavage during development is spiral, unequal, and holoblastic (Ruppert et al., 2004). P. nigrescens follows Rice’s (1975) IVth pattern of development which is characterised by a long-lived planktonic pelagosphera larva. Once the larvae sense an adequate environment in which to develop, they metamorphose into vermiform juveniles,  adopt a benthic existence and gradually metamorphose into adults (Jamieson, 1999; Rice, 1986).

            P. nigrescens feeds via deposit feeding, using its small nuchal tentacles at the apical end of the introvert. The tentacular crown is retracted by introvert retractor muscles, which attach to the posterior end of the trunk, and elongated by circular muscles around the epidermis (Cutler, 1994). Due to the relative simplicity of Sipunculid muscle structures, P. nigrescens has very limited mobility outside of its coral burrow.