A new shellfish poison, pinnatoxin D, has been isolated from the Okinawan bivalve Pinna rauricata. The planar structure was elucidated by extensive 2D NMR experiments, and the relative stereochemistry was deduced by NOESY data and 331.1_ H coupling constants. Pinnatoxin D is a novel amphoteric carboeyclic compound which is composed of a 6,7-spiro ring, a 5,6-bicyclo ring and a 6,5,6 trispiro ketal involving 15 chiral centers