Involved in the degradation of 3,6-anhydro-L-galactose, which is the major monomeric sugar of red macroalgae. Catalyzes the sixth step of the pathway, the cleavage of 2-dehydro-3-deoxy-6-phospho-D-gluconate (KDPG) to glyceraldehyde 3-phosphate and pyruvate. 2-dehydro-3-deoxy-6-phospho-D-gluconate = D-glyceraldehyde 3-phosphate + pyruvate Belongs to the KHG/KDPG aldolase family.