Final answer:
Ribosomes do not localize at the leading front of a migrating eukaryotic cell. Instead, structures like lamellipodia are the ones involved in cell motility and are seen at the leading edge. The correct answer is c).
Step-by-step explanation:
The structure that does not localize at the leading front of a migrating eukaryotic cell is c. ribosomes. The lamellipodium is an actin-driven protrusion at the front of migrating cells and plays a critical role in the movement. Centrosomes may be involved in cell motility but are not frontally localized. Ribosomes, on the other hand, are involved in protein synthesis and are not specific to the leading front of migrating cells.
For the other query, it's known that diploids are organisms with two sets of chromosomes and diploblastic eucoelomates is not a possible term because eucoelomates are triploblastic, which means they have three germ layers, not two (diploblastic).