One of the largest noticeable differences between sea stars and sea urchins in early development is the formation of polar bodies. A polar body is a tiny sister-cell of the primary oocyte, produced during meiosis. It contains discarded DNA, and very little of anything else. Polar bodies are not usually observed in sea urchin, because meiosis is completed within the ovary, and spawned eggs have already parted with their polar bodes.
However, we were able observe polar bodies in sea stars. This is because in sea stars, sperm entry occurs before the oocytes have completed meiosis (cell division, reducing the number of chromosomes). Polar bodies form after fertilization and are trapped within the fertilization envelope. The photos here show an immature unfertilized oocyte (with a large nucleus and a nucleolus inside) and a fertilized secondary oocyte with homogenenous cytoplasm, a tight fertilization envelope around it, and one polar body (at about 5 o'clock), in the ochre sea star Pisaster ochraceous. The fertilization envelope in starfish is much closer to the surface of the egg than in sea urchins.