Fertilization In Sea Urchin - Malay Nayak 1. What is sea urchin? · Spiny water animal · Phylum ECHINODERMATA · Roughly spherical sea animal Sea Urchin 2. Why Sea Urchin ? The cell-surface events that take place during fertilization have been studied most extensively in sea urchins, members of the phylum Echinodermata . · Sea urchin gametes are easy to collect, · fertilization occurs outside the animal body. · As a result, researchers can observe fertilization and subsequent development simply by combining eggs and sperm in seawater in the laboratory.