Fertilized zhikong scallop Chlamys ferreri eggs, treated with cytochalasin B (CB 0.5 mg/L) at 14-15 min postfertilization until the second polar body (PB2) was released in controlling groups, were examined following FITC-anti-α-tubulin and propidium iodide (PI) staining for microtubular patterns and DNA, respectively.Fluorescent microscopic observations of treated eggs sampled every 2-3min during meiotic maturation revealed meiotic apparatuses assembling and correlated chromosome segregation.In fertilized eggs of CB treated groups, meiosis Ⅰ proceeded normally and produced two groups of dyads, 19 in each group.Both of the two dyad groups were retained in the eggs and entered meiosis Ⅱ.2, 3 or 4 asters (centrosome with microtubules around it) existing in meiosis Ⅱ rearranging the spindle had several patterns: bipolar [24.0±4.1 μm (long axis) × 18.3±4.1 μm (diameter:metaphase plate)], tripolar (18.6±3.9 μm×9.9±1.3 μm), separated bipolar spindles (18.3±2.8 μm× 11.2±1.8 μm), other patterns with special spindles unfamiliar.Corresponding chromosome segregation including bipolar (18.9%), tripolar (38.9%), double bipolar (16.5%) and unclassified pattern (25.6%) were observed during meiosis Ⅱ in CB treated eggs.It was indicated that chromosome segregation patterns determined by spindle patterns and spindle fashion were critically influenced by the number of centrosomes in M Ⅱ eggs from Zhikong scallop, following inhibition of PB 1 with Cytochalasin B.