Morphology of gametes in sea urchins from Peter The Great Bay,Sea of Japan

The fine structure of the gametes in six sea urchin species of the Sea of Japan was studied. The sperm in Strongylocentrotus nudus, S. intermedius, Echinocardium cordatum, Scaphechinus mirabilis, Sc. griseus and Echinarachnius parma are species-specific. The conical head and symmetrically disposed ring-shape mitochondrion are common to regular sea urchin sperm cells. S. nudus is characterized by the bulb-shaped head of the sperm; S. intermedius, by a bullet-shaped one. The sperm spearhead and small amount of post-acrosome material are common to irregular sea urchins; the sperm width: length ratio varies for different species, with the highest for Sc. mirabilis. The sperm of Sc. griseus is characterized by two lipid drops in the middle part of sperm. Asymmetrical mitochondrion disposal is usual for E. parma. Actin filaments are found in the postacrosome material in the sperm of heart-shaped sea urchins. The differences in the fine structure of sperm in cosmopolitan species Ech. cordatum inhabiting the Sea of Japan and coastal areas of the Northeast Atlantic may bear record to the complex existence of species Ech. cordatum. The fine structure of sperm is unique for each of the studied families, Strongylocentrotidae, Scutellidae, and Loveniidae. The eggs of all the species are characterized by vitelline and jelly-like membranes. The vitelline membrane is formed by cytoplasm protrusions; the area between them is filled with fibrillar material. The jelly-like membrane is formed by fibrillar material associated with apical parts of microvilli of the vitelline membrane. The irregular sea urchins Sc. griseus, Sc. mirabilis and E. parma are characterized by chromatophores situated in the jelly-like membrane, with the highest abundance in Sc. mirabilis.