Sea Urchins: Somewhat flattened, globular echinoderms, having thin, brittle shells of calcareous plates. They are useful models for studying FERTILIZATION and EMBRYO DEVELOPMENT.Strongylocentrotus purpuratus: A species of SEA URCHINS in the family Strongylocentrotidae found on the Pacific coastline from Alaska to Mexico. This species serves as a major research model for molecular developmental biology and other fields.Ovum: A mature haploid female germ cell extruded from the OVARY at OVULATION.Lytechinus: A genus of SEA URCHINS in the family Toxopneustidae possessing trigeminate ambulacral plating.Embryo, Nonmammalian: The developmental entity of a fertilized egg (ZYGOTE) in animal species other than MAMMALS. For chickens, use CHICK EMBRYO.Fertilization: The fusion of a spermatozoon (SPERMATOZOA) with an OVUM thus resulting in the formation of a ZYGOTE.Oceans and Seas: A great expanse of continuous bodies of salt water which together cover more than 70 percent of the earth's surface. Seas may be partially or entirely enclosed by land, and are smaller than the five oceans (Atlantic, Pacific, Indian, Arctic, and Antarctic).Paracentrotus: A genus of SEA URCHINS in the family Echinidae found primarily on the western coasts of Ireland.Echinodermata: A phylum of the most familiar marine invertebrates. Its class Stelleroidea contains two subclasses, the Asteroidea (the STARFISH or sea stars) and the Ophiuroidea (the brittle stars, also called basket stars and serpent stars). There are 1500 described species of STARFISH found throughout the world. The second class, Echinoidea, contains about 950 species of SEA URCHINS, heart urchins, and sand dollars. A third class, Holothuroidea, comprises about 900 echinoderms known as SEA CUCUMBERS. Echinoderms are used extensively in biological research. (From Barnes, Invertebrate Zoology, 5th ed, pp773-826)Sperm Tail: The posterior filiform portion of the spermatozoon (SPERMATOZOA) that provides sperm motility.Spermatozoa: Mature male germ cells derived from SPERMATIDS. As spermatids move toward the lumen of the SEMINIFEROUS TUBULES, they undergo extensive structural changes including the loss of cytoplasm, condensation of CHROMATIN into the SPERM HEAD, formation of the ACROSOME cap, the SPERM MIDPIECE and the SPERM TAIL that provides motility.Hemicentrotus: A genus of SEA URCHINS in the family Strongylocentrotidae with a hemicyclic apical disk and short spines.Mediterranean SeaSea Anemones: The order Actiniaria, in the class ANTHOZOA, comprised of large, solitary polyps. All species are carnivorous.Strongylocentrotus: A genus of SEA URCHINS in the family Strongylocentrotidae. They possess more than three pore pairs per ambulacral plate. The species STRONGYLOCENTROTUS PURPURATUS is commonly used for research.Gastrula: The developmental stage that follows BLASTULA or BLASTOCYST. It is characterized by the morphogenetic cell movements including invagination, ingression, and involution. Gastrulation begins with the formation of the PRIMITIVE STREAK, and ends with the formation of three GERM LAYERS, the body plan of the mature organism.North SeaSea Cucumbers: A class of Echinodermata characterized by long, slender bodies.Molecular Sequence Data: Descriptions of specific amino acid, carbohydrate, or nucleotide sequences which have appeared in the published literature and/or are deposited in and maintained by databanks such as GENBANK, European Molecular Biology Laboratory (EMBL), National Biomedical Research Foundation (NBRF), or other sequence repositories.Starfish: Echinoderms having bodies of usually five radially disposed arms coalescing at the center.Ectoderm: The outer of the three germ layers of an embryo.Zygote: The fertilized OVUM resulting from the fusion of a male and a female gamete.Sperm-Ovum Interactions: Interactive processes between the oocyte (OVUM) and the sperm (SPERMATOZOA) including sperm adhesion, ACROSOME REACTION, sperm penetration of the ZONA PELLUCIDA, and events leading to FERTILIZATION.Gene Expression Regulation, Developmental: Any of the processes by which nuclear, cytoplasmic, or intercellular factors influence the differential control of gene action during the developmental stages of an organism.Arbacia: A genus of SEA URCHINS in the family Arbaciidae. They have only one spheridium (stalked body) per ambulacral area (contains tube feet); most sea urchins have several spheridia per area.Hyalin: A clear, homogenous, structureless, eosinophilic substance occurring in pathological degeneration of tissues.Amino Acid Sequence: The order of amino acids as they occur in a polypeptide chain. This is referred to as the primary structure of proteins. It is of fundamental importance in determining PROTEIN CONFORMATION.Egg Proteins: Proteins which are found in eggs (OVA) from any species.Seawater: The salinated water of OCEANS AND SEAS that provides habitat for marine organisms.Base Sequence: The sequence of PURINES and PYRIMIDINES in nucleic acids and polynucleotides. It is also called nucleotide sequence.Blastula: An early non-mammalian embryo that follows the MORULA stage. A blastula resembles a hollow ball with the layer of cells surrounding a fluid-filled cavity (blastocele). The layer of cells is called BLASTODERM.Dyneins: A family of multisubunit cytoskeletal motor proteins that use the energy of ATP hydrolysis to power a variety of cellular functions. Dyneins fall into two major classes based upon structural and functional criteria.Mesoderm: The middle germ layer of an embryo derived from three paired mesenchymal aggregates along the neural tube.Phylogeny: The relationships of groups of organisms as reflected by their genetic makeup.Blastomeres: Undifferentiated cells resulting from cleavage of a fertilized egg (ZYGOTE). Inside the intact ZONA PELLUCIDA, each cleavage yields two blastomeres of about half size of the parent cell. Up to the 8-cell stage, all of the blastomeres are totipotent. The 16-cell MORULA contains outer cells and inner cells.Endoderm: The inner of the three germ layers of an embryo.Larva: Wormlike or grublike stage, following the egg in the life cycle of insects, worms, and other metamorphosing animals.Cyclic ADP-Ribose: A pyridine nucleotide that mobilizes CALCIUM. It is synthesized from nicotinamide adenine dinucleotide (NAD) by ADP RIBOSE CYCLASE.Sperm Motility: Movement characteristics of SPERMATOZOA in a fresh specimen. It is measured as the percentage of sperms that are moving, and as the percentage of sperms with productive flagellar motion such as rapid, linear, and forward progression.Microinjections: The injection of very small amounts of fluid, often with the aid of a microscope and microsyringes.Acrosome: The cap-like structure covering the anterior portion of SPERM HEAD. Acrosome, derived from LYSOSOMES, is a membrane-bound organelle that contains the required hydrolytic and proteolytic enzymes necessary for sperm penetration of the egg in FERTILIZATION.Kelp: Large, robust forms of brown algae (PHAEOPHYCEAE) in the order Laminariales. They are a major component of the lower intertidal and sublittoral zones on rocky coasts in temperate and polar waters. Kelp, a kind of SEAWEED, usually refers to species in the genera LAMINARIA or MACROCYSTIS, but the term may also be used for species in FUCUS or Nereocystis.Vitelline Membrane: The plasma membrane of the egg.Nodal Protein: The founding member of the nodal signaling ligand family of proteins. Nodal protein was originally discovered in the region of the mouse embryo primitive streak referred to as HENSEN'S NODE. It is expressed asymmetrically on the left side in chordates and plays a critical role in the genesis of left-right asymmetry during vertebrate development.Species Specificity: The restriction of a characteristic behavior, anatomical structure or physical system, such as immune response; metabolic response, or gene or gene variant to the members of one species. It refers to that property which differentiates one species from another but it is also used for phylogenetic levels higher or lower than the species.Cloning, Molecular: The insertion of recombinant DNA molecules from prokaryotic and/or eukaryotic sources into a replicating vehicle, such as a plasmid or virus vector, and the introduction of the resultant hybrid molecules into recipient cells without altering the viability of those cells.Histones: Small chromosomal proteins (approx 12-20 kD) possessing an open, unfolded structure and attached to the DNA in cell nuclei by ionic linkages. Classification into the various types (designated histone I, histone II, etc.) is based on the relative amounts of arginine and lysine in each.Calcium Carbonate: Carbonic acid calcium salt (CaCO3). An odorless, tasteless powder or crystal that occurs in nature. It is used therapeutically as a phosphate buffer in hemodialysis patients and as a calcium supplement.Sequence Homology, Amino Acid: The degree of similarity between sequences of amino acids. This information is useful for the analyzing genetic relatedness of proteins and species.