Sea Star Life Cycle

Animals are multicellular, heterotrophic eukaryotes that obtain nutrients by ingestion. Ingestion means eating food. Most animals are diploid and reproduce sexually. Male and female adult animals make haploid gametes by meiosis, and an egg and a sperm fuse, producing a zygote. The zygotes divides by mitosis, forming an early embryonic stage called a blastula, which is usually a hollow ball of cells. In the sea star and most other animals, one side of the blastula folds inward, forming a stage called a gastrula. The internal sac formed by gastrulation becomes the digestive tract, lined by a cell layer called the endoderm. The embryo also has an ectoderm, an outer cell layer that gives rise to the outer covering of the animal and, in some phyla, to the central nervous system. Most animals have a third embryonic layer, known as the mesoderm, which forms the muscles and most internal organs. After the gastrula stage, many animals develop directly into adults. Others, such as the sea star, develop into one or more larval stages first. A larva is an immature individual that looks different from the adult mammal. The larva undergoes a major change of body form, called metamorphosis, in becoming an adult capable of reproducing sexually. Biology book pg 366

 

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