Originally native to the Atlantic coast of North America, this hydroid has hitched rides on ships, to California, Australia, the Mediterranean Sea and South America. It was found in California as early as 1859. Eggs are held back in the parent, then chemicals are released by the parent to attract the sperm for fertilization. The larval medusae stage (classic jellyfish appearance) of their life cycle, is retained in the parent until it matures to the stage where it then works its way out of the parent (planula stage). It eventually becomes a free swimming larvae (actinula) resembling the adult before it settles down, often nearby.
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