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Sea Spiders: Pycnogonida

Behavior And Reproduction

The habits of most sea spiders are poorly known. Some longer-legged species are good swimmers, but most sea spiders prefer to crawl about colonies of anemones, corals, and other stationary, or unmoving, prey animals, or animals that are their source of food.

Most species have both males and females, but in at least one species each spider has the reproductive organs of both sexes. In the few species of sea spider that scientists have studied, courtship, or the activity meant to attract a mate, is brief. While mating, the male and female are positioned so that they are belly to belly, head to tail.

As the female lets go of her eggs, the male releases sperm into the water over them. He then collects the fertilized eggs into a ball and attaches them to his egg-carrying structures with special "glue." Males usually mate with more than one female and are often seen carrying several batches of eggs, each batch the result of a different mating. Males typically carry the eggs until they hatch. Young seas spiders, or larvae (LAR-vee), usually swim freely in the ocean. Most species gain more pairs of legs as they grow into adulthood, although some hatch from the egg with a complete set of legs.


The name Pycnogonida comes from the Greek words pyknos, meaning "thick" or "knobby," and gony, or "knees." These animals are called sea spiders because of their similarity to true spiders. Fossil (FAH-suhl) sea spiders, the remains of animals that lived long ago, date back almost four hundred million years. Even without fossil evidence, scientists studying living sea spiders are convinced that these animals are among the world's oldest groups of animals. There are about one thousand species of sea spiders worldwide. Although sea spiders were first discovered nearly 150 years ago, very little is known about them, especially those species living at great depths in the sea. Their unusual body form has made it difficult for scientists to figure out just how they are related to other arthropods. They are most closely related to horseshoe crabs and spiders and their relatives.

Additional topics

Animal Life ResourceInsects and SpidersSea Spiders: Pycnogonida - Physical Characteristics, Habitat, Diet, Behavior And Reproduction, No Common Name (colossendeis Megalonyx): Species Account - GEOGRAPHIC RANGE, SEA SPIDERS AND PEOPLE, CONSERVATION STATUS