Pycnogonids are small marine arthropods, commonly known as sea spiders, which belong to the phylum Arthropoda. There are several synonyms for the term pycnogonids including Pantopoda, Pycnogonacea, sea spiders, and sea walnuts. These synonyms are used interchangeably to refer to the same group of animals. Pycnogonids are characterized by their elongated bodies, long legs, and distinctive proboscis that is used to capture prey. These animals are found in oceans all over the world and play an important role in the marine ecosystem. Despite their eerie appearance, pycnogonids are harmless to humans and are often used as model organisms in scientific research.