Sea spiders have always been shrouded in a bit of a mystery in the scientific world. Technically, sea spiders are not spiders at all, considering they breath underwater by trapping air around its abdomen. Even though this is a biological oddity, there is one more that is worth mentioning – sea spiders have sex with their legs.
There are over 1,300 species of sea spiders that have been classified in the animal kingdom. Though, scientists are perplexed by its anatomy, causing them to be unsure of how to classify it. The problem is that these creatures are among the oldest species living on Earth. These types of spiders are said to have evolved into what they are today over 500 million years ago, branching off early from an evolutionary period of marine arthropods. It is evident to scientists that this type of spider is anatomically different from anything else, including their mating rituals.
Currently, sea spiders have been grouped with other joint-legged invertebrates, such as horseshoe crabs, ticks, and any other type of spider. They have claw-like mandibles known as chelicerae, inferring they should be classified in the subphylum Chelicerata. They live in both deep and shallow seas all over the world. The creatures are carnivores, feeding on nearly anything that is stationary, like corals and sponges. Though, sea spiders can also engage in a more advanced form of hunting when tracking worms or sea slugs.
Although sea spiders are different from others in its phylum, the way in which they have sex is like nothing that has ever been seen before. Their acrobatic fornication shows they could be one of the most interesting animals on the planet.
The genitals of the sea spiders are located on its legs. Since the thorax of the body is small and slender, most of its vital organs cannot fit in its body cavity. Therefore, their entrails, as well as their genitals, extend down into their tall, slinky legs. Such a peculiar anatomical characteristic makes for a very interesting procreation method.
The long-legged tripod-like animals are, according to scientists, masters of acrobatic sex. Sea spiders have genital pores located up and down their legs. While the male only has genital pores on two of its legs, females have them on all eight legs. These pores act like openings that can be accessed when the mating ritual begin. When couple goes to mate, the male climbs up the female, which is twice his size, clinging onto the underside of her body she is while standing still. Afterwards, their respective pores come into contact for the female to release eggs. When the eggs come in contact with the male’s sperm they create spherical bundles of fertilized embryos.
As the larvae begin to grow, the male holds onto the bundles with additional appendages that act as arms, known as baby björns ovigers. Moreover, just like sea horses, the male sea spiders carry the larvae. He will carry the eggs until every one hatches, and ferry the young about on his back.
The way in which sea spiders have sex shows that there are many odd ways evolution has influenced the procreation method. This leaves scientists wondering if any other creatures in the animal kingdom have sex in uncanny ways.
By Alex Lemieux
Wired: Absurd Creature of the Week: This Isn’t a Spider, But It Does Have Genitals in Its Legs
NCBI: The genetic mating system of a sea spider with male-biased sexual size dimorphism: evidence for paternity skew despite random mating success
EOL: Sea Spiders
Photo Courtesy of Asbjørn Hansen’s Flickr Page – Creative Commons License
Photo Courtesy of Sylke Rohrlach’s Flickr Page – Creative Commons License