Some young sea spiders can regenerate significant portions of their bottom halves, including muscles, reproductive organs, and the anus, or can function without them, according to a study published on January 23rd in the Proceedings of the National Academy of Sciences.
The ability to regrow body parts is not widely seen, but some species possess this capability. For example, some sea slug heads can regenerate their entire bodies, and sea spiders and other arthropods can regrow parts of their legs. Researchers previously believed that arthropods could only regenerate legs, possibly due to their hard exoskeletons preventing them from regenerating other body parts.
Evolutionary biologist Georg Brenneis of the University of Vienna first discovered that sea spiders (Pycnogonum litorale) might have the ability to perform more complex regenerations when he accidentally injured a young specimen in the lab with forceps. The specimen was still alive despite being injured, so he decided to observe it.
Regeneration Ability of Spiders
Several months later, he noticed that the sea spider had grown an extra leg instead of a scar in place of the injury. This discovery was later reported in 2016 in The Science of Nature by Brenneis and evolutionary biologist Gerhard Scholtz of Humboldt University of Berlin. In a recent study, researchers amputated parts of the lower halves of 19 young sea spiders, and most of them were able to regrow the missing muscles and other parts. However, the regeneration was not always perfect, as some juveniles ended up with six or seven legs instead of eight.
None of the four adult sea spiders could regenerate the amputated body parts. According to Brenneis, this may be because adults do not shed their skin as they grow, indicating that regeneration and molting may be connected. Additionally, two young sea spiders did not regenerate at all, but instead of dying, they survived with only four legs and without an anus. These sea spiders could excrete waste through their mouths by regurgitation, as per Science News.
The next step for the researchers is to determine if other arthropods can regenerate more than previously thought and to understand the mechanisms behind the sea spiders' regenerative capabilities. Brenneis says that she would like to see how it works. Scientists have long been puzzled by the phenomenon of marine animals that live in the deep sea and polar oceans reaching large sizes in these environments but not in others.
The adult sea spider (Pycnogonum litorale) in this microscope image fully recovered after its back half was amputated, showing that arthropods can regrow more body parts than scientists realized.
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Spidering From Land to Water
To understand this, Caitlin Shishido, a Ph.D. student at the University of Hawaii at Manoa, and Amy Moran, a researcher at UH and the University of Montana, headed to Antarctica to test the 'oxygen-temperature hypothesis', which suggests that animals living in extreme cold can grow to giant sizes due to their slow metabolisms.
They focused their study on sea spiders, marine relatives of land spiders who breathe through their legs. The study was published in the Proceedings of the Royal Society of London and was conducted at McMurdo Station, Antarctica, and UH. According to Shishido, capturing oxygen and bringing it to cells is a huge task for animals, and it's even bigger for large animals than for small ones. Shishido concluded that anyone could grow to a large size if cold temperatures make them require less oxygen.
Speaking of spiders, Science Times reported that the Huntsman spider family, Sparassidae, comprises 1,383 known species, and the Giant Huntsman spider is the largest among them. They are known for their large leg span and are called "huntsman" because of their quick movement and hunting behavior. They are sometimes referred to as crab or wood spiders, but they have no relation to baboon spiders, per Australian Museum. The largest Huntsman spider recorded had a leg span of around 11 inches, but on average most species have a leg span of 5 inches or less. Despite their large size, they are not aggressive toward humans and are known for their docile and gentle nature.
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