Silk spinners and spidery male sex organs mix with nonspider traits
What looks like a spider, but with a segmented rear plus a long spike of a tail, has turned up in amber that’s about 100 million years old.
Roughly the size of a peppercorn (not including the tail, which stretches several times the body length), this newly described extinct species lived in forests in what is now Myanmar during the dinosaur-rich Cretaceous Period.
Spiders as their own distinctive group had evolved long before. Whether this tailed creature should be considered a true spider (of the group Araneae) is debatable though, researchers acknowledge February 5 in two studies in Nature Ecology & Evolution. In one of the papers, the fossils’ chimeric mash-up of traits both spidery and nonspidery inspired Bo Wang of the Chinese Academy of Sciences in Nanjing and colleagues to name the species Chimerarachne yingi.
C. yingi indeed has some anatomy that, among living animals, would be unique to spiders, says Gonzalo Giribet of Harvard University, a coauthor of the other paper. The fossils have what look like little structures that could have exuded spider silk, as well as distinctive male spider sex organs. Called pedipalps, these modified legs have no direct connection to a sperm-producing organ. Spiders need to load them before mating, for instance by ejaculating a sperm droplet and dipping pedipalps in it, so the structures can deliver the sperm a bit like a syringe.
But the abdomen-like end of a true spider’s body isn’t segmented and certainly doesn’t have a tail. Giribet and his colleagues’ analysis puts C. yingi in an ancient sister group of spiders. That’s startling in itself, Giribet says, because researchers have speculated that this Uraraneida group had gone extinct much earlier. So, spider or not, C. yingi remains intriguing.
B. Wang et al. Cretaceous arachnid Chimerachne yingi gen. et sp. nov. illuminates spider origins. Nature Ecology and Evolution. Published online February 5, 2018. doi: 10.1038/s41559-017-0449-3.
D. Huang et al. Origin of spiders and their spinning organs illuminated by mid-Cretaceous amber fossils. Nature Ecology and Evolution. Published online February 5, 2018. doi:10.1038/s41559-018-0475-9.
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