Jakarta –
Living things on Earth have a different number of legs. If humans have two legs, then spiders have four times that, that is, eight legs.
The number of spider legs is not without reason. Thomas Hegna, an assistant professor of invertebrate paleontology at the State University of New York, explains that the reason spiders have many legs comes from their ancestors.
“I think the best answer and the simplest answer is that spiders have eight legs because their parents did,” Hegna told Live Science.
Spider Ancestor
The ancestry of spiders goes back about 500 million years. During the middle Cambrian Period, lived the lineage chelicerates, the group of arthropods that includes spiders. But if we go back even further to 541 million years, there would be a species called lobopod that lived in the oceans, the ancestor of all arthropods.
The name “lobopod” refers not to one species but to a wide variety of species. Basically, they are worm-like creatures with segmented bodies. Each segment features an identical pair of short, stubby legs.
As lobopods evolved, they began to specialize in legs and fused body segments. Early chelicerates had fused their small body segments into two large parts: head and abdomen.
Scientists still don’t know why, but the head retained the legs, and the lobopod abdomen lost the legs. By the time spiders appeared 315 million years ago, they had inherited a body shape that was perhaps 150 million years old.
“The leg is actually part of their mouth,” says Nipam Patel, a developmental biologist and director of the Marine Biology Laboratory, affiliated with the University of Chicago.
Spiders, insects, crustaceans and millipedes all evolved from ancestors who likely had segmented bodies. According to Patel, all arthropod appendages including the legs, antennae, and even the mandibles (jaws), can be traced back to the original body of the lobopod.
Why Spiders Have Many Legs
Heather Bruce, a research associate at the Marine Biology Laboratory, said that initially all lobopods had the same legs. Until, the leg increases and has another function.
“Originally, all the legs were the same,” says Heather Bruce.
“But then the feet first serve as sensory appendages, such as for tasting and grabbing food.”
Since then, the ancestors of chelicerate spiders began to diverge from other groups. In the ancestors of insects and crustaceans, the dual-functioning forelimbs of the lobopod lost its prey-catching ability and became specialized sensory structures called antennae.
The second pair of legs of the chelicerates evolved into a single set of appendages called pedipalps. The next four pairs of legs remain in the role of walking legs.
Watch the video “Results of Separation of Six-Legged Babies at NTB Hospital”
(nir/nwk)
2023-08-06 08:00:00
#Spiders #Legs #History
