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Bizarre prehistoric arthropod had its own built-in cutlery to chow down on dinner with

By Elizabeth Rayne
Alice the shrimp from Deep

Anyone who eats shrimp or lobster probably doesn't use a knife and fork, but there was once a species of shrimplike marine arthropod that brought its own to dinner.

Xiaocaris luoi (possibly a relative of Alice from Deep, above?) is a newly discovered species of prehistoric arthropod first misidentified as the species Jianshania furcatus. It floated around in Cambrian seas 518 million years ago, around the time that the Cambrian explosion spawned all sorts of strange new life-forms. This tiny but fierce creature also had a staggering 800 pieces of cutlery built into its body. Each of its 54 legs that each had up to 15 spines that looked like serrated knives, and when not in use for at its restaurant of choice (whatever fell to the seafloor for this scavenger), they carried it through the ocean in a perpetual wave motion kind of like a sea monkey. Talk about bringing your silverware with you.

"Xiacoaris is a type of arthropod (animals with jointed limbs and articulated exoskeletons) known as a fuxianhuiid, which include more than half a dozen species that are only known from the early Cambrian of China," paleontologist Javier Ortega-Hernández, who recently published a study in BMC Evolutionary Biology, told SYFY WIRE. "Xiaocaris and other fuxianhuiids are regarded as particularly distant relatives of the arthropods that we can see today, like spiders, shrimp and insects, and indeed they tell us a lot about how the species that live with us today evolved half a billion years ago. The legs of Xiaocaris are an interesting puzzle because they have quite a few more segments that the legs of most arthropods, but it is difficult to be sure if they look like this because they are primitive, or because they are highly specialized for their particular ecology.

Unearthing this creature in the Chenjiang Biota in China’s Yunnan province was no surprise to the team, since that region is known to be overflowing with preserved sea creatures, especially anything with a shell. It is almost like an underwater view of the Cambrian Explosion frozen in time. Some have even been found with soft tissue still intact.

The boomerang-headed X. luoi had the hard outer shell, or sclerite, characteristic of arthropods. The sclerite was made up of tergites, or armored plates covering the back of an arthropod with the exception of the head. Its tail was split into two lobes, or flukes. There were ridgelike structures otherwise known as a dorsal keel on its abdomen and the backs of its antennae, and apparently was the type to go big or go home, since those antennae each had 18 segments. 

"The antennae of Xiaocaris, and other fuxianhuiids and arthropods more generally, tend to be elongate because these limbs fulfill an important sensorial function. These animals would have lived close to the sea bottom, were sediment can murky the waters, so it would be important for them to have another way of sensing their environment in addition to their eyes," Ortega-Hernández said.  

This all sounds quasi-normal until you get to its leg equipment.

Scavengers don’t always have the most conventional ways of feeding. You have zombie worms, and then you have isopods, or those huge lilac pill bugs that demolished an alligator carcass at warp speed, with some help from their odd menagerie of friends, such as shrimplike amphipods and bug-eyed grenadiersX. luoi would have been the star of this freakshow if it was still around. To see it in action must have been like watching an extremely skilled knife juggler.

When it came upon the soft tissue of a deceased animal at the bottom of the ocean, X. luoi broke out all 800-something of its legs and started shredding. This made it much easier for the creature to devour food right there (and also didn’t require it to just hang out hungry until particles of something came floating by). They may have not had the sharp and menacing mouthparts of extant isopods, but they sure made up for it with all those appendages. The team used CAT scans to get an unprecedented look at X. luoi’s legs. Look closely and you will start to see the resemblance to steak knives.

So why did all those legs vanish over time? While arthropods such as centipeds and millipeds are widely known in both science and horror movies as having seemingly endless appendages, the future iterations of X. luoi evolved out of them.

"There is a fascinating overall evolutionary trend with arthropods in which some of the earliest members of this group, such as fuxianhuiids, which have a lot of legs, but with time these become fewer and fewer," explained Ortega-Hernández. This is well exemplified with insects, which only have six pairs of walking legs. Generally speaking, arthropods have modified their legs quite heavily to perform different functions, such as feeding, cleaning and mating. Because fuxianhuiids are so ancient, they only have a limited degree of leg specialization, particulary when compared to some of the groups we see today. 

X. luoi was outlandish even for an athropod that surfaced during the Cambrian Explosion, but many creatures that were first seen during this period ended up being the ancestors of more familiar things. This arthropod doens't have any direct descendants. It was most closely related to fuxianhuiids, which lived in the seas of China some 500 million years ago and all of which are extinct. It distantly makes a connection to extant arthropods like shrimp and other crustaceans and arthropods. You wouldn't even be able to shell and eat X. luoi like a shrimp. You can do away with most of the shell of a shrimp pretty easily becuase the head is fused to about a third of its body. X. luoi's head was unfused. Good luck with that.

"Xiaocaris is as related to a living shrimp as a Triceratops is related to a hummingbird, which is to say that they certainly belong to the same large family tree but are quite distant from each other! Many of the changes that eventually led to the evolution of shrimp and other crustaceans considering that Xiaocaris and other fuxianhuiids represent their distant ancestors include the specialization of the legs for different functions, the appearance of a complex head region, and the fusion of several body segments to form specific body regions," Ortega-Hernández said.

This can only make you wonder what else is lurking in the Chenjiang Biota—and what kind of alien morphology it might have had.

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