Enlarge / Certain squid have the ability to camouflage themselves by making themselves transparent and/or changing their coloration. (credit: YouTube/KQED Deep Look )

Certain cephalopods like cuttlefish, octopuses, and squid have the ability to camouflage themselves by making themselves transparent and/or changing their coloration. Scientists would like to learn more about the precise mechanisms underlying this unique ability, but it's not possible to culture squid skin cells in the lab. Researchers at the University of California, Irvine, have discovered a viable solution: replicating the properties of squid skin cells in mammalian (human) cells in the lab. They presented their research at a meeting of the American Chemical Society being held this week in Indianapolis.

"In general, there's two ways you can achieve transparency," UC Irvine's Alon Gorodetsky, who has been fascinated by squid camouflage for the last decade or so, said during a media briefing at the ACS meeting. "One way is by reducing how much light is absorbed—pigment-based coloration, typically. Another way is by changing how light is scattered, typically by modifying differences in the refractive index." The latter is the focus of his lab's research.

Squid skin is translucent and features an outer layer of pigment cells called chromatophores that control light absorption. Each chromatophore is attached to muscle fibers that line the skin's surface, and those fibers, in turn, are connected to a nerve fiber. It's a simple matter to stimulate those nerves with electrical pulses, causing the muscles to contract. And because the muscles pull in different directions, the cell expands, along with the pigmented areas, which changes the color. When the cell shrinks, so do the pigmented areas.

Juvenile snapping shrimp now hold the acceleration record for a repeatable body movement underwater. They can snap their claws at accelerations on par with a bullet shot from a gun. (credit: Harrison and Patek, 2023)

The snapping shrimp , aka the pistol shrimp, is one of the loudest creatures in the ocean, thanks to the snaps produced by its whip-fast claws. And juvenile snapping shrimp are even faster than their fully grown elders, according to a recent paper published in the Journal of Experimental Biology. Juvenile claws accelerate as fast as a bullet shot from a gun when they snap, essentially setting a new acceleration record for a repeated movement performed underwater.

As we've reported previously, the source of that loud snap is an impressive set of asymmetrically sized claws; the larger of the two produces the snap. Each snap also produces a powerful shockwave that can stun or even kill a small fish. That shockwave produces collapsing bubbles that emit a barely visible flash of light—a rare natural example of sonoluminescence .

Scientists believe that the snapping is used for communication, as well as for hunting. A shrimp on the prowl will hide in a burrow or similar obscured spot, extending antennae to detect any passing fish. When it does, the shrimp emerges from its hiding place, pulls back its claw, and lets loose with a powerful snap, producing the deadly shockwave. It can then pull the stunned prey back into the burrow to feed.

Enlarge / Look at this lovely cube-shaped piece of poo, courtesy of the Australian bare-nosed wombat. (credit: Patricia J. Yang et al., 2021)

Scientists have been puzzling for decades over how the Australian bare-nosed wombat poops out neat little cubes of feces instead of tapered cylinders like pretty much all other animals. According to a new paper published in the journal Soft Matter, the secret lies in their intestines, which have varying stiff and soft regions that serve to shape the poo during the digestive process. Earlier preliminary findings by the same group won the 2019 Ig Nobel Physics Prize.

"Bare-nosed wombats are renowned for producing distinctive, cube-shaped poos. This ability to form relatively uniform, clean cut feces is unique in the animal kingdom," said University of Tasmania wildlife ecologist Scott Carver , a co-author on the paper. "They place these feces at prominent points in their home range, such as around a rock or a log, to communicate with each other. Our research found that these cubes are formed within the last sections of the intestine—and finally proves that you really can fit a square peg through a round hole."

Zoologist Eric Guiler first noted the unusual shape of wombat droppings in 1960, and to date, wombats are the only known animals to produce six-sided cube-shaped poo. It's one of several examples of naturally occurring pattern formation, such as the columns of Ireland's Giant's Causeway (formed by cooling lava), or how vibrating membranes can make grains of sand form " Chladni figures ." But naturally occurring cube shapes are extremely rare. The Australian bare-nosed wombat ( Vombatus ursinus ) can pump out as many as 100 cube-shaped droppings a day.

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