Animal Rips Apart Own Skin Before Meals

Eating is no small task for freshwater hydra, which have to rip open their mouth cells to take in food.

Tiny freshwater animals known as hydra must rip open their mouth skin in order to eat, and now new research shows how they manage to do this.

The unusual process involves changes to the hydra's mouth skin cells that allow the creature to stretch and split apart these cells in a dramatic deformation. The findings are published in the latest issue of the Biophysical Journal.

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"The fact that the cells are able to stretch to accommodate the mouth opening, which is sometimes wider than the body, was really astounding," senior author Eva-Marie Collins said in a press release. "When you watch the shapes of the cells, it looks like even the cell nuclei are deformed."

Collins, who is a biophysicist at the University of California, San Diego, and her team genetically engineered hydra so that the animals' two layers of tissues would light up, revealing how their mouths and bodies work on a cellular level.

Hydra measure less than one half an inch long. They look like a column with a ring of tentacles at the end. In the wild, the other end adheres to a rock or some other kind of surface, keeping the hydra in place while it waits for unsuspecting prey to swim by.

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When a potential victim, such as a small shrimp, brushes against the hydra's tentacles, the predator shoots out poisoned barbs to sting and paralyze its prey. Once the hydra contracts its tentacles, a special group of cells splits apart to display the black interior of its mouth, and the hydra sucks the prey in.

When the meal is digested, the hydra rips open its mouth to spit out any leftover materials. It then seals it back up into a continuous sheet of tissue, and waits for the next shrimp or other victim to swim by.

In the below video, a hydra in a lab eats a small crustacean, showing what the hunting and feasting look like from farther away:

click to play video

Small Worlds Never Before Seen: Photos

The lit tissues of the genetically engineered hydra showed that the animal's cells change their shape, rather than move around, when the mouth opens.

"We can try to understand what look like very complicated processes in the living animal with relatively simple physics," Collins said.

She and her team next determined that once triggered, radially oriented fibers in the hydra's tissue contract to stretch the cells apart, similar to how muscles in the iris contract to open our pupils. When the researchers added magnesium chloride to act as a muscle relaxant, the hydras couldn't open their mouths at all.

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No other species on Earth is known to feed in such an unusual manner.

Collins asked, "Evolutionarily, why do these animals have this weird mechanism for feeding? We don't really have an answer for that, but it's a really interesting question."

The scientists are trying to answer it now by investigating what physiological consequences the shape-changing might have for hydra's cells.

Hydra vulgaris is shown opening its mouth.

Oct. 23, 2012 --

For 37 years the Nikon Small World photography competition showcases the beauty and extreme details captured using light microscopes. Every year the world below the waves provides many interesting subjects for the Small World competition. Most examples of aquatic life are entered by professionals in, or students of marine biology, but many of these images were provided by entrants from other disciplines who simply find marine life fascinating. Here, photomicrographer Arlene Wechezak of Anacortes, Wash., and 10th place winner of the 2009 Small World Contest, magnified 10x an Obelia species of hydrozoa with extruded medusae as a fresh sea water mount using a darkfield.

Here we see the same species as before only this time magnified 40x its original size. The extruded medusae of the Obelia hydrozoa contain tentacles that sting and capture the animal's prey.

In this image, biologists magnified 20x a species of bryozoan of the genus Membranipora found on seaweed and kelp using stereomicroscopy.

Almost transparent tissue covers the hard skeleton "cups" of each polyp in this brightfield photo of brain coral in the genus Goniastrea magnified 25x.

Marine biologist Alvaro Migotto of the University of São Paulo in Brazil used stereomicroscopy and a darkfield to capture this photo of a brittle star magnified 8x.

Photographer David Maitland of Feltwell, UK, zoomed in with 100x magnification on coral sand over a brightfield.

Surface of shark skin tanned with a chromium compound magnified 40x with reflected light.

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On its side this marine ciliate (Rhabdonella spiralis)looks like a trumpet; when the image is turned vertical it looks like a champagne flute - a fine photo from French oceanographer John Dolan, who used a differential interference contrast technique and 40x magnification.

A freshwater Bryozoan, or moss animal, Cristatella mucedo in a darkfield magnified 6.5x.

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Biologist Diana Lipscomb of George Washington University in Washington, used Nomarski Interference Contrast and a magnification of 400x the original size to showcase a suctorian ciliate, Acineta tuberosa, in the phylum Ciliophora.

Using Nomarski Interference Contrast and a magnification of 400x the original size this photo shows a ciliate in the genus Sonderia that preys upon various algae, diatoms, and cyanobacteria.

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Algae magnified 400x using a confocal technique. (Algae genus: Staurastrum, Kirchneriella, Akistrodesmus and Microthamnion)

PHOTOS: Small Worlds Never Before Seen