Friday, July 26, 2013

Pyura Chilensis - The Living Rock

Pyura chilensis, called piure in Spanish, is a tunicate of the family Pyuridae. It was described in 1782 by Juan Ignacio Molina.

Pyura chilensis is a tunicate that resembles a mass of organs inside a rock. It is often found in dense aggregations in the intertidal and subtidal coast of Chile and Peru. It is a filter feeder that eats by sucking in seawater and filtering out microorganisms. P. chilensis has some basic characteristics common to chordates, such as the notochord and a perforated pharynx. It is born male, becomes hermaphroditic at puberty, and reproduces by tossing clouds of sperm and eggs into the surrounding water. If it is alone, it will procreate by self-fertilization.

Its blood is clear and contains high concentrations of vanadium, which may be ten million times that found in surrounding seawater; although the source and function of these mineral concentrations are unknown.

On the Chilean coast, banks of P. chilensis are heavily fished. The animal is also one of the main food sources for other local aquatic species such as the Chilean abalone (Concholepas concholepas), whose proliferation has threatened P. chilensis and severely restricted its growth for more than two decades. Many locals don wet suits and goggles to gather the delicacy, mostly in rocky areas close to shore, but occasionally farther out to sea, mindful always of the dangers of the Chilean Pacific.

Fishermen typically cut P. chilensis into slices with a handsaw, then use their fingers to pull out the siphons (which they refer to as tetas, or "titties") from the carapace, which is discarded. The flesh is usually sold in strips, but may be canned. It is exported to numerous countries, including, as of 2007, Sweden (32.5% of exports) and Japan (24.2%). 

The meat, which has a strong flavor and is considered very tasty, can be eaten raw or cooked. It is usually cut into small pieces, and flavored with chopped onion, cilantro, and lemon. Minced and boiled, it serves as an element of many dishes, particularly arroz con piure picado, or "rice with minced piure”. It can also be fried and eaten on bread.

There are concerns about the safety of eating P. chilensis, given its high concentration of vanadium. Vanadium is a heavy metal, considered toxic at any more than incidental levels. The average diet provides trace amounts of vanadium; typically 6-18 micrograms (mcg). According to the University of Maryland Medical Center, vanadium can cause liver damage in high doses of 1.8 mg or more daily. No in-depth studies have been done to determine the amount of vanadium contained within the blood or tissue of P. chilensis, nor in typical dishes containing its flesh, so it cannot be considered safe.

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