Fishy origin of remora's shark-sucking hat

Julia Sklar, reporter

(Image: Dave Johnson)

This spectacular headpiece isn't the latest head-turning fashion in hats. Instead, this remora is sporting the feature that gives the fish its nickname, "sharksucker": a sucking disc on top of its head, allowing it to benignly attach itself to other sea creatures.

The disc's ribbed appearance gives a clue to its intriguing origin: the sucker develops from the same larval bones that grow into dorsal fins in other species, despite their drastically different shapes on the adult fish.

By using a red dye to stain the bones of larval remoras, researchers were able to track the growth of what would become the sucking disc. At the same time, they followed the development of dorsal bones in a different kind of fish. They noticed that the dorsal fins and sucking discs developed in exactly the same way in both animals, up to a certain point. ?

The pivotal moment comes when the bones of the remora's dorsal fin begin to expand and inch forward, towards the head.? By the time the fish is 30 millimetres long, the dorsal fin bones have become a fully formed sucking disc about 2 millimetres long. Inside, the sucker keeps many structures in common with a dorsal fin, with minuscule fin spines and supporting bones. However, the remora's bones underpin movable slats that open and close to create suction.

Ralf Britz of the Natural History Museum in London, who worked on the study, said the sucker reminded him of Linnaeus's observation of nature's magnificent ability to recycle useful parts.

"What keeps impressing me when I study the development of some of the weirdest structures in the fish world is that natura non facit saltus, "nature does not make jumps", and even the strangest anatomical modifications happen through small gradual changes in development," Britz says.

In 2006, Britz was a member of the team that discovered the world's smallest vertebrate, the Sumatran fish Paedocypris progenetica, which also flaunts an unusual gripping fin.

Journal reference: Journal of Morphology, DOI: 10.1002/jmor.20105

Source: http://feeds.newscientist.com/c/749/f/10897/s/28241669/l/0L0Snewscientist0N0Cblogs0Cshortsharpscience0C20A130C0A20Cfishy0Eorigin0Eof0Eremora0Bhtml0Dcmpid0FRSS0QNSNS0Q20A120EGLOBAL0Qonline0Enews/story01.htm

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