SCIENCE -ROMANCE LAB- SCENES : DEEP-SEA ALLURE

'' For underwater romance - a toothy forehead. '' Life in the ocean can be lonely, especially for a male chimaera. So when one of the creatures finds a mate, he holds her close.

To do this, a male chimaera, also known as ratfish or ghost shark, uses a fleshy appendage sticking out of his forehead. It's called a tenaculum, and it grips the female's pectoral fin during mating.

If that sounds strange, it gets stranger : The bulbous end of this forehead grip is studded with structures that amount to teeth. How chimaeras evolved such a strange feature has long puzzled biologists.

'' We haven't seen anything like this anywhere else in the animal kingdom, period,'' said Gareth Fraser, an evolutionary biologist at the University of Florida.

In a new paper, Dr. Fraser's team reveals that the structure is covered in rows of teeth similar to the jaws of a shark. Chimaeras are cartilaginous fish like sharks, but only distantly related. The two groups diverged 400 million years ago, and chimaeras largely lack other sharklike traits, including scales and sharp teeth.

One distinguishing feature is the tenaculum, which houses those forehead teeth and is also called a head clasper. The clasper sits inside a pocket above the fish's eyes when not in use. Beyond its basic function, little was known about how the structure developed or whether it was covered by teeth or skin features.

Dr. Fraser's team used micro-CT scans on 40 ratfish specimens to track the tenaculum's growth from a pimplelike projection in juveniles to the fully formed club on adult males.

The budding toothlike structures proved to be actual teeth with mineralized tips. The researchers also examined fossils of prehistoric chimaeras and their relatives.

Dr. Fraser posits that even as the tenaculum moved away from the fish's jaws over the eons, chimaeras retained their ability to form sharklike teeth, helping them dole out love bites to prospective mates.

The World Students Society thanks Jack Tamisiea.