As with all Phallostethus—"penis chest" in Greek—species, the male uses its bony "priapium" to clasp a female while he inserts sperm into her urogenital opening, also located on the head, said Lynne Parenti, curator of fishes at the National Museum of Natural History in Washington, D.C.

Parenti remembers seeing another species of priapiumfish mate at a lab in Singapore. Attached at the head and together forming a v, the fish "looked like a little pair of scissors, darting around the tank together," she said.

For many fish, such as guppies, mating is almost instantaneous, but priapiumfish "actually couple, staying together for a remarkable period of time," she noted.

(See "Weird New Ghostshark Found; Male Has Sex Organ on Head.")

The new species