Cats may bite, and geese may have barbed penises, but one newly described hermaphroditic sea slug has taken violent animal sex to a new level by stabbing its mates in the head.
The perpetrator of this bizarre act, Siphotperon sp. 1, is a small sea slug found off the northeast coast of Australia. A simultaneous hermaphrodite, it has both male and female reproductive organs that it uses simultaneously during sex.
For its male organ, the slug has a two-pronged penis consisting of a penile bulb that transfers sperm, and a separate, needlelike appendage called a penile stylet that stabs and injects partners with prostate fluid-containing sex hormones called allohormones.
This stabbing behavior, known as traumatic secretion transfer, is fairly common amongst hermaphroditic sea slugs, and does not actually traumatize the slug — the term trauma refers to the Greek translation as “wound.” The behavior is well documented, but still not very well understood. It is thought to help individuals increase reproductive success by either inhibiting fertilization by others or increasing fertilization by their own sperm, but this remains unclear.
Researchers have also noted that different species, and even members within the same species, stab mates in different regions of the body, raising the question of how these individuals decide where to aim their shots.