The males of this species have a phallic organ which moves  either to the left or the right.
The males of this species have a phallic organ which moves  either to the left or the right. The females' genital opening is  similarly affected, and as a result, a left-directed male can mate  only with a right-directed female, and vice versa. FTP name these,  any of three species of fish, which are commonly referred to as  "four-eyed" fishes.
The males of this species have a phallic organ which moves  either to the left or the right.
{anableps}