Slipper limpets are unique because their sexual development is influenced by touch with other individuals of the same species. Maryna Lesoway from the University of Illinois at Urbana Champaign concisely explains current research on the phenomenon.
Video: Touch-Based Sex Determination in Slipper Limpets
Image shows several slipper limpets (small snail-like organisms) with four captions reading (1) A larva that settles on an unoccupied substrate develops into a female, which produces chemicals that attract other larvae. (2) The larvae attracted by the female settle on top of her and develop into males, which become mates for the original female. (3) Eventually the males on top switch sex, developing into females. (4) They then attract additional larvae, which settle on top of the stack and develop into males. This image is from Genetics: A Conceptual Approach, Fourth Edition.