Sexual selection (essentially the competition for mates) is traditionally studied in highly mobile organisms with complex behavioural repertoires, sophisticated visual systems, and obvious adaptations that function in the context of increasing reproductive fitness. It is far less obvious how sexual selection operates in organisms that are immobile (e.g. clamped to the seabed) and release gametes seemingly haphazardly into the external environment (i.e. sessile or sedentary external fertilizers). Indeed, Charles Darwin comically dismissed the possibility of sexual selection in such taxa in his original treatise of the topic, arguing that these organisms have ‘too low mental powers’ to be capable of the subtleties of mate choice and mating competition. The aim of this talk will be to convince you otherwise. I will summarise a series of playful experiments on mussels and sea urchins that led to the observation that these taxa exhibit sophisticated processes of sperm-egg interaction that ultimately facilitate sexual selection at the level of the gamete. Our work on these systems has revealed preliminary insights into the complex patterns of selection on ejaculates and tantalizing evidence that eggs release subtle variations in chemical signals that may facilitate the fusion of genetically compatible gametes. I’ll end the talk with some inevitable speculation on the mechanisms that might drive these processes, with the firm hope that someone far more qualified than me will put me on the right track.