Video of mating behaviour: "mate guarding" is where the male latches on to the female's carapace (shell) (they have special claspers to do so) and holds on to her until she moults. when the female moults her carapace is soft and he has easy access for insemination.
Thanks Claire Sives for ID and brief explanation
For more information Ref:
Benvenuto, Chiara C, Stephen C Weeks and Brenton Knott, ‘Mate-Guarding Behavior in Clam Shrimp: A Field Approach’ (2009) 20(5) Behavioral Ecology 1125.
Zandra M S Sigvardt and Jørgen Olesen, ‘Mating Behaviour in Laevicaudatan Clam Shrimp (Crustacea, Branchiopoda) and Functional Morphology of Male Claspers in a Phylogenetic Context: a Video-Based Analysis’ (2014) 9(1) PLoS ONE e84021