Ordo Notostraca

    Triops cancriformis
Occurring in England and Scotland at single sites each.

Ordo Anostraca

    Chirocephalus diaphanus
Occurring in England, restricted to Devon, Cornwall, the New Forest, Wiltshire and Cambridgeshire (at the northwestern limits of this species )

According to: Alan Rose, thank you for the information! For information on Ch. diaphanus, thanks to Ian Perkins.