  Fermi arc states are features of Weyl semimetal (WSM) surfaces which are
robust due to the topological character of the bulk band structure. We
demonstrate that Fermi arcs may undergo profound restructurings when surfaces
of different systems with a well-defined twist angle are tunnel-coupled. The
twisted WSM interface supports a moir\'e pattern which may be approximated as a
periodic system with large real-space unit cell. States bound to the interface
emerge, with interesting consequences for the magneto-oscillations expected
when a magnetic field is applied perpendicular to the system surfaces. As the
twist angle passes through special "arcless angles', for which open Fermi arc
states are absent at the interface, Fermi loops of states confined to the
interface may break off, without connecting to bulk states of the WSM. We argue
that such states have interesting resonance signatures in the optical
conductivity of the system in a magnetic field perpendicular to the interface.
