A new species of microconchid tubeworm, Microconchus cravenensis is described from the Mississippian Cracoean reefs of North Yorkshire, United Kingdom. Despite the fact that some other microconchid species could have attained large tube length, the new species possesses the largest recorded diameter (to 7.7 mm) of the planispirally-coiled (attachment) tube and the largest recorded aperture diameter (8.3 mm) in the helically uncoiled portion. Thus, with respect to these features, Microconchus cravenensis n. sp. is the largest and most robust microconchid species recognized so far. At present, it is only known from the Craven Reef Belt of North Yorkshire, where it attached to corals and possibly bivalve shells, and was preyed upon by small durophagous animals, as indicated by repaired injuries preserved on one of the tubes.