Arthritica bifurca (Webster, 1908)
Width 6mm, Height 5mm
Marine, Recent, Fossil, Native - Endemic
North Island and northern South Island as far south as Banks Peninsula, from 0-72m

Arthritica crassiformis Powell, 1933
Width 5.5mm, Height 4.5mm
Marine, Native - Endemic, Commensal upon the pholad, rock boring Anchomasa, usually found around the base of the siphon and along the lower mantle edges
North-eastern and south-western North Island and northern South Island as far south as Cape Campbell. Intertidal, from 0m

Arthritica hulmei Ponder, 1965
Width 3.4mm, Height 2.8mm
Marine, Native - Endemic, Commensal with a large polychaete worm, the seamouse, Aphrodita australis
Northern north-western, north-eastern and south-western North Island and northern South Island as far south as Cloudy Bay, from 0-132m