Maurea granti, also known as Grant's top shell, is a species of sea snail, a marine gastropod mollusc, in the family Calliostomatidae. Endemic to New Zealand, the species is found offshore up to depths of . It is a polymorphic species, with different shell thickness, colour and spiral cord numbers appearing in shallow water and deep water specimens.
In the original description, Powell described the species as follows:
The holotype of the species has a height of , a diameter of , and a thickness of , and a spire angle of 62ð. The species has a maximum height of and diameter of .
The species is polymorphic, differing in shell size, shape and number of spiral cords on the final two whorls. When found in shallow waters, the species tends to have thicker and more darkly pigmented shells with fewer spiral cords, while deep water specimens have thinner and lighter-coloured or white shells with more heavily nodular spiral cords. Transitional forms of shells exist where deep water and shallow water populations overlap or border.
It can be differentiated from M. osbornei due to having a less acute spire, finer sculpture, and by M. osbornei having obsolescent interstitial threads. It can be differentiated from M. punctulata due to having more robuse axial ribs.
The species was first described by A. W. B. Powell in 1931, using the name Maurea (Mucrinops) granti. He named the species after Whanganui museum director and conchologist Maxwell James Grant Smart. The holotype was collected in January 1931 by Powell near the mouth of the Waihi Stream near HÃÂwera, South Taranaki. It is held in the collections of Auckland War Memorial Museum. When describing the species in 1931, Powell believed it was a fossil species ancestral to M. osbornei.
In 2016, Maurea was raised to genus level, leading to the species' accepted name in the World Register of Marine Species to become Maurea granti. The New Zealand Organisms Register lists the species' preferred name as Calliostoma granti, and the New Zealand Inventory of Biodiversity (2009) lists the species' preferred name as Calliostoma (Maurea) granti.
M. granti primarily feeds on Cnidaria. It is a known host for the slipper snail species Maoricrypta youngi.
The species is endemic to New Zealand, found offshore the North Island south of East Cape and Cape Egmont, South Island, Stewart Island, Auckland Islands, Campbell Islands and Chatham Islands at a depth ranging between . Fossils of the species date back to the Waipipian stage of the Pliocene (3.7 million years ago) in New Zealand.