Mitra ustulata on Guam

by Paul Merril

Mitra ustulata Reeve, 1844. Two different forms of this miter are found hereon Guam. The species is highly variable in form and sculpture. Figure 5 is the typical form. This shell is generally smaller, smoother, and narrower than the other form. The two forms may represent sexual differences in the species.

Mitra ustulata form ignobilis Reeve, 1844. The following is Reeve's original description:

The Ignoble miter, this shell is rather stout, slightly recurved at the base, spire acuminated, transversely grooved throughout, grooves close-set, rather superficial; whitish, clouded with rows of large burnt brown spots; columella six-plaited, lowest plaits somewhat obscure. HABITAT: Island of Ticao, Philippines (found on the reef at low water); Cuming.

This shell is one of the larger shells of the family Mitridae. It may reach a length of about 75mm and is seldom found with a good protoconch. This shell is very elusive here on Guam and may be considered a moderately rare find. To my knowledge, there have been only 10 specimens of the Ignoble miter found on Guam. Its habitat appears to be deep within boulders with silty sand around them. This miter seems to be restricted to one locality on Guam. I first stumbled onto this shell while diving along the Glass Breakwater at about 30 feet, in June 1978. It was about a month later when I found out the name of this shell. Richard Salisbury identified it, and said that I had found the first Mitra ustulata form ignobilis to be recorded from Guam. Since that time, I have found about 8, and two other divers have brought up 1 each.