About Cantharidus opalus (Martyn, 1784)
Cantharidus opalus (Martyn, 1784) is a marine species of sea snail. The shell of this species ranges in length between 23 mm and 45 mm. It is large, imperforate, solid but not very thick, and has an elevated conical shape, with an angular periphery. The spiral sculpture of the shell is not conspicuous and is subobsolete; the shell is marked with obsolete, widely spaced spiral grooves. There are around 7 of these grooves on the penultimate whorl, and they are mostly indistinct. They are crossed by more or less distinct oblique growth lines. The base of the shell has around 5 separate narrow spiral ridges, which are often inconspicuous. The base color of the shell is whitish, with a blue tinge on the body whorl and a yellowish or pinkish tinge on the spire. The entire shell is covered in close, longitudinal purple zigzag markings. These markings are often interrupted to form spiral series of articulations. The epidermis is thin, shining, and easily rubbed off. The spire is elevated conical, with straight or slightly concave sides. It is more or less eroded, and shows iridescent green nacre at the tip. The protoconch is small, acute, and conical, and is made up of 2ยฝ convex, smooth, pinkish-brown whorls. The full shell contains 8 to 10 whorls, which increase in size very slowly at first, then rapidly. The whorls are straight or slightly convex. The body whorl is distinctly angled at the periphery, and the base of the shell is flatly convex. The sutures are well impressed, and are sometimes subcanaliculate on the lower whorls. The oblique aperture is ovate-rhomboidal. It is lined with iridescent green nacre that has red reflections. The outer lip is thin, and slightly sulcate inside. It often has a broad opaque white callosity that follows a greenish edge on the inside. The columella is subvertical, and is generally straight in the middle or slightly projecting. The inner lip spreads as a broad white callus a little beyond the columella and over the parietal wall. This marine species is endemic to New Zealand. It can be found subtidally in kelp beds down to at least 15m depth, on semi-exposed to exposed coasts.
