''Cantharidus opalus'', common name the opal top shell or in the Māori language matangongore, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of large sea snail, a marine gastropod mollusc in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Trochidae The Trochidae, common name top-snails or top-shells, are a family of various sized sea snails, marine gastropod molluscs in the subclass Vetigastropoda. This family is commonly known as the top-snails because in many species the shell resemb ...

, the top snails.Rosenberg, G. (2012). Cantharidus opalus (Martyn, 1784). Accessed through: World Register of Marine Species at http://www.marinespecies.org/aphia.php?p=taxdetails&id=590656 on 2012-11-27

Description

The length of the shell varies between 23 mm and 45 mm. The large, imperforate shell has an elevated conical shape. It is angular at the periphery, solid, but not very thick. Its spiral sculpture, not conspicuous, subobsolete. It is obsoletely distantly spirally grooved. These number about 7 on the penultimate whorl, mostly indistinct, crossed by more or less distinct oblique growth lines . The base of the shell contains about 5 spiral separated narrow ridges, often inconspicuous. The colour is whitish, tinged with blue on the body whorl and yellowish or pinkish on the

spire A spire is a tall, slender, pointed structure on top of a roof of a building or tower, especially at the summit of church steeples. A spire may have a square, circular, or polygonal plan, with a roughly conical or pyramidal shape. Spires a ...

, all over closely longitudinally marked with longitudinal zigzag markings of purple. These markings are often interrupted into spiral series of articulations. The epidermis is thin, shining, and easily rubbed off. The spire is elevated conic. Its sides are straight or slightly concave, more or less eroded, and showing the iridescent green nacre at the tip. The protoconch is conical, small, acute, and consists of 2½ convex smooth and pinkish-brown whorls. The shell contains 8 to 10 whorls. The first very slowly, then rapidly increase. The whorls are straight or slightly convex. The body whorl is distinctly angled at the periphery. The base of the shell is flatly convex. The sutures are well impressed, sometimes subcanaliculate on the lower whorls. The oblique

aperture In optics, an aperture is a hole or an opening through which light travels. More specifically, the aperture and focal length of an optical system determine the cone angle of a bundle of rays that come to a focus in the image plane. An ...

is ovate-rhoniboidal. It is lined with iridescent green nacre with red reflections. The outer

lip The lips are the visible body part at the mouth of many animals, including humans. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech. Human lips are a tactile sensory organ, and can be ...

is thin, and slightly sulcate within. There is often a broad opaque white callosity following a greenish edge inside. The

columella Lucius Junius Moderatus Columella (; Arabic: , 4 – ) was a prominent writer on agriculture in the Roman Empire. His ' in twelve volumes has been completely preserved and forms an important source on Roman agriculture, together with the wo ...

is subvertical, 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.

Distribution

This marine species is endemic to

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

, where it is found subtidally in kelp beds down to at least 15m, on semi-exposed to exposed coasts.Cook, Steve De C., “New Zealand Coastal Marine Invertebrates Vol 1”, Canterbury University Press, NZ 2010, ISBN 978-1877257-60-5

References

* Powell A. W. B., ''New Zealand Mollusca'', William Collins Publishers Ltd, Auckland, New Zealand 1979 * Marshall B.A. 1998. ''The New Zealand Recent species of Cantharidus Montfort, 1810 and Micrelenchus Finlay, 1926 (Mollusca: Gastropoda: Trochidae).'' Molluscan Research 19(1): 107-156

External links

* {{Taxonbar, from=Q5033764 opalus Gastropods of New Zealand Gastropods described in 1784