''Cantharidus opalus'', common name the opal top shell or in the

Māori language Māori (), or ('the Māori language'), also known as ('the language'), is an Eastern Polynesian language spoken by the Māori people, the indigenous population of mainland New Zealand. Closely related to Cook Islands Māori, Tuamotuan, and ...

matangongore, is a species of large

sea snail Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the ...

, a

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

gastropod The gastropods (), commonly known as snails and slugs, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, from freshwater, and from land. T ...

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

in the family Trochidae, 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 The body whorl is part of the morphology of the shell in those gastropod mollusks that possess a coiled shell. The term is also sometimes used in a similar way to describe the shell of a cephalopod mollusk. In gastropods In gastropods, the b ...

and yellowish or pinkish on the spire, 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 A protoconch (meaning first or earliest or original shell) is an embryonic or larval shell which occurs in some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod. In older texts it is also called ...

is conical, small, acute, and consists of 2½ convex smooth and pinkish-brown whorls. The shell contains 8 to 10

whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...

s. The first very slowly, then rapidly increase. The whorls are straight or slightly convex. The

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 is ovate-rhoniboidal. It is lined with iridescent green nacre with red reflections. The outer lip is thin, and slightly sulcate within. There is often a broad opaque white callosity following a greenish edge inside. The columella 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, 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