''Coelotrochus chathamensis'' is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of small

sea snail Sea snails are slow-moving marine (ocean), marine gastropod Mollusca, molluscs, usually with visible external shells, such as whelk or abalone. They share the Taxonomic classification, taxonomic class Gastropoda with slugs, which are distinguishe ...

, a marine

gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...

mollusc Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

in the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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 resembles ...

, the top snails or top shells.

Description

The length of the shell varies between eight mm and 10 mm. The small shell has a conical shape, the sides are straight or slightly convex.. The angle of 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. Spire ...

is 70°. The five, rarely six,

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). In nature File:Photograph and axial plane floral diagra ...

s are flat with an elevated upper edge, and, together with the base, spirally striated. The pointed

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 regularly conical, and consists of about two whorls. These are not marked off from the succeeding whorl. This one is, smooth, with two or three spiral red bands. The last two whorls increase rapidly in size. They are flat to slightly convex above, concave below before reaching the strong and prominent cingulum. The body whorl has a distinct peripheric keel. The

sculpture Sculpture is the branch of the visual arts that operates in three dimensions. Sculpture is the three-dimensional art work which is physically presented in the dimensions of height, width and depth. It is one of the plastic arts. Durable sc ...

consists of five to six low spiral threads, the lower and upper margins much elevated, especially the former. They are crossed by broad nodulous radiate ribs, which, however, do not extend over the lower half of the whorl. These ribs are often obsolete. The suture is superficial, with a nodulous border below. The false umbilicus is narrow and not very deep. The oblique

aperture In optics, the aperture of an optical system (including a system consisting of a single lens) is the hole or opening that primarily limits light propagated through the system. More specifically, the entrance pupil as the front side image o ...

is rhomboidal. The outer and basal

lip The lips are a horizontal pair of soft appendages attached to the jaws and are the most visible part of the mouth of many animals, including humans. Mammal lips are soft, movable and serve to facilitate the ingestion of food (e.g. sucklin ...

are a little convex, forming a sharp angle where they meet. The oblique

columella Lucius Junius Moderatus Columella (, Arabic: ) was a prominent Roman writer on agriculture in the Roman Empire. His in twelve volumes has been completely preserved and forms an important source on Roman agriculture and ancient Roman cuisin ...

is slightly concave. It has an almost imperceptible posterior fold, but the anterior portion is nearly smooth. The axial cavity is small and smooth. The color of the shell is white, buff with pink or oblique brownish purple stripes or spots. The flat base of the shell is white with interrupted pink, subequal spiral lines.Suter H. (1913-1915), Manual of New Zealand Mollusca; Wellington, N. Z. :J. Mackay, govt. printer,1913-1915
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Distribution

This marine species is endemic to

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

and occurs the

Chatham Islands The Chatham Islands ( ; Moriori language, Moriori: , 'Misty Sun'; ) are an archipelago in the Pacific Ocean about east of New Zealand's South Island, administered as part of New Zealand, and consisting of about 10 islands within an approxima ...

, Southern North Island,

Stewart Islands Sikaiana (formerly called the Stewart Islands) is a small atoll NE of Malaita in Solomon Islands in the south Pacific Ocean. It is almost in length and its lagoon, known as Te Moana, is totally enclosed by the coral reef. Its total land surfa ...

and the

Auckland Islands The Auckland Islands ( Māori: ''Motu Maha'' "Many islands" or ''Maungahuka'' "Snowy mountains") are an archipelago of New Zealand, lying south of the South Island. The main Auckland Island, occupying , is surrounded by smaller Adams Island ...

References

* Powell A. W. B., ''New Zealand Mollusca'', William Collins Publishers Ltd, Auckland, New Zealand 1979 * Marshall B.A. 1998. ''A review of the Recent Trochini of New Zealand (Mollusca: Gastropoda: Trochidae).'' Molluscan Research 19(1): 73-106 {{Taxonbar, from=Q3141152 chathamensis Gastropods of New Zealand Gastropods described in 1873