''Gibbula beckeri'' 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), ...

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 ...

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

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.

Description

The size of the shell attains . The shell consists of 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 " ...

nucleus plus 4

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. The profile is rather strongly convex in the upper half of the whorl. There are spiral lirae 2 on 2nd and 3rd whorls, 3 on 4th whorl. These are broad and low, scarcely projecting above the profile, defined by impressed striae, the 3rd being peripheral and feebly carinate; an additional stria (or 2) between 1st and 2nd lirae, and 2-3 between 2nd and 3rd. Sometimes (as in a cotype) only 1 (midwhorl) lira on 2nd and 3rd whorls, but the peripheral one comes into view on 4th whorl. On the base of the shell there is usually a marginal lira and 7-8 weaker lirae, variable. The

umbilicus Umbilicus may refer to: *The navel or belly button *Umbilicus (mollusc), a feature of gastropod, Nautilus and Ammonite shell anatomy *Umbilicus (plant), ''Umbilicus'' (plant), a genus of over ninety species of perennial flowering plants *Umbilicus ...

is not completely closed in the largest shells. The growth lines are distinct. The colour of the shell is grey or violaceous-grey with white or pale spots, radiating streaks, and/or zigzag marks. Very young shells (up to diameter) are uniformly violaceous. One specimen is yellowish with darker brown radiating patches forming a band below the suture, similar dark patches on the peripheral lira, between these two bands brown zigzags. Two specimens have red-brown radiating streaks on an emerald-green ground colour on 3rd and 4th whorls, streaks extending on to peripheral lira (cf. capensis). The base of the shell contains grey lirae, or is faintly streaked and spotted.Barnard K.H., Contributions to the knowledge of South African marine Mollusca; Annals of The South African Museum vol. 47; 1963
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Distribution

This species occurs in the Atlantic Ocean from

Namibia Namibia, officially the Republic of Namibia, is a country on the west coast of Southern Africa. Its borders include the Atlantic Ocean to the west, Angola and Zambia to the north, Botswana to the east and South Africa to the south; in the no ...

Port Alfred Port Alfred is a small town with a population of just under 26,000 in the Eastern Cape province of South Africa. It is situated on the eastern seaboard of the country at the mouth of the Kowie River, almost exactly halfway between the larger ci ...

, South Africa

References

* Kilburn, R.N. & Rippey, E. (1982) ''Sea Shells of Southern Africa''. Macmillan South Africa, Johannesburg, xi + 249 pp. page(s): 40 {{DEFAULTSORT:Gibbula Beckeri beckeri Gastropods described in 1901