Selenizone

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Four view of the slit shell Mikadotrochus hirasei. The first view shows the selenizone well. The other views show its relationship to the slit in the shell. Mikadotrochus hirasei 01.jpg
Four view of the slit shell Mikadotrochus hirasei . The first view shows the selenizone well. The other views show its relationship to the slit in the shell.
Three artificially polished shells of a New Zealand abalone, a Haliotis species, probably H. iris. The central shell clearly shows the selenizone as a series of holes Paua3.jpg
Three artificially polished shells of a New Zealand abalone, a Haliotis species, probably H. iris . The central shell clearly shows the selenizone as a series of holes

A selenizone (from the Greek "selene" meaning "moon", and "zone" meaning "girdle") is an anatomical structure that exists in the shells of some families of living sea snails: the slit shells, the little slit shells and the abalones, which are marine gastropod mollusks from ancient lineages.

Contents

It is a spiral band of crescentric growth lines or threads (lunulae) on the shell surface due to the semicircular end of a notch or slit on the outer lip. [1]

A structure of the same type exists in several fossil groups of mollusks, including all the fossil families of slit shells, as well as three superfamilies of what may have been gastropods, but may possibly have been monoplacophorans or paragastropods instead.

The function of the holes and slits in living sea snails is to allow for exhalant water circulation, which is important for respiration and other functions. It has also been suggested that the selenizone may serve to reinforce the shell against catastrophic breakage during predation attempts. [2]

A new shell-morphological term 'sutsel' has been introduced by Dr. Geiger for the area between the SUTure and the SELenizone. [3]

In living gastropods

In the Pleurotomariidae (the slit shells), and the Scissurellidae (the little slit shells), the selenizone is a groove on the periphery of the shell which forms as the shell grows by the gradual sealing up of a slit that extends back from the edge of the aperture of the shell.

In the Haliotidae, the abalones, the selenizone takes the form of a series of holes in the shell (reaching back from the leading growth edge of the aperture) which form as the shell grows. The older holes are gradually sealed up as the shell grows and new holes form. Each abalone species has a typical number of holes in the selenizone which remain open, and this feature is diagnostic for the individual species.

In fossil groups

A selenizone is also present in several superfamilies of fossil mollusks. Not surprisingly it is seen in the numerous fossil gastropod families within the Pleurotomarioidae. The selenizone also exists in the Bellerophontoidea, which may be gastropods or monoplacophorans; in the Euomphaloidea, which are probably gastropods, but may be monoplacophorans; and in the Macluritoidea, which are either archaeogastropods or Paragastropoda Linsley & Kier, 1984, (paragastropods are a group of mollusks that superficially resemble gastropods, but were untorted). [4]

Taxa

A list of superfamilies and families (both living and fossil) which show this structure, based on the taxonomy of Bouchet et al 2005. [5] The taxa that are entirely extinct are marked with a dagger † :

Extant taxa:

Fossil taxa:

Gastropods

Gastropods or monoplacophorans or paragastropods

Related Research Articles

Bellerophontidae Extinct family of gastropods

The Bellerophontidae are an extinct family of specialized globose bellerophontids, Paleozoic and early Triassic mollusks of the class Gastropoda.

Anatomidae is a family of minute sea snails, marine gastropod mollusks in the clade Vetigastropoda.

Pleurotomariacea Superfamily of molluscs

Pleurotomariacea is one of two names that are used for a taxonomic superfamily of sea snails that are an ancient lineage and are well represented in the fossil record. The name Pleurotomariacea is used by paleontologists, who, because they usually have only the hard parts of mollusks to study, often use a slightly different scheme of classification from that used by scientists who study living mollusks.

Vetigastropoda Clade of sea snails

Vetigastropoda is a major taxonomic group of sea snails, marine gastropod mollusks that form a very ancient lineage. Taxonomically the Vetigastropoda are sometimes treated as an order, although they are treated as an unranked clade in Bouchet and Rocroi, 2005.

The †Raphistomatidae is a taxonomic family of fossil sea snails, Paleozoic marine gastropod mollusks. This family was established by Koken in 1896. This family is found in the fossil record from the Upper Cambrian to the Middle Permian.

Sutilizona pterodon is a species of sea snail, a marine gastropod mollusk in the family Sutilizonidae.

<i>Anatoma umbilicata</i> Species of gastropod

Anatoma umbilicata is a species of sea snail, a marine gastropod mollusk in the family Anatomidae.

Sinezona singeri is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Scissurellidae, the little slit shells.

<i>Anatoma breveprima</i> Species of gastropod

Anatoma breveprima is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Anatomidae.

<i>Anatoma hyposculpta</i> Species of gastropod

Anatoma hyposculpta is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Anatomidae.

Anatoma japonica is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Anatomidae.

Scissurella clathrata is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Scissurellidae, the little slit snails.

<i>Scissurella jucunda</i> Species of gastropod

Scissurella jucunda is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Scissurellidae, the little slit snails.

Scissurella mirifica is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Scissurellidae, the little slit snails.

<i>Scissurella redferni</i> Species of gastropod

Scissurella redferni is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Scissurellidae, the little slit snails.

<i>Scissurella reticulata</i> Species of gastropod

Scissurella reticulata is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Scissurellidae, the little slit snails.

Scissurella supraplicata is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Scissurellidae, the little slit snails.

Sukashitrochus atkinsoni is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Scissurellidae, the little slit snails.

Anatoma gunteri, common name Gunther's split shell, is a species of minute sea snail, a marine gastropod mollusk or micromollusk in the family Anatomidae.

<i>Haliotis</i> Genus of gastropods

Haliotis, common name abalone, is the only genus in the family Haliotidae.

References

  1. ↑ "selenizone". Academic Dictionaries and Encyclopedias.
  2. ↑ "Repaired injuries and shell form in some Palaeozoicpleurotomarioid gastropods" (PDF). www.app.pan.pl. 2005. Retrieved 2021-04-06.
  3. ↑ Geiger D.L. (2012) Monograph of the little slit shells. Volume 1. Introduction, Scissurellidae. pp. 1-728. Volume 2. Anatomidae, Larocheidae, Depressizonidae, Sutilizonidae, Temnocinclidae. pp. 729-1291. Santa Barbara Museum of Natural History Monographs Number 7.
  4. ↑ "Welcome palaeos.org - BlueHost.com". www.palaeos.org.
  5. ↑ Bouchet P. & Rocroi J.-P. (Ed.); Frýda J., Hausdorf B., Ponder W., Valdes A. & Warén A. 2005. Classification and nomenclator of gastropod families. Malacologia: International Journal of Malacology, 47(1-2). ConchBooks: Hackenheim, Germany. ISBN   3-925919-72-4. ISSN 0076-2997. 397 pp.
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