Odostomia amanda
Encyclopedia
Odostomia amanda is a species
of sea snail
, a marine
gastropod mollusk in the family
Pyramidellidae
, the pyrams and their allies.
are moderately large, helicoid. They have their axis at a right angle to the axis of the later whorls and are scarcely immersed in the first of them. The seven post-nuclear whorls are moderately rounded, somewhat shouldered. They are ornamented by strong rounded vertical or slightly backward-slanting axial ribs which are thickened at the summit to form small cusps. Sixteen of these ribs occur upon the first, twenty upon the third, twenty-two upon the fifth, and twenty-six upon the penultimate whorl. The intercostal spaces are about as wide as the ribs, crossed by well-incised, equal and subequally spaced spiral lines which are about one-fourth as wide as the spaces enclosed between them. There are no spiral
lines in the intercostal spaces near the summit of the whorls; the first one falls about parallel with the anterior limit of the cuspid summit of the axial ribs; nine lines occur between the sutures on the fourth, eleven on the fifth, and twelve on the penultimate whorl. The periphery of the body whorl
is very slightly angulated.The base of the shell is well rounded. It is marked by strong continuations of the axial ribs, which extend to the umbilical region, and eighteen incised spiral lines in the intercostal spaces. These lines gradually become more crowded toward the umbilical region. The aperture
is moderately large, suboval, somewhat effuse at the junction of the outer lip
and columella. The posterior angle is acute.The outer lip is thin, showing the external sculpture
within. The columella is oblique, slightly curved, and somewhat revolute, re-enforced by the somewhat attenuated basal portion of the body whorl. It is provided with a weak oblique fold at its insertion. The parietal wall has no perceptible callus.
, Fiji, and also off Upulu Island, Samoa
.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of sea snail
Sea snail
Sea snail is a common name for those snails that normally live in saltwater, marine gastropod molluscs....
, a marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...
gastropod mollusk in the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Pyramidellidae
Pyramidellidae
Pyramidellidae, common name the pyram family, or pyramid shells, is a voluminous taxonomic family of mostly small and minute ectoparasitic sea snails, marine heterobranch gastropod molluscs or micromolluscs....
, the pyrams and their allies.
Description
The slender shell is elongate, conic, milk-white. It measures 3 mm. The three nuclear whorlsWhorl (mollusc)
A whorl is a single, complete 360° revolution or turn in the spiral growth of a mollusc shell. A spiral configuration of the shell is found in of numerous gastropods, but it is also found in shelled cephalopods including Nautilus, Spirula and the large extinct subclass of cephalopods known as the...
are moderately large, helicoid. They have their axis at a right angle to the axis of the later whorls and are scarcely immersed in the first of them. The seven post-nuclear whorls are moderately rounded, somewhat shouldered. They are ornamented by strong rounded vertical or slightly backward-slanting axial ribs which are thickened at the summit to form small cusps. Sixteen of these ribs occur upon the first, twenty upon the third, twenty-two upon the fifth, and twenty-six upon the penultimate whorl. The intercostal spaces are about as wide as the ribs, crossed by well-incised, equal and subequally spaced spiral lines which are about one-fourth as wide as the spaces enclosed between them. There are no spiral
Spire (mollusc)
A spire is a descriptive term for part of the coiled shell of mollusks. The word is a convenient aid in describing shells, but it does not refer to a very precise part of shell anatomy: the spire consists of all of the whorls except for the body whorl...
lines in the intercostal spaces near the summit of the whorls; the first one falls about parallel with the anterior limit of the cuspid summit of the axial ribs; nine lines occur between the sutures on the fourth, eleven on the fifth, and twelve on the penultimate whorl. The periphery of the body whorl
Body whorl
Body whorl is part of the morphology of a coiled gastropod mollusk.- In gastropods :In gastropods, the body whorl, or last whorl, is the most recently-formed and largest whorl of a spiral or helical shell, terminating in the aperture...
is very slightly angulated.The base of the shell is well rounded. It is marked by strong continuations of the axial ribs, which extend to the umbilical region, and eighteen incised spiral lines in the intercostal spaces. These lines gradually become more crowded toward the umbilical region. The aperture
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
is moderately large, suboval, somewhat effuse at the junction of the outer lip
Lip (gastropod)
In the shell of a gastropod mollusk , the margin of the aperture is called the lip or the peristome. In other words, this is a term used to describe part of gastropod shell anatomy....
and columella. The posterior angle is acute.The outer lip is thin, showing the external sculpture
Sculpture (mollusc)
The sculpture of a mollusc shell is the three-dimensional ornamentation on the outer surface, as distinct from the basic shape of the shell itself or colouration. Sculpture may be concave as well as convex. Sometimes it has microscopic detail. Sculpture refers to the calcareous outer layer, not the...
within. The columella is oblique, slightly curved, and somewhat revolute, re-enforced by the somewhat attenuated basal portion of the body whorl. It is provided with a weak oblique fold at its insertion. The parietal wall has no perceptible callus.
Distribution
This species occurs in the Pacific Ocean off Viti Levu GroupViti Levu Group
The Viti Levu Group in Fiji consists of the island of Viti Levu and its outliers, including Bau, Beqa, Nukulau, and Vatulele. The group had an aggregate area of 10,453 square kilometers and a population of 574,801 at the 1996 census....
, Fiji, and also off Upulu Island, Samoa
Samoa
Samoa , officially the Independent State of Samoa, formerly known as Western Samoa is a country encompassing the western part of the Samoan Islands in the South Pacific Ocean. It became independent from New Zealand in 1962. The two main islands of Samoa are Upolu and one of the biggest islands in...
.