Pyrgulina alveata
Encyclopedia
Pyrgulina alveata is a species
of very small sea snail
, a pyramidellid
gastropod micromollusk
. This genus is currently placed in the subfamily Chrysallidinae
of the family
Pyramidellidae
.
are decollated. The five post-nuclear whorls are rather high between the sutures, moderately rounded, strongly shouldered at the summit, which is subtabulated. They are crossed by strong, rounded, almost vertical axial ribs, which render the summit of the whorls crenulate. Eighteen of these ribs occur upon the third, and nineteen upon the penultimate whorl. The intercostal spaces are about one-half as wide as the ribs, crossed by about twelve fine, subequally spaced, incised spiral lines. The summits of succeeding whorls fall a little anterior to the somewhat angulated periphery of the preceding whorl on the earlier volutions, and gives them a somewhat constricted appearance at the deep sutures. The periphery of the body whorl
is very faintly angulated. The base of the shell is well rounded, somewhat pinched at the umbilical region. It is marked by the strong continuations of the axial ribs, and about ten spirally incised lines in the spaces between them. The aperture
is oval. The posterior angle is obtuse. The outer lip
is thick showing seven equally well-developed and equally spaced internal lirations. The columella is short, decidedly curved and revolute, with a strong oblique fold at its insertion. The parietal wall is covered by a thin callus.
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 very small sea snail
Snail
Snail is a common name applied to most of the members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in its most general sense, it includes sea snails, land snails and freshwater snails. The word snail without any qualifier is however more often...
, a pyramidellid
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....
gastropod micromollusk
Micromollusk
A micromollusk is a descriptive term for a shelled mollusk which is extremely small, even at full adult size. The word is usually, but not exclusively, applied to marine mollusks, although in addition, numerous species of land snails and freshwater mollusks also reach adult size at very small...
. This genus is currently placed in the subfamily Chrysallidinae
Chrysallidinae
Chrysallidinae is a taxonomic group of very small sea snails in the family Pyramidellidae.- Taxonomy :Chrysallidinae has been one of eleven recognized subfamilies of the gastropod family Pyramidellidae...
of 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....
.
Description
The small shell measures 2 mm. It is oblong, ovate, milk-white. The 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 decollated. The five post-nuclear whorls are rather high between the sutures, moderately rounded, strongly shouldered at the summit, which is subtabulated. They are crossed by strong, rounded, almost vertical axial ribs, which render the summit of the whorls crenulate. Eighteen of these ribs occur upon the third, and nineteen upon the penultimate whorl. The intercostal spaces are about one-half as wide as the ribs, crossed by about twelve fine, subequally spaced, incised spiral lines. The summits of succeeding whorls fall a little anterior to the somewhat angulated periphery of the preceding whorl on the earlier volutions, and gives them a somewhat constricted appearance at the deep sutures. 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 faintly angulated. The base of the shell is well rounded, somewhat pinched at the umbilical region. It is marked by the strong continuations of the axial ribs, and about ten spirally incised lines in the spaces between them. 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 oval. The posterior angle is obtuse. 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....
is thick showing seven equally well-developed and equally spaced internal lirations. The columella is short, decidedly curved and revolute, with a strong oblique fold at its insertion. The parietal wall is covered by a thin callus.