Oscilla circinata
Encyclopedia
Oscilla circinata is a species
of sea snail
, a marine
gastropod mollusk in the family
Pyramidellidae
, the pyrams and their allies.
of the protoconch
are small, almost completely immersed in the first post-nuclear whorl, only the rounded two-thirds of the last volution are visible, and those indicate that the axis of the nuclear turns must be at a right angle to the axis of the later whorls. The five whorls of the teleoconch are moderately well rounded, the last one somewhat inflated, shouldered. They are marked by strong, broadly rounded, subequal and subequally spaced spiral keels. These are separated by deep, rounded sulci, which are about as wide as the keels. The sulci are crossed by extremely fine and very closely spaced axial raised threads which pass up on the sides of the spiral keels, but do not cross their summits. The second and third whorls have three keels between the sutures. On the third whorl the posterior keel at the summit of the whorl, which is a little wider than the other two, shows a spiral striation on its middle. This grows gradually stronger as the shell advances, until on the penultimate whorl it has divided this keel into two, the posterior one of which is a little less developed than the anterior one, which resembles the other between the sutures. The summit of the last whorl falls considerably below the periphery, showing five spiral keels between the sutures on the penultimate whorl. The periphery of the body whorl
is sulcate, sulcus like the rest and similarly sculptured. The base of ther shell is well rounded, somewhat attenuated anteriorly, sculptured like the spaces between the sutures, having seven spiral keels. These keels diminish somewhat in size from the periphery to the umbilical area. The aperture
is subovate. The posterior angle is acute. The outer lip
thin, wavy, showing the external sculpture
within. The columella is decidedly curved, re-enforced anteriorly by the attenuated base. It is provided with a very strong,acute, oblique fold near 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 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 elongate-oval shell is subdiaphanous. It measures 2.1 mm. The 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...
of the protoconch
Protoconch
A protoconch is an embryonic or larval shell of some classes of molluscs, e.g., the initial chamber of an ammonite or the larval shell of a gastropod...
are small, almost completely immersed in the first post-nuclear whorl, only the rounded two-thirds of the last volution are visible, and those indicate that the axis of the nuclear turns must be at a right angle to the axis of the later whorls. The five whorls of the teleoconch are moderately well rounded, the last one somewhat inflated, shouldered. They are marked by strong, broadly rounded, subequal and subequally spaced spiral keels. These are separated by deep, rounded sulci, which are about as wide as the keels. The sulci are crossed by extremely fine and very closely spaced axial raised threads which pass up on the sides of the spiral keels, but do not cross their summits. The second and third whorls have three keels between the sutures. On the third whorl the posterior keel at the summit of the whorl, which is a little wider than the other two, shows a spiral striation on its middle. This grows gradually stronger as the shell advances, until on the penultimate whorl it has divided this keel into two, the posterior one of which is a little less developed than the anterior one, which resembles the other between the sutures. The summit of the last whorl falls considerably below the periphery, showing five spiral keels between the sutures 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 sulcate, sulcus like the rest and similarly sculptured. The base of ther shell is well rounded, somewhat attenuated anteriorly, sculptured like the spaces between the sutures, having seven spiral keels. These keels diminish somewhat in size from the periphery to the umbilical area. 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 subovate. The posterior angle is acute. 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....
thin, wavy, 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 decidedly curved, re-enforced anteriorly by the attenuated base. It is provided with a very strong,acute, oblique fold near its insertion. The parietal wall is covered by a thin callus.