Odostomia excolpa
Encyclopedia
Odostomia excolpa is a species
of sea snail
, a marine
gastropod mollusk in the family
Pyramidellidae
, the pyrams and their allies.
are quite large, forming a moderately elevated, helicoid spire, whose axis is at right angles to that of the succeeding turns, in the first of which it is about one-fourth immersed. The five post-nuclear whorls are decidedly rounded, with the greatest convexity falling on the anterior third of the whorls, between the sutures, appressed at the summit. They are marked by decidedly sinuous, slender, axial ribs, of which about 18 occur upon the first and second, 20 upon the third, and 28 upon the penultimate turn. The intercostal spaces are about three times as wide as the ribs. In addition to the axial sculpture
, the whorls are crossed by three equal and subequally spaced, spiral threads, which are almost as strong as the axial ribs. The first of these is situated at the posterior termination of the anterior third, between the sutures,while the third marks the periphery, the second being halfway between the two. The intersections of the spiral threads and axial ribs are lightly nodulose, while the spaces enclosed between them appear as almost square pits. The base of the shell is well rounded, marked by four slender, spiral threads and the feeble continuations of the axial ribs, which extend to the umbilical area. The sutures are strongly impressed.The aperture
is ear-shaped. The posterior angle is acute. The outer lip
is thin, showing the external sculpture within. The inner lip is slightly curved, decidedly revolute, adnate to the base, provided with a strong, obliquo fold at its insertion. The parietal wall is covered with a thick callus, which connects the insertion of the inner lip with the posterior angle of the aperture.
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 shell is very small, measuring 2 mm. It is semitranslucent, bluish-white. The 2 ½ 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 quite large, forming a moderately elevated, helicoid spire, whose axis is at right angles to that of the succeeding turns, in the first of which it is about one-fourth immersed. The five post-nuclear whorls are decidedly rounded, with the greatest convexity falling on the anterior third of the whorls, between the sutures, appressed at the summit. They are marked by decidedly sinuous, slender, axial ribs, of which about 18 occur upon the first and second, 20 upon the third, and 28 upon the penultimate turn. The intercostal spaces are about three times as wide as the ribs. In addition to the axial 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...
, the whorls are crossed by three equal and subequally spaced, spiral threads, which are almost as strong as the axial ribs. The first of these is situated at the posterior termination of the anterior third, between the sutures,while the third marks the periphery, the second being halfway between the two. The intersections of the spiral threads and axial ribs are lightly nodulose, while the spaces enclosed between them appear as almost square pits. The base of the shell is well rounded, marked by four slender, spiral threads and the feeble continuations of the axial ribs, which extend to the umbilical area. The sutures are strongly impressed.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 ear-shaped. 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....
is thin, showing the external sculpture within. The inner lip is slightly curved, decidedly revolute, adnate to the base, provided with a strong, obliquo fold at its insertion. The parietal wall is covered with a thick callus, which connects the insertion of the inner lip with the posterior angle of the aperture.