Vertigo milium, common name

Common name

A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...

 the blade vertigo, is a species

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 air-breathing land 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 terrestrial

Terrestrial animal

Terrestrial animals are animals that live predominantly or entirely on land , as compared with aquatic animals, which live predominantly or entirely in the water , or amphibians, which rely on a combination of aquatic and terrestrial habitats...

 pulmonate gastropod mollusk in the family Vertiginidae

Vertiginidae

Vertiginidae is a family of minute, air-breathing land snails, terrestrial pulmonate gastropod molluscs or micromollusks in the superfamily Pupilloidea.- Distribution :...

.

Shell description

The shell

Gastropod shell

The gastropod shell is a shell which is part of the body of a gastropod or snail, one kind of mollusc. The gastropod shell is an external skeleton or exoskeleton, which serves not only for muscle attachment, but also for protection from predators and from mechanical damage...

 is small, subcylindrical, smooth shining. Growth lines are very fine, a little oblique. Apex

Apex (mollusc)

Apex is an anatomical term for the tip of the mollusc shell of a gastropod, scaphopod, or cephalopod mollusc.-Gastropods:The word "apex" is most often used to mean the tip of the spire of the shell of a gastropod...

 is smooth. The color of the shell is dark chest-nut. The shell has 5 rounded whorls

Whorl (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...

, that are somewhat regularly increasing and decreasing to a bluntly rounded apex. Sutures are 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 obscurely semicircular, lateral and truncated above. The "circumference" of the aperture is "made up of two curves of different radius uniting in the peristome, where the junction causes an angle projecting inwards, the smaller curve comprising about one-fourth part and forming the superior portion of the peristome. The aperture has six teeth as follows: two sharp, projecting teeth of about equal size placed on the parietal wall and dividing that region into three nearly equal parts; one on the columella, large, massive, broad; a third placed on the outer lip above or at the junction of the two radii, long, curved, ridge-like, pointing directly between the two parietal teeth; a fourth on the base of the lip, small, conical, tubercular; and one large, entering, elevated, long lamina, which begins on the base of the lip and curves backward until it disappears behind the columella tooth (this is the "gular lamina" of Sterki). Peristome is white or brownish-white, reflected, the terminations separated, but joined by a prominent callus. The umbilicus is well marked, open, deep. Base of the shell is rounded.

The width of the shell is 0.80-0.90 mm. The height of the shell is 0.90-1.40 mm. The height of aperture is 0.25-0.30 mm.

Anatomy

The animal is similar in form to the other species of Vertigo. The color is dirty white, darker on the upper surface. The foot is very broad,
posterior of the center, from whence it tapers rapidly to a point. The the foot is thick and fleshy and well able to support the light shell. Eye-peduncles are of medium length, somewhat enlarged at the tips, where the eyes are placed.

The jaw is very slightly arcuate, the ends a trifle rounded. Concave margin is notched and anterior surface lightly striated. The jaw is of equal width throughout its length.

The formula of the radula

Radula

The radula is an anatomical structure that is used by molluscs for feeding, sometimes compared rather inaccurately to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus...

 is like this: ₂ ⁷ ₇ + + + + ₂ ⁷ ₇

Teeth are as in the other members of the genus. There are four perfect lateral teeth and the first marginal tooth is similar but with a second outer
cusp. From this point the marginals become wider, the inner cusp remains always the larger, and the outer cusp develops from five to seven small cusps or denticles.

Distribution

Distribution of Vertigo milium include Illinois

Illinois

Illinois is the fifth-most populous state of the United States of America, and is often noted for being a microcosm of the entire country. With Chicago in the northeast, small industrial cities and great agricultural productivity in central and northern Illinois, and natural resources like coal,...

, Maine

Maine

Maine is a state in the New England region of the northeastern United States, bordered by the Atlantic Ocean to the east and south, New Hampshire to the west, and the Canadian provinces of Quebec to the northwest and New Brunswick to the northeast. Maine is both the northernmost and easternmost...

 to Minnesota

Minnesota

Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...

, Ontario

Ontario

Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....

 and Quebec

Quebec

Quebec or is a province in east-central Canada. It is the only Canadian province with a predominantly French-speaking population and the only one whose sole official language is French at the provincial level....

, Canada, to Florida

Florida

Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...

 and Texas

Texas

Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

, USA.

Habitat

Baker (1902) described habitat like this: "Gregarious. Found plentifully under leaves, stones and sticks, in moist situations."

External links

• photos of live Vertigo milium
• photo of the shell of Vertigo milium
• photos of shells of Vertigo milium
• Manual of Conchology, volume 25, plate 13, figures 1-7.