Both groups fall under the division Euthyneura, while the majority of the marine univalves belong to the division Streptoneura (i.
The juvenile shell-collector usually begins his knowledge of the classification of the Mollusca, by learning that shells are classified as Univalves and Bivalves.
A few univalves also occurred, but they were so extremely imperfect that their genera could not be made out.
While the oyster deposits vast quantities of eggs, which float out into the water to be destroyed by other animals, many of the univalves protect their eggs in remarkable cases.
Many of the univalves are flesh eaters, preying upon others of their kind.
In the first place, though it has pedicels similar to those on which the eyes of the higher univalves are placed, yet it has no eyes.
The reader will have observed that the periwinkle, whelk, and other univalves close their shells by a kind of lid when they retract their bodies.
A few of the univalves are viviparous--that is, they produce their young alive; but the majority lay eggs.
The univalves have now simply to be placed mouth downwards on blotting-paper to drain and dry, when they are ready for the cabinet.
Many of the univalves here at San Lorenzo were filled with, and united together by, pure salt, probably left by the evaporation of the sea-spray, as the land slowly emerged.
The carbonate of lime is obviously derived from the shells; and common salt is so abundant in parts of the bed, that, as before remarked, the univalves are often filled with it.
Among the univalves I can distinguish Dentalium entale, Purpura lapillus, Turritella terebra, and Littorina littorea, all existing shells, but all common also to at least the later deposits of the Crag.
Baltica) and a few minuteunivalves allied to Paludina ulva.
Among many univalves agreeing with those of Africa on the eastern side of the Atlantic are Cypraea sanguinolenta, Buccinum lyratum, and Oliva flammulata.
In some also of the spiral univalves the pattern of the original painting is distinctly retained, as in Pleurotomaria (Figure 486), which displays wavy blotches, resembling the colouring in many recent trochidae.
The operculum, or lid, in univalves is that part which fits exactly into the aperture, and incloses the animal; it serves as a door to the shell.
I think that it will be best to pause a little before we enter upon the study of the twelfth class, Mollusca, which contains most of the univalves of Linnæus.
Tell me what genera remain to be noticed among the univalves of Linnæus?
Note: Most univalves are spiral and are the shells of gastropods, but many belong to cephalopods and pteropods.
A large number of univalves belonging to the gastropods are conical, cup-shaped, or shieldlike, as the limpets.
Notwithstanding, therefore, the peculiarity of the chambered univalves of various genera, so abundant in the chalk, the Mollusca of the period approximate in character to the tertiary and recent Fauna far more than was formerly supposed.
Out of one hundred and forty-two species of univalves obtained from the Minchinhampton beds, Mr. Lycett found no less than forty-one to be carnivorous.
Several spiralunivalves are abundant, among which are many species of Pleurotomaria and Euomphalus.
Amongst the Jurassic Univalves (Gasteropoda) there are many examples of the ancient and long-lived Pleurotomaria; but on the whole the Univalves begin to have a modern aspect.
The Univalves (Gasteropoda) are very numerous, and a few characteristic forms are here figured (fig.
The curious oceanic Univalves known as the Heteropods are also very abundant, the principal forms belonging to Bellerophon and Maclurea.
Not only is this the case, but a large number of the Eocene Univalves belong to types which now attain their maximum of development in the warmer regions of the globe.
Thus the marine beds of the Lignitic series contain such characteristic Cretaceous forms as Inoceramus and Ammonites, along with a great number of Univalves of a distinctly Tertiary type (Cones, Cowries, &c.
The Univalves (Gasteropods) of the Cretaceous period are not very numerous, nor particularly remarkable.
The more strictly fresh-water deposits of the Eocene period have also yielded numerous remains of Univalves such as are now proper to rivers and lakes, together with the shells of true Land-snails.
The Univalves (Gasteropoda) are also very numerous, the two most important genera being Murchisonia (fig.
Most univalves are spiral and are the shells of gastropods, but many belong to cephalopods and pteropods.
Submerged sandbars are good spots to find several kinds of univalves and bivalves, but the latter will dig themselves quickly out of sight--as far down as several feet.
Univalves have only one shell, usually coiled, but sometimes shaped like a cap or miniature volcano.
Your univalves will be more difficult; remove the animal with a crocket hook or other piece of bent wire, turning it gently with the spiral; try to get it out whole to save yourself trouble.
Univalves are conical and spiraling, with a series of whorls coming down like widening steps from the tiny nucleus on top.
Some marine univalves can seal themselves inside with an operculum, which covers the open end of the shell like a trap door.
The first two include Univalves and Bivalves, the last only Univalves.
The former are univalvesand the latter bivalves having two shells for protection.
From the character of the shells of marine univalves inclosed in this tuff, it appears to have been formed in shallow water.
Univalves not possessed of a siphon may generally be considered herbivorous; they pass most of their time peacefully browsing upon algae.
The univalves which possess a siphon are, for the most part, carnivorous, and are often most voracious creatures.
The whorls of spiral univalves generally take an oblique direction in reference to the imaginary axis of the shell.
Many other terms are used to express difference in Bivalves, but being generally applicable to Univalves and Multivalves, as well as to them, they will be found explained at large in the alphabetical part of the work.
The greater part of univalvesare non-symmetrical, being rolled obliquely on the axis; but many are symmetrical, being rolled horizontally on the axis.
The next variation in symmetrical univalves is to be observed in the tubular, curved form, the example of which will be the Dentalium, fig.
A term of distinction applied by De Blainville, to those spiral univalves which have an operculum; these, as they constitute two distinct pieces, he considers as forming a medium between univalves and bivalves.
Beads made from the columellae of univalveshave generally a number of distinguishing characteristics.
A considerable number of the larger species of marine univalveshave been brought into requisition.
The consideration of these pins leads naturally to the presentation of other classes of objects manufactured from the columellae of marine univalves among which beads are the most numerous and important.
Our collections furnish no examples of marine univalves worked in this manner; a few slightly altered specimens, however, have been reported.
The whole of the univalves and bivalves received from Messrs.
We believed the univalves had been chiefly described by him; one, or probably two of the species were not contained in his memoir.
Yet, since each of these three univalves has been this day created, these inferences are deceptive.
Now, the increase of the shell in the Univalves is performed almost exactly as in the Bivalves; namely, by the protrusion and eversion of the mantle on the existing edge.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "univalves" in a variety of sentences. We hope that you will now be able to make sentences using this word.
