In this family we reach a group of Gasteropods much more numerous, both in species and in special types, which respire by the aid of branchiæ, or gills.
In the Pectinibranchial Gasteropods the gills are composed of numerous leaflets cut like the teeth of a comb, and attached, on one or many lines, to the upper part of the respiratory cavity.
Magnificent examples may be seen in the church of Saint Sulpice, Paris, where they hold the holy water.
These Molluscs belong to the seas of warm countries, where they frequent the sandy bottoms and clear waters.
Cyclostoma is perhaps the best known; the mouth is circular, the name being derived from cyclos, circle, and stoma, mouth.
The genus Fusus, or spindle shells, is distinguished by the elegance of its form rather than by the brilliancy of its colours.
The mass consists of a great number of small bladders, which combine to keep the animal on the surface of the water.
One notable genus of marine gasteropods possesses both lungs and gills, and one marine form has entirely lost its gills and breathes only by means of lungs.
It is fairly safe to assume that all gasteropods that possess a proboscis are carnivorous.
The radula has been the subject of much study by conchologists, and has furnished the basis for an arrangement of the numerous sections of gasteropods into somewhat well-defined groups.
In other respects the presence of certain specialized organs would probably indicate that gasteropods belonging to this suborder are a step higher in the scale of life than those which belong to the /Diatocardia/.
The majority of the gasteropods are lethargic and slow in movement, but others will be found to be exceedingly lively and able to creep up the sides of the jar and make their escape in a surprisingly short time.
This theory may not be satisfactory, but the asymmetry of gasteropods is a problem to be solved, and a more interesting line of biological investigation could not be found.
There are, however, some rather peculiar developments in the breathing system of gasteropods that are worthy of notice.
There is evidence tending to show that in past geological epochs the pelecypods (the bivalve shells) outnumbered the gasteropods, but that in the course of time the increase in the genera of gasteropods has been more [pg349] rapid.
Of the air-breathing aquatic and (10) terrestrial gasteropods the most interesting particulars are their generative organs, which the author proposes to re-examine.
The symmetrical shell of the lower Gasteropods undergoes a lateral torsion in the higher, spiral forms, to become again symmetrical in the Cephalopoda.
Gasteropods were well represented and included many modern genera.
These must be sought at the bottom; but on the weeds, or on the bottom, will be found not a few species of gasteropods or univalves, some of which we may have noticed in a freshwater aquarium.
Most gasteropodswhich live in water have this; most which live on land (only two exceptions in British molluscs) have not.
Next above the Gasteropods comes a group of animals forming the class Pteropoda.
There are a few Gasteropods in which the shell consists of a series of similar segments as is the case with Chiton, while many are altogether naked.
An eye is present in most Gasteropods and in many larval Pteropods.
Up to this time the embryo has been symmetrical, but in most Gasteropods the shell and mantle extend very much more towards the left than towards the right side, and a commencement of the permanent spiral shell is thus produced.
This cavity is as inGasteropods open to the yolk-sack, and only separated from the yolk itself by the yolk membrane already spoken of.
The condition of the eye, with a closed optic vesicle and the lens projecting into it, is that which is permanent in the majority of Gasteropods (vide fig.
It is the general opinion amongst the majority of investigators that the nervous ganglia in Gasteropods and Pteropods are formed from detached thickenings of the epiblast.
The larvae of Lamellibranchiata have in a general way the same characters as those of Gasteropods and Pteropods.
The ova of Gasteropods are exceptional in the fact that a vitelline membrane is rarely or never developed around them.
In prosobranchiate Gasteropods the larval shell is gradually added to, and frequently replaced by, a permanent shell, though the free-swimming veligerous larva may have a long existence.
In a very considerable number of cases amongst Gasteropods and Pteropods the auditory organs have been observed to develop as invaginations of the epiblast, which give rise to closed vesicles lying in the foot, e.
Amongst the Gasteropods and Pteropods there are present provisional renal organs, which may be of two kinds, and a permanent renal organ.
A pair of auditory sacks is found in the larvae of almost all Gasteropods and Pteropods, and usually originates very early.
In Gasteropods it is usually not filled with yolk, but contains a cavity, traversed by contractile mesoblastic cells.
A very characteristic type of unequal segmentation is that presented by the majority of Gasteropods and Pteropods and probably also of some Lamellibranchiata.
Gasteropods is developed from a mass of mesoblast cells close to the end of the intestine.
The above list will hopefully give you a few useful examples demonstrating the appropriate usage of "gasteropods" in a variety of sentences. We hope that you will now be able to make sentences using this word.
