This conclusion has shown that the Euthyneura do not represent an archaic form of Gastropoda, but are themselves derived from streptoneurous forms. The difference between the two sub-classes has been shown to be slight; certain of the more archaic Tectibranchia (Actaeon) and Pulmonata (Chilina) still have the visceral commissure long and not untwisted.
The Pulmonata are, like the other Euthyneura, hermaphrodite, with elaborately developed copulatory organs and accessory glands.
In aquatic Pulmonata the osphradium is retained.
In some Pulmonata (snails) the foot is extended at right angles to the visceral hump, which rises from it in the form of a coil as in Streptoneura; in others the visceral hump is not elevated, but is extended with the foot, and the shell is small or absent (slugs).
Pulmonata are widely distinguished from a small number of Streptoneura at one time associated with them on account of their mantle-chamber being converted, as in Pulmonata, into a lung, and the ctenidium or branchial plume aborted.
- A Series of Stylommatophorous Pulmonata, showing transitional forms between snail and slug.
The Pulmonata have a straight visceral nerve-loop, usually no operculum even in the embryo, and a multidenticulate radula, the teeth being equi-formal; and they are hermaphrodite.
Some Pulmonata (Limnaea, &c.) live in fresh waters although breathing air.
The lung-sac serves undoubtedly as a hydrostatic apparatus in the aquatic Pulmonata, as well as assisting respiration.
The same general range of body-form is shown in Pulmonata as in the Heteropoda and in the Opisthobranchia; at one extreme we have snails with coiled visceral hump, at the other cylindrical or flattened slugs (see fig.
The adaptation of the Pulmonata to terrestrial life has entailed little modification of the internal organization.
The generative apparatus of the snail (Helix) may serve as an example of the hermaphrodite apparatus common to the Pulmonata and Opisthobranchia (fig.
Other Pulmonata exhibit variations of secondary importance in the details of this hermaphrodite apparatus.
The shell of the Pulmonata, though always light and delicate, is in many cases a well-developed spiral " house," into which the creature can withdraw itself; and, although the foot possesses no operculum, yet in Helix the aperture of the shell is closed in the winter by a complete lid, the " hybernaculum," more or less calcareous in nature, which is secreted by the froot.
The nautiloid shell In Planorbis and in Auricula (Pulmonata, formed on the larva allied to Limnaeus) the olfactory organ is being cast, and a new on the left side and receives its nerve from shell of a different form the left visceral:ganglion.
The development of the aquatic Pulmonata from the egg offers considerable facilities for study, and that of Limnaeus has been elucidated by E.
Other Pulmonata possess, when embryos, Stiebel's canals in a more fully developed state, for instance, the common slug Limax.
Whilst the Pulmonata are essentially a terrestrial and fresh-water group, there is one genus of slug-like °:ti FIG.
Pulmonata with an external shell.
Pulmonata with two pairs of tentacles, except Janellidae and Vertigo; these tentacles are invaginable, and the eyes are borne on the summits of the posterior pair.
The commonest land-snails are those species which constitute the family Helicidae, order Pulmonata, sub-order Stylommatophora.
The term "water-snails" includes the whole of the remaining sub-order of the Pulmonata, namely, the Basommatophora, in which the eyes are sessile, with the exception of the Auriculidae.
Thus the whole of the Pulmonata (which breathe air, are destitute of gill-plumes and operculum and have a complicated hermaphrodite reproductive system) are either snails or slugs.
The species of Helix are all herbivorous, like the Pulmonata generally; snails and slugs are well-known enemies to the gardener.
Orders: Pulmonata, Nudibranchia, Inferobranchia, Tectibranchia, Heteropoda, Pectinibranchia, Tubulibranchia, Scutibranchia, Cyclobranchia.
Orders: Heterobranchia, Dermatobranchia, Heteropoda, Ctenobranchia, Pulmonata, and Cyclobranchia.
They agree with the dorsal eyes of Oncidium (Pulmonata) in the curious fact that the optic nerve penetrates the capsule of the eye and passes in front of the retinal body (fig.
They are best developed in the Pulmonata; in some cases they are very rudimentary and may be destitute of an external opening.