Pulmonates (Air Breathing Land Snails)

Description:

In the Pulmonata subclass, the species hallmark is a functional lung, which the term, "pulmonate" refers to. The mantle cavity walls have become heavily vascularized and more or less form a lung sac ("pallial lung"). By expansion and contraction of the mantle muscles, this lung sac permits breathing air across a small opening to the outside. Thus, oxygen and carbon dioxide gases can exchange with the vascular system, and none of the pulmonate snails have (or needs) the gill.

Additional specializations have come about, as well. Since water conservation on dry land is paramount, their excretory systems have become adapted to reduce water loss. Nitrogenous wastes, for example, are converted into uric acid which is then excreted as a crystalline solid waste, like that of birds and reptiles.

The Pulmonata fall into two groups consisting of several orders. The seventh order, Systellommatophora, comprises slug-like land gastropods, which will not be dealt with here.

First, the land group, which includes Stylommatophora and three other orders (Mesurethra, Heterurethra, and Sigmurethra) (see the Pulmonata link, below, for classification details). The land group is by far the most abundant and found in terrestrial habitats, varying from desert to moist locations. About 30,000 species, including 600 genera and 14 superfamilies are included.

Second, the freshwater water group (Basommatophora and Archaeopulmonata orders). These snails occupy muddy freshwater streams and moist land habitats. About 4,000 species and 48 genera are included. They also do not have an operculum and are fully adapted for air breathing. Eyes mounted at the base of the tentacles distinguish the freshwater group, whereas in the Stylommatophora and related orders, the eyes are mounted at the tips of retractile tentacles (Morton, 1960).

In the Sorbeconcha Clade, a few air breathing species are also found, which attests to the remarkable evolutionary adaptability of molluscs. These snails have an operculum, unlike the Pulmonata, which do not. Some genera seem to have evolved in successive stages from marine, to freshwater, to exclusively air breathing terrestrial species.

Here, several groups have a mantle cavity that has become partitioned into both a gill chamber and a lung. For such amphibious species, it appears more efficient at times to extract oxygen directly from the air, than it is to extract it from stagnant surface water by means of a gill. The double chambered mantle cavity is found among several genera in the Rissoidae, Valvatiidae, and other families.

Other prosobranchs have become functionally similar to terrestrial pulmonates, with a complete loss of the gill (Morton, 1960). They include genera in the following families: Helicinidae (Neritoidea superfamily), Cyclophoridae (Cyclophoroidea superfamily), and Pyrazus ebeninus in the Thiaridae family (Cerithioidea superfamily).

Classification (see Gastropod Classification pages for more complete detail)

Land Snail Families, exhibited on this web site:

Subclass: Pulmonata

Orders: (several)

Families:

Air Breathing Operculate Snails, exhibited on this web site:

Clades: (several)

Families:

Papuina pulcherrima (Rench, 1931)
Green Tree Snail
(from Solomon Islands)
Family: Camaenidae
Subclass: Pulmonata

Polymita picta (Born, 1778)
Painted Helix
(from Cuba)
Family: Xanthonichidae
(syn., Helminthoglyptidae)
Subclass: Pulmonata

SEE OTHER LAND SNAIL FAMILIES
(AIR-BREATHERS)

Pulmonata
Photo Gallery

SEE AN AIR-BREATHING
MARINE SNAIL:

Pyrazus ebeninus
Thiaridae Family

Land Snails (& other Air-Breathers in Pulmonata Subclass & Sorbeconcha Clade)