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Terrestrial
Gastropods of the Columbia Basin, British Columbia
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| Terrestrial
Gastropods in British Columbia
Terrestrial, or land, gastropods -- hereafter referred to as snails and slugs -- occur almost everywhere in British Columbia, from alpine meadows, screes, coniferous mountain forests and valley lowlands to urban gardens and parks. We notice larger species during wet weather in particular, but as a rule, slugs and snails are small, shun light and seek cool, moist places under logs, rocks and vegetation, making them difficult to find. The hard, spiral, calcareous shell of snails capture the interest of naturalists, and gardeners are likely to be very familiar with those species regarded as pests because of their insatiable appetites. Several species of terrestrial molluscs also serve as intermediate hosts for nematode parasites of ungulates (Blood 1963; Boag & Wishart 1982). The snails and slugs of British Columbia have never been adequately documented. The primary source of information for this region is Pilsbry's four-part monograph (1939, 1940, 1946, 1948). This work, however, provides little information pertaining to British Columbia and the information is dated and often difficult to use. Publications since Pilsbry are scattered in various scientific journals and deal only with a few taxa or other geographic areas. Popular literature on the group is almost nonexistent. This report is part of the Living Landscapes
Project (1997 to 1999), sponsored by the Royal BC Museum (RBCM)
and the Columbia Basin Trust to study the natural and human history
of the Columbia River Basin (also known as the Kootenays). Given
the paucity of information on terrestrial gastropods in British
Columbia, a study of this kind seemed timely. The RBCM's collections
revealed several species of snails and slugs not found elsewhere
in the province. This Website provides identification aids to the
species in the region and brings together information on their biology,
ecology and distribution. What are Terrestrial Gastropods? Snails and slugs belong to the phylum Mollusca, a large and diverse group of non-segmented invertebrate animals living in the ocean, freshwater and on land. The largest subdivision of the Phylum Mollusca, Class Gastropoda (the gastropods), includes several well-known examples: snails, slugs, limpets, conchs and nudibranchs. Gastropods have a distinct head with tentacles and eyes, and a broad, flat foot for locomotion. There is a visceral mass dorsally, which is at least partially covered by a mantle. The mantle encloses a mantle cavity that either contains gills for respiration or is modified to form a "lung". The visceral mass is usually protected by a calcareous shell. The three subclasses of gastropods are based on the form and position of the respiratory organs, as well as on other anatomy. Members of the subclass Prosobranchia have gills located in front of the heart. Prosobranchs, such as limpets, abalones and whelks, live in marine, freshwater and terrestrial environments, but the majority are marine. There are relatively few terrestrial prosobranchs and none occur in British Columbia. The subclass Opisthobranchia has gills located behind the heart. All opisthobranchs, including the shell-less sea slugs, and some shelled forms, are marine. The subclass Pulmonata include mostly land snails and slugs, but a few are found in freshwater or in the sea. The mantle cavity of terrestrial pulmonates is modified into an organ capable of breathing air. All the terrestrial molluscs in British Columbia are pulmonates. The three Orders within Pulmonata are defined by the number of pairs of tentacles, the position of the eyes on the head, and other anatomical details. The Basommatophora have one pair of tentacles with an eye at the base of each. The group occurs mostly in freshwater but a few are terrestrial. Carychium is the only basommatophoran genus in British Columbia. The largest order, Stylommatophora, has two pairs of tentacles with the eyes at the tip of the upper pair. The tips of Stylommatophoran tentacles can be retracted inside the tentacle. Most terrestrial molluscs belong to the Order Stylommatophora. Systellommatophora is a relatively small group of slugs with no representatives in British Columbia. Like stylommatophorans, this group has a second pair of tentacles with eyes at their tips; however, the tentacles can be contracted but not retracted. Terrestrial slugs are gastropods with a reduced shell that in most groups is internal. Slugs belong to several unrelated lineages, since shell reduction and a tendency towards a sluglike form has evolved several times within the gastropods. |
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BC Museum |
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