Carychium exiguum

Geographic Range

Carychium exiguum , the obese thorn snail, is native to the Nearctic region. It ranges north from Newfoundland to central Manitoba (areas including Alberta, New Brunswick, Nova Scotia, Ontario, Quebec, and Newfoundland), west to New Mexico and the Sierra Madre mountains in Durango, Mexico, south to Costa Rica, and east to the Atlantic coast. It is common through the middle and eastern United States, and in many states is the most abundant species of land snail. This species has also been recorded in central Oregon. In Michigan, obese thorn snails may be found throughout the state.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

Obese thorn snails are found in very damp (but not frequently flooded) areas, such as floodplains, swamps, and moist woodlands. They are considered to be hygrophilous. These snails are generally found in areas with moss, ferns, and plant debris, in shaded areas such as under leaf litter or rotting logs.

In Michigan, three macrohabitats have been described for this species: small depressions in cypress ( Thuja sp.) forests, grasslands (possibly former Thuja sp. forests), and hardwood forests.

• Habitat Regions
• temperate temperate
• terrestrial terrestrial

• Terrestrial Biomes
• forest forest

• Wetlands
• marsh marsh
• swamp swamp
• bog bog

Physical Description

Obese thorn snails have translucent to whitish elongate shells, which are 1.2 to 2.5 mm tall, with about 4.5 convex whorls. The columular lamella, found at the left side of the aperture, is S-shaped (curving down and then up). There is a small tooth on the parietal wall of the shell opening. The aperture lip is thickened and reflected.

The soft anatomy of obese thorn snails consists of a smooth integument and a single pair of contractile tentacles with no pigmentation at the base. Eyes are located at the base of the tentacles. This species has no pedal groove, but does have a reproductive groove. These snails have approximately 100 transverse rows of teeth on their radular membranes. Sixteen teeth are located on either side of the median tooth. The radula is covered with a thick cuticle.

• Other Physical Features
• ectothermic ectothermic
• heterothermic heterothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Development

In general, land snails deposit their eggs in moist areas. Snails in the genus Carychium have a shell gland, which produces a leathery coating for the eggs. Timing for egg hatching depends on moisture and temperature, and some individuals may develop much slower than others, even if they hatch at the same time. Evidence suggests that populations of these snails in Michigan grow throughout the summer after hatching and attain near adult size by mid-fall. The snail reabsorbs the shell partitions and the shell's lamellae form during the post-embryonic stage. Thickened, reflected lips at the aperture indicate maturity.

Reproduction

Carychium exiguum is hermaphroditic, and mainly reproduces by cross-fertilization. Although specific stimuli are not known, basommatophoran snails, such as obese thorn snails, may be cued to mate by encounters with other partners, increased temperatures, and/or changes in photoperiod. Two snails may locate each other through mucus trails. After a courtship ritual, snails copulate, with each snail inserting spermatophores into the other.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

Obese thorn snails likely hatch in late spring or early summer and reach maturity in the fall, particularly in temperate areas such as Michigan. Thickened, reflected lips at the aperture indicate maturity. These snails are oviparous and produce about three eggs during a reproductive cycle.

• Key Reproductive Features
• iteroparous iteroparous
• seasonal breeding seasonal breeding
• simultaneous hermaphrodite
• sexual sexual
• fertilization fertilization
  • internal internal
• oviparous oviparous

Land snails leave eggs after they are deposited and do not exhibit any parental care.

• Parental Investment
• no parental involvement
• pre-fertilization
  • provisioning

Lifespan/Longevity

The lifespan of Carychium exiguum is likely about one year; there is evidence that mortality is highest in late summer/early fall, mainly for juveniles.

Behavior

Light intensity, relative humidity, and temperature influence much of a land snail's behavior, since these factors affect the snail's water retention. In general, land snails are nocturnal, and more active with increased relative humidity and decreased temperature. In temperate climates, an epiphram will form over the shell's aperture as the snail aestivates over the winter. During dry periods, this same membrane will form to prevent dessication. Several individuals of this species are usually found together, under leaves. They are negatively phototactic.

When crawling, the head of an obese thorn snail emerges from the base of the shell aperture; the shell is elevated with its columnar axis at about 45 degrees. The shell moves slightly side to side as the animal goes forward and the tip of the tail jerks slightly. These snails move slower when wet, and may lope to avoid rough substrates or to retain water.

• Key Behaviors
• terricolous
• nocturnal nocturnal
• motile motile
• sedentary sedentary
• aestivation
• social social

Home Range

Home ranges of land snails vary, but smaller species such as obese thorn snails may have home ranges of 10 square meters or less.

Communication and Perception

Carychium exiguum has sensory tissue at the tips of its tentacles and anterior margin of the labial palps. Land snails leave mucus trails which are used as a form of communication. The mucus allows the snails to detect individuals of their own and other species. They also have eyes located at the bases of their tentacles and are negatively phototactic.

• Communication Channels
• tactile tactile
• chemical chemical

• Perception Channels
• visual visual
• tactile tactile
• chemical chemical

Food Habits

An obese thorn snails uses its radula, a toothed feeding organ, to scrape or grind food. These snails likely feed on decaying plant material and fungi.

• Primary Diet
• mycophage mycophage
• detritivore detritivore

• Plant Foods
• leaves

• Other Foods
• fungus
• detritus detritus

Predation

Specific predators are not known for this species, but in general, land snails are preyed on by lampyrid beetle larvae or other insects, birds, rodents, and small mammals, particularly voles and shrews.

Ecosystem Roles

Generally, land snails disperse fungal spores and plant seeds, and break down detritus in the forest. While some land snails are vectors for nematodes, none are currently recorded in the literature for this species. Carychium exiguum also serves as prey to a variety of species, including insects, birds, and small mammals.

• Ecosystem Impact
• disperses seeds
• biodegradation biodegradation

Economic Importance for Humans: Positive

There is no known positive effects of Carychium exiguum on humans.

Economic Importance for Humans: Negative

There are no known adverse effects of Carychium exiguum on humans.

Conservation Status

Obese thorn snails have not been evaluated by the International Union for the Conservation of Nature and Natural Resources and hold no special conservation status.

Other Comments

The family Carychiidae is sometimes recognized as a subfamily of the family Ellobiidae . The taxonomy of species found within the genus Carychium is still under review.

Additional Links

Encyclopedia of Life

BioKIDS Critter Catalog

Contributors

Renee Mulcrone (author), Special Projects, Angela Miner (editor), Animal Diversity Web Staff.

References

Bashynski, S. 2008. " Carychium exiguum (Say, 1822)- Obese Thorn" (On-line). BioWeb. Accessed December 15, 2013 at http://bioweb.uwlax.edu/bio210/2011/bashynsk_sara/index.htm .

Burch, J., Y. Jung. 1988. Land snails of the University of Michigan biological station area. Walkerana , 3/9: 1-177.

Burch, J., T. Pearce. 1990. Terrestrial gastropoda. Pp. 201-310 in Soil Biology Guide . New York: John Wiley and Sons.

Geraerts, W., J. Joosse. 1984. Freshwater snails ( Basommatophora ). Pp. 141-207 in The Mollusca , Vol. 7, reproduction. London: Academic Press, Inc.

Harry, H. 1997. Carychium exiguum (Say) of lower Michigan; morphology, ecology, variation and life history ( Gastropoda , Pulmonata ). Walkerana , 9/21: 1-104. Accessed August 19, 2013 at http://molluskconservation.org/WALKERANA/Vol9/walkerana%20vol9%20no21%201-104.PDF .

Hubricht, L. 1985. The distributions of the native land mollusks of the Eastern United States. Fieldiana, Zoology New Series , 24: 1-191. Accessed August 19, 2013 at http://www.archive.org/stream/distributionsofn24hubr/distributionsofn24hubr_djvu.txt .

IUCN, 2013. "The IUCN Red List of Threatened Species. Version 2013.2" (On-line). Accessed August 19, 2013 at http://www.iucnredlist.org/search .

Miller, B. 1970. The Sandahl molluscan fauna (Illinoian) from McPherson County, Kansas. Ohio Journal of Science , 70/1: 39-50. Accessed December 15, 2013 at https://kb.osu.edu/dspace/bitstream/handle/1811/5512/V70N01_039.pdf?sequence=1 .

Nekola, J. 2005. Geographic variation in richness and shell size of eastern North American land snail species. Records of the Western Australian Museum , Supplement 68: 39-51. Accessed December 15, 2013 at http://sev.lternet.edu/~jnekola/nekola%20pdf/rwam-68-39-51.pdf .

Nekola, J. 2012. The impact of a utility corridor on terrestrial gastropod biodiversity. Biodiversity and Conservation , 21: 781-785. Accessed August 19, 2013 at http://sev.lternet.edu/~jnekola/nekola%20pdf/bc-21-781-795.pdf .

Pearce, T. 1989. Loping locomotion in terrestrial gastropods. Walkerana , 3/10: 229-237. Accessed August 19, 2013 at http://www.carnegiemnh.org/uploadedFiles/CMNH_Site/Mollusks/Downloads/Pearce1989.pdf .

Perez, K., J. Cordeiro. 2008. A guide for terrestrial gastropod identification. Terrestrial Gastropod Identification Workshop, 1: 1-72. Accessed December 15, 2013 at http://www.uwlax.edu/biology/faculty/perez/Perez/PerezLab/Research/Publications/AMS_Workbook_KEP_FINAL.pdf .

2003. " Carychium exiguum " (On-line). Encyclopedia of Life. Accessed May 16, 2013 at http://eol.org/pages/453022/overview .