Pennsylvania Land Snails
Here are some words used frequently in the study of land snails. For more terms, see Burch, 1990. Primary reference: Burch (1962).
Photo: Neohelix albolabris, Ed Thompson
anal pore—opening in the mantle to allow waste elimination.
aperture – the opening of a snail shell from which the snail's soft body emerges, sometimes called the "mouth."
apex—the top end of a shell's columella, opposite the umbilicus and furthest from the aperture.
axial—a direction parallel to a shell's columella.
basal—the bottom or floor of a shell's aperture or shell when viewed apex up, umbilicus down.
breathing pore—an opening in the mantle to allow air passage. Also called the pneumostome.
callus—a thickening in the shell wall.
caudal—a direction referring to the tail.
columella—the central, structural axis of a snail shell. At the top of the columella is the shell's apex and at the bottom, the shell's umbilicus (though it may be covered).
dart – a tiny calcareous spear injected into a potential mate’s flesh prior to copulation.
denticle—a solid calcium carbonate deposit integral to a land snail shell, usually at the aperture or within the shell. Denticles are often referred to as "teeth," and are supposed to aid in shell positioning, predator deterrence, or calcium provisioning.
dextral—a direction meaning whorled to the right. A dextral shell's aperture appears on the right to an observer when the shell is positioned with apex up and umbilicus down and aperture toward the observer. All of Pennsylvania's land snails are normally dextral.
epiphragm—a membrane of dried mucus formed across the aperture of a snail shell, it helps to prevent dessication when the snails is inactive for long periods.
foot—the muscular organ whose contractions propel a land snail, the foot is located on the ventral surface of the animal's soft body.
genital pore—the opening to a land snail's reproductive organs, usually located on the right side of the head behind the right eye tentacle. Most of Pennsylvania's land snails are hermaphroditic, so the genital pore provides access to both a vagina and extendible penis.
granulose—a shell texture that appears as many small raised bumps.
impressed—a shell groove or indentation.
iteroparous – life history in which adult snails have more than one reproductive cycle.
keel—a longitudinal ridge on the top of a snail or slug’s tail.
lamella—an elongated denticle or "tooth" located at the aperture or within a snail's shell.
malacologist – a scientist who studies mollusks (the Phylum of animals that includes land snails).
mantle—the membrane–like organ that builds the shell in shelled snails, found around the aperture. The mantle is also present in slugs, where it serves as a dorsal covering.
microsculpture—shell surface shapes and textures often requiring magnification.
nuclear whorl – the part of a land snail’s shell formed in the egg prior to hatching, sometimes with a unique microsculpture pattern.
odontophore – cartilage structure in the mouth over which the radula is drawn to rasp food.
operculum – a hardened cover that closes the aperture of a shell, present only in one Pennsylvania terrestrial species, Hendersonia occulta, and the amphibious species Pomatiopsis lapidaria.
oviposition – egg laying.
palatal—a direction referring to the part of a shell aperture away from the columella when viewed apex up, umbilicus down.
pneumostome—an opening in the mantle to allow air passage. Also called the breathing pore.
radial—a direction perpendicular to a shell's apex, like the spokes of a wheel.
radula—a chitinous organ in the mouth of a snail, covered with series of tiny teeth that function to rasp food.
semelparous – life history in which adult snails mate once and then die.
sinistral—a direction meaning whorled to the left. A sinistral shell's aperture appears on the left to the observer when the shell is positioned with apex up and umbilicus down. None of Pennsylvania's land snails, excepting anomalies, exhibit this character.
spermatophore – a sperm packet exchanged during mating.
spermoviduct – a canal in the reproductive system through which sperm move and in which fertilized snail eggs are developed.
spiral—a direction parallel to a shell's direction of whorl growth
spire—the part of a snail shell above the final full whorl.
suture—the seam at which sequential whorls of a shell meet.
tentacle—one of two to four elongate, retractable sensory appendages at the snail's head; they are devoted to chemoreception and most have eyespots as well.
umbilicus—the depression at the base of a snail shell, leading into the interior space of the columella. The spire may be open; perforate, very tiny; or closed, covered by shell material.
ventral—direction meaning lower or underside.
whorl—each 360 revolution of a snail's shell, measured from the apex.
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