Gastropods are single-shelled mollusk. They include conches, snails and turbans and are known for their spiral shells. They are far and away the largest group of molluscs. About 80 percent of the world’s 40,000 to 100,000 species of mollusks are gastropods. Gastropod means “stomach footed.” The “foot” is a disk used for creeping. On top of this a twisted hump, covered by mantle, which contains the digestive organs. Gastropods have a distinctive large head with two pairs of sense organs that look like horns or antennae and have eyes at their ends. They also have tentacles and a radula, ribbon-shaped tongue covered with rasping, microscopic teeth. Most have a shell which is attached to the body and completely covers it. The shape of the animal defines the shape of the shell.
Gastropods come in a wide variety of shapes, colors and sizes. Among the different kinds are: 1) limpets, who produce a pyramid-shaped shell from secretion released equally round the mantle; 2) snails, including whelks, turbans and conches, that create a spiral because the mantle secretes shell material faster one side than the other; and 3) cowries, which make a clenched-fist shell by secreting material from both ends of the mantle. Others create a twist turret by secreting material from only one side.
A typical gastropod has a spiral-shaped shell and moves by creeping along with a suckerlike foot. But not all gastropods fit this description. Some have no shell at all. Most gastropods have separate sexes. Some are hermaphrodites and some change sex during their lifetimes.
The largest gastropod is the trumpet conch of Australia. According to the Guinness Book of Records, one specimen found in 1979 had a 7.2 centimeters (30.4-inch) shell with a maximum girth of 100.33 (39.5 inches). It weighed nearly 18 kilograms (40 pounds) when it was alive. It found off of West Australia by a Taiwanese fisherman.
Websites and Resources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Fishbase fishbase.se ; Encyclopedia of Life eol.org ; Smithsonian Oceans Portal ocean.si.edu/ocean-life-ecosystems
Most gastropods have a single, usually spirally coiled shell into which the body can be withdrawn, but the shell is lost or reduced some important groups. Gastropods are characterized by torsion, a process in which the mantle cavity is rotated counterclockwise up to 180 degrees until it faces forward and is positioned over the head. This occurs early in larval development and means that the digestive, reproductive and excretory systems all discharge through the opening in the shell.”
flamingo tongue snail "Torsion" results in the gut and nervous system being twisted. According to Animal Diversity Web: Torsion takes place during the veliger stage, usually very rapidly. Veligers are at first bilaterally symmetric, but torsion destroys this pattern and results in an asymmetric adult. Some species reverse torsion ("detorsion"), but evidence of having passed through a twisted phase can be seen in the anatomy of these forms. Many snails have an operculum, a horny plate that seals the opening when the snail's body is drawn into the shell. [Source: Phil Myers and John B. Burch, Animal Diversity Web (ADW)]
Gastropods have a muscular foot which is used for "creeping" locomotion in most species. In some, it is modified for swimming or burrowing. Most gastropods have a well-developed head that includes eyes, 1-2 pairs of tentacles, and a concentration of nervous tissue (ganglion). Torsion in gastropods has the unfortunate result that wastes are expelled from the gut and nephridia near the gills. A variety of morphological and physiological adaptations have arisen to separate water used for respiration from water bearing waste products. /=\
Gastropods grow in a downward spiral by secreting new material along the edge of their lip. This produces a series of spirals. Each wider than the one above, that when viewed from the front appear to be stacked like the layers of classic Mayan pyramids, but unlike the pyramids built by humans the ones made by gastropods are built from the top down rather than the base upward.
Sea Snail Characteristics
Moon snails have a powerful foot that allows them to bulldoze along the sea bottom. When they come in contact with a clam they quickly pin it down with their foot. After that they secrete an acidic chemical on the shell to soften it up and then us their drill-like radula to chisel out a perfectly round hole. Finally the animal secretes some powerful digestive juice and sucks out the dissolving flesh. Their radula is like a long, ribbon-like tongue. It contains thousands of teeth (denticles) that project from the mouth opening.
According to Animal Diversity Web: A fully expanded animal is several times larger than its shell, which almost completely covers the body. Shell shape is globe-like, with shallow groove at the shoulder of whorls; columella with a calcereous callus reaching to edge of deep umbilicus. Shell color is yellowish with thin brown periostracum; the horny door (operculum) common to snails is dark brown. [Source: Dianne Hoehing, Animal Diversity Web (ADW) /=]
The snails plough forward with a foot just below the surface of the sand. When extended, the foot can measure over 12 inches in diameter. It is heavily ciliated, has mucus glands, and is very effective for moving over a shifting bottom. The mucus foot can fold into a grasping organ to hold prey. The foot also can be drawn inside the shell by an aquiferous system, but the snail cannot stay inside the shell for long periods of time because it cannot breathe. Life expectancy of this snail is estimated to be several years. /=\
Gastropod Feeding and Radula
Radula diagram Gastropods secure food with a hard, tongue-like devise known as a radula. The radula can take on many shapes and functions. In grazing species it is shaped like a file and used to scrape algae off the surface of rocks. In others it can shaped like a drill or even a barbed poison spear. The radula can take may forms. In grazing species it is shaped like a file and used to scrape algae. In others its shaped like a drill. Cone snails have transformed it into a kind of barbed spear that shoots small glassy, poison harpoons. [Source: Kevin Short, Daily Yomiuri]
Gastropods feed in a number of different ways although most species use their radula in some part of their feeding process. There are browsers, grazers and hunters. Some feed on plankton; some are scavengers or detritivores (mainly eat decomposed plants or animals); , some are active carnivores Some use their radula to scrape algae. Others hunt with radula modified into weapons. Whelks use the radula to bore into the shells of other mollusks. Some gastropods can eat through rock by secreting acid. And others swallow fish with a tube-like proboscises.
Methods used by moon snails to obtain food varies. They feed mostly on clams, mussels, or other mollusks and usually clamp their foot around clam shells and drill a hole with their radula (See above). It is believed that the foot smothers victims. According to Animal Diversity Web: Studies indicate there is an enzyme secretion of carbonic anhydrase that has a softening effect on mollusk shells to aid in drilling. Food is extracted by sucking the foot over the hole, or by sucking through the siphon of a clam. Young snails feed on diatoms, and on green seaweed called Ulva, at 10-12 meters depth for five to six months. Afterwards, they begin to hunt animal prey in the substratum. They do not venture into shallower water until their shell lengths reach about 30 millimeters. [Source: Dianne Hoehing, Animal Diversity Web (ADW) /=]
Gastropod Reproduction and Development
Some gastropods are hermaphroditic (have both male and female reproductive organs). Hermaphroditic forms exchange bundles of sperm to avoid self-fertilization. Copulation can be complex. In some species it ends with each individual sending a sperm-containing dart into the tissues of the other. Marine species have veliger larvae (final larval stage in which individuals have two ciliated flaps for swimming and feeding).
Male moon snails are smaller than females and their shells are slightly thicker. According to Animal Diversity Web: They begin to mate when they reach a shell length of 55 millimeters. Eggs are laid in a broad, rubbery "sand collar" about 15 centimeters diameter which forms around the shell and foot. This collar holds a layer of eggs (eggs are 250 micrometers in diameter) which is then deposited by ocean waves on the beach. The mucus collar is coated by layers of sand held together by the mucus. [Source: Dianne Hoehing, Animal Diversity Web (ADW) /=]
Moon snails lay eggs in shallow water in spring and summer, and eggs hatch in midsummer. A half-million or so larvae swim around inside the sand collar for several weeks until being released by disintegration of the collar. Young snails feed on diatoms, and on green seaweed called Ulva, at 10-12 meters depth for five to six months. Afterwards, they begin to hunt animal prey in the substratum. They do not venture into shallower water until their shell lengths reach about 30 millimeters. /=\
Types of Gastropods
Types of gastropods include limpets ,winkles, topshells, whelks, turbans, conches, cowries, cone snails, terrestrial slugs, terrestrial snails, sea slugs and sea hares.
Helmet shells are large and beautiful. They can be as large as 12 inches in length and are so named because they remind some of gladiator helmets. They live in sandy sediments and feed on other mollusks and sea urchins.
Murexes are a kind of snail that feed on other mollusks and barnacles by boring into their shells. Some look like snails with sharp spikes and are greatly sought after by collectors. Others secrete a purple substance that was prized in ancient times as a dye.
Conches are widely eaten in the Caribbean and other places. The animals are usually removed by making a cut in the shell, where the animal attaches itself, causing it plop out in a blubbery glob. To keep the shell in pristine condition, some people tie a string around the foot of the animals and hang it from a tree. The animals is slowly pulled out. After a couple days it stinks to high heaven and, with some species, the stretched out animals is almost a meter in length.
The violet sea snail is one of few gastropods found on the surface of the sea. It its kept afloat on a raft of made of mucus bubbles. It feeds on by-the-wind sailors and other floating hydriods.
Elizabeth Kolbert wrote in the New Yorker: Chrysomallon squamiferum, commonly referred to as the scaly-foot snail, is a mollusk that’s been found at vents in the Indian Ocean, at a depth of ten thousand feet (three kilometers). It’s the only animal known to build its shell with iron, and around its foot it sports a fringe of iron plates that looks a bit like a flamenco skirt. The snail carries around chemosynthesizing microbes in a special pouch in its throat. In 2019, Chrysomallon squamiferum became the first vent-dwelling creature to be included on the Red List of Threatened Species, maintained by the International Union for Conservation of Nature. The rationale for the listing is that the species has been found at only three sites, and two of these are being explored for mining. Its living space, the I.U.C.N. has observed, is thus apt to be “severely reduced or destroyed.” [Source: Elizabeth Kolbert, The New Yorker, June 14, 2021]
Worm snail shells are not like the typical coiled shells of most gastropods. Instead they have elongated tubular shells which are attached to hard ocean surfaces such as a rock, sponges or another shell. There are 135 species including scaled worm snail and jellyfish worm snails. The Fargo worm snail (Vermicularia fargoi olsson) has three spiral ribs on each shell whorl, which makes them very irregular, and unlike a regular snail shell. Fargo worm begin life in the normal coiled position. At this point there are about 2.5 centimeters (an inch) long. After that the shell starts to uncoil. When it acquires its mature irregular shape. The shell “tube” is about one centimeters (3/8 of an inch) in diameter. These shells reach a maximum length of eight centimeters (three inches). The first six shell whorls are typically regularly coiled with later whorls becoming detached from the shell. [Source: Nicholas Argent, Citrus Reef]
Lewis's moon snails (Scientific name: Euspira lewisii) live in western Pacific Ocean coast, from Vancouver Island in British Columbia in the north to Isla San Geronimo in Baja California in the south. They favor soft sand or mud in coastal areas, protected bays and low intertidal areas in waters less than 150 meters deep. More snails can be found at the surface at night than during the day. They are found at the surface after heavy rains, but remain buried in cold weather. [Source: Dianne Hoehing, Animal Diversity Web (ADW) /=]
On average Lewis's Moon Snail weigh is 435 grams (15.33 ounces) and have a shell up to 13 centimeters (five inches) in diameter, although usually they are 10 centimeters (4 inches) or less due to collecting by humans. They are cold blooded (ectothermic, use heat from the environment and adapt their behavior to regulate body temperature) and bilateral symmetry (both sides of the animal are the same). Sea snails are often found partially buried in the sand so that just part of their shell is visible above sand. They can plow easily through sand and normally avoid each other, but a feeding snail may attract other snails. /=\
Moon snails are eaten by humans and other animals. The California Fish and Game has set limits on the amount of moon snails taken, and none can be taken north of the Golden Gate Bridge in San Francisco.. The small crab, Opisthopus transversus, is sometimes found as a commensal of the snail, and hermit crabs are known to inhabit the empty shells. Lewis's Moon Snail has no No special status on the International Union for Conservation of Nature (IUCN) Red List:. They have no special status according to the Convention on the International Trade in Endangered Species (CITES). /=\
Volutes and Melon Shells— Much Sought After by Shell Collectors
Volutes are sought after by collectors. Most common in water around Australian waters, they are typically found in warm, shallow waters but also occur also in temperate seas. Most volutes burrow in sand and all are carnivorous. Most volute species have solid heavy shells but they vary greatly in size and appearance. They commonly are colorful, with an elongated aperture in the first whorl of the shell. All species have deep folds on the inner lip. [Source: Nicholas Argent, Citrus Reef]
Volutes have distinctive markings and a wide aperture. The name voluta means “forming a spiral curve or curves” in Latin. They have an inner lip with three or four plaits (grooves, teeth, or folds). They also feature an initial bulbous whorl at the apex of the shell, which looks like a shiny nub. You can find volute shells on coral sandy or muddy bottoms, mainly in deep waters of tropical seas.
Among the the more than 200 volute species are noble volutes, Philippine melon volutes and Indian melon volutes. The Imperial volute (Aulica imperialis) is arguably the most impressive volute. It is creamy white in color and has a brown cave drawing-type design on the surface and majestic spikes that resemble a crown of a king. Native to the Southern Philippines, it is usually found on sand in shallow water. They can reach a length of 25 centimeters (10 inches).
Melon shells are attractive sea shells that belong to the genus of volutes but differ slightly from other volutes. Melon shells belong to the genus of volutes but differ slightly. They are rounder and fatter giving them their melon shape. These sea creatures got their nickname “bailer shells” from their ability to hold large amounts of water, making them useful for bailing out boats if needed. Common types of melon shells include the volute lapponica, and Philippine melon. [Source: Heather Hall, AZ Animals, December 27, 2022]
Turbans and Sundial Shells
Turbos, also known as turbans, are top-shaped shells with a wide opening and pointed apex. They belong to the large family of Turbinidae, which consists of several hundred species found mainly in tropical seas. These mollusks are vegetarians that feed primarily on marine algae. These shells can have smooth to spiny surfaces and may be brightly colored or be muted white or grays. They are generally very durable but can break if exposed high temperatures for extended periods. They can live up to 40 years in the wild. Common types include pearl banded jade turbos, green jade turbos, the polished silver mouth and spotted turbo. [Source: Heather Hall, AZ Animals, December 27, 2022]
Sundial shells are colorful species and are fairly unique in being having noticeably flattened, disc or cone-shaped shells. The cone-like shell coils up from a flat base. Their spirals are composed of vibrant shades of black, white, and brown. They get their name from their resemblance to sun dials. Also called staircase shells "Architectonicidae" have a world-wide distribution in warm-temperate to tropical waters. They dwell in shallow sandy areas and are usually seen at night, but are rarely found on the shore. [Source: Nicholas Argent, Citrus Reef]
There are more than 140 sundial shell species. Among them are Architectonica karsteni, variegated sundial shell and Partridge sundial snail. The Perspective sundial shell (Architectonica perspectiva) are a beautiful species. Once common throughout most of their range, they are now much less common due to uncontrolled shell collecting and destruction of their habitat.
Miter shells are colorful shells found in the tropical Indo-Pacific region. They get their name from their resemblance to a miter (a bishop’s headwear). The miters from the Indo-Pacific are more colorful than those from Eastern Pacific, which tend have more muted colors. Many miters are smooth while others are ornamented with spiral ribs. All have a narrow aperture. The siphonal canal is usually very short and the outer lip may be toothed, smooth or corrugated. [Source: Nicholas Argent, Citrus Reef]
There are more than 500 species of miter shell. They include the Pontifical miter, Episcopal miter and Queen mite The pontifical miter (Mitra stictica) can reach a length of about eight centimeters (2.5 inches) and has a thick, bullet-shaped shell with five to eight whorls and a high and pointed spire. Also known as the pontifical miter or sungkod-sungkod, it is found in the Indian Ocean off Aldabra, Chagos, the Mascarene Basin, Mauritius and Tanzania, and in the Pacific Ocean off Fiji, New Zealand, and the Solomons. This species is similar to mitra papalis, but its body is shorter, and the sutures are farther apart and nodules.are narrower.
Image Source:s Wikimedia Commons, NOAA
Text Sources: Animal Diversity Web (ADW) animaldiversity.org; National Oceanic and Atmospheric Administration (NOAA) noaa.gov; Wikipedia, National Geographic, Live Science, BBC, Smithsonian, New York Times, Washington Post, Los Angeles Times, The New Yorker, Reuters, Associated Press, Lonely Planet Guides and various books and other publications.
Last Updated April 2023