The marsh periwinkle, Littorina irrorata, is an abundant snail in the salt marshes of the western Atlantic. The shell is elongate conic in shape, longer than it is wide (Andrews 1994). Coloration of the shell is dull grayish white with tiny dashes of reddish brown on the ridges of the spiral. Eight to ten gradually increasing flat whorls comprise the shell, with the body whorl measuring about half of the total height. The aperture is oval with a sharp outer tip and regular grooves on the inside edge.

Littorina irrorata is found in salt marshes that extend from Long Island, New York, south along the coast to central Florida. L. irrorata is also found of west of Florida extending along the Gulf Coast to Texas.

Biogeographic Regions: nearctic ; atlantic ocean

The distribution of L. irrorata is mainly limited to salt marsh habitats of the India River Lagoon, mostly confined to the northern areas of the lagoon. In south Florida, including the southern areas of the India River Lagoon, L. irrorata is largely replaced by the mangrove periwinkle, L. angulifera (Kaplan 1988). Age, Size and Lifespan: The maximum age of L. irrorata is unknown, and the lifespan can vary with food availability and environmental factors. The maximum reported shell length for the marsh periwinkle is 3.2 cm (Kaplan 1988), but most individuals are around 2.5 cm (Andrews 1994).

The shell size of Littorina irrorata ranges from 19 mm to about 32 mm high. The shell is thick and broad. The aperture is oval in shape. The shell is shaped like an elongated cone, being longer than wide. Usually a grayish white color, it has tiny, short streaks of reddish brown on the spiral ridges. The shell is also opaque and dull. The columella and callus is usually a pale reddish brown color and the outer lip of the shell is stout, sharp and usually has tiny regular grooves on the inside edge. The inside of the sharp outer lip is marked with red-brown streaks. The whorls on the shell are almost flat and it has about 8 to 10 whorls, which gradually increase. The shell may have a greenish tinge from fine algal growth.

Range length: 19 to 32 mm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Many of the species of littorinids common to the western Atlantic are found in the IRL, including: the mangrove periwinkle, Littorina angulifera; slender periwinkle, L. angustior; lineolate periwinkle, L. lineolata; white-spot periwinkle, L. meleagris; and the zebra periwinkle, L. ziczac. All of these species share a similar shell shape and an intertidal distribution. The mangrove periwinkle attains a shell length of about 2.5 to 3.0 cm, and varies in background color from bluish white, orange to dull yellow, reddish brown to grayish brown (Andrews 1994). The shell is comprised of 6 whorls, with the body whorl about half of the total height of the snail. Darker dashes on the ribs of the shell are often fused to form stripes on the body whorl. The early whorls around the base bear regularly-spaced vertical white spots below the channeled sutures. The slender periwinkle is relatively small, reaching a length of about 0.8 cm (Abbott 1974). The upper whorls of the shell are marked with 6-9 spiral lines, the sides of the foot are mottled black and gray, and the operculum is mostly round in shape. The lineolate periwinkle reaches a length of about 1.2 to 2.5 cm, has a gray background color on the shell with oblique zigzag lines of dark brown, and an apex of reddish brown (Andrews 1994). The shell is composed of 6-8 gradually increasing whorls, with the body whorl spanning more than half of the total length, and the suture between whorls is well marked. The pear-shaped aperture has a sharp, thin outer lip meeting the body whorl at an acute angle. Shells of males are smaller and more strongly sutured then females.The white-spot periwinkle is also small like the slender periwinkle, measuring about 0.8 cm in length (Abbott 1974). The shell has a pointed spire with a thin periostracum or organic covering. The aperture is reddish brown and the exterior of the shell is brown with large, irregular white spots, often arranged in spiral roles.The zebra periwinkle has a shell length of about 1.3 cm, and is whitish with dark brown or black wavy stripes (Andrews 1994). The aperture is small and oval, and the operculum is chitinous. This species is often confused with L. lineolata, but has a lighter colored shell with a narrower apical angle than the lineolate periwinkle.Regional Occurrence & Habitat Preference: The marsh periwinkle ranges from New York to Texas (Abbott & Morris 1995, Bequaert 1943), and shares a similar distribution with the salt marsh cordgrass, Spartina alterniflora (Hamilton 1978). Individuals are found above the water line on and around vegetation throughout salt marsh areas (Hutchens & Walters 2006), often on dead, upright leaves of Spartina alterniflora (Crist & Banta 1983). Occasionally, populations are found on jetty rocks and seawalls (Gosner 1978).

Littorina irrorata is found in brackish water marshes and can be found on marsh grass living at or above the water level. It is usually associated with marsh plants in the genus Spiratina.

Habitat Regions: saltwater or marine

Aquatic Biomes: coastal ; brackish water

Wetlands: marsh

Other Habitat Features: estuarine ; intertidal or littoral

Littorina irrorata is an herbivore that feeds mainly on algae. It grazes over the surface of marsh grass, usually Spiratina species. Members of the genus Littorina are known to move in response to chemical emanation from food at a distance.

Plant Foods: algae

Other Foods: detritus ; microbes

Primary Diet: herbivore (Algivore); detritivore

The marsh periwinkle is herbivorous, grazing on algae, fungi and the marsh cordgrass, Spartina alterniflora (Andrews 1994, Bärlocher & Newell 1994, Graça et al. 2000, Gustafson et al. 2006, Hutchens & Walters 2006, Silliman et al. 2004, Warren 1985).Predators: Documented predators of L. irrorata include: the squareback marsh crab, Armases cinereum; Atlantic mud crab, Panopeus herbstii; blue crab, Callinectes sapidus; and the crown conch, Melongena corona. (Buck et al. 2003, Schindler et al. 1994, Silliman et al. 2004, Warren 1985). Additional predators of the marsh periwinkle likely include large fishes, birds and mammals.

When predators are removed, periwinkles feed heavily and negatively impact Spartina, a marsh plant.

Ecosystem Impact: biodegradation

Littorina irrorata is preyed on by fish, crabs (particularly blue crabs), birds, sea urchins, and small mammals. In Connecticut, research found diamondback terrapins also fed on this species.

Known Predators:

• fish (Actinopterygii)
• crabs (Decapoda)
• blue crabs (Calinectes sapidus)
• sea urchins (Echinoidea)
• small mammals (Mammalia)
• diamondback terrapin (Malaclemys terrapin)

No known obligate associations exist for L. irrorata. However, marsh periwinkles are associated with several organisms common to salt marshes and other intertidal areas. For extensive lists of other species found in the habitats in which L. irrorata occurs, please refer to the "Habitats of the IRL" link at the left of this page.

The marsh periwinkle can reach high densities in the salt marshes of the east coast of North America. In many areas, populations range between 15 and 66 individuals m-2 (Hutchens & Walters 2006, Schindler et al. 1994). However, when left unchecked be predators, they may approach densities over 2,600 snails m-2 (Hutchens & Walters 2006).

The eye structure of Littorina irrorata have been described. Eyes are lateral to the cephalic tentacle. The animal is able to detect light and motion.

Experiments found the snails preferred vertical bars over horizontal bars, suggesting they can see and sense plant stems, where they are usually found in nature. Another study found L. irrorata positively reponds to plant odors found in its environment.

Communication Channels: chemical

Perception Channels: visual ; tactile ; chemical

Nothing was documented about the species but about the genus. In a closely related species, Littorina littorea, the embryo hatches as a veliger larva. The planktonic distributive larval stage has been eclipsed. Littorina neritoides and L. littorea eggs are set free singly into the plankton hatching as veligers. In L. littoralis, the eggs are laid in gelatinous layers attached to the substratum, hatching at the crawling stage. In L. saxatlis, the young merge at the crawling stage as viviparous forms and the young remain protected within the maternal body. In L. angulifera, a veliger larva is expelled.

Information is not known.

Most of what is known about reproduction is for the genus Littorina. In some species of Littorina, the males are not only smaller than the females but their shell has a more elongated spire and narrow aperture. In this genus fertilization occurs internally. The delivery of the spermatozoa into the mantle city of the female would be rendered more efficient if the ciliated pathway were extended on to a projection from the body of the male. It is natural, therefore, that a penis bearing a lateral ciliated seminal groove should develop on the right side of the male. In many mesogastropods and in the hermaphrodites in which exchange of sperm cannot be reciprocal since male and female aperture are widely separate, the partners orientate themselves in the same direction and the male may the female, settle on the right side of the body, and even be carried about by her, as in Littorina spp. Some Littorina spp. (e.g. L. littorea, L. neritoides) have pelagic capsules extruded from an ovipositor situated near the genital aperture in a position comparable to that of the penis. Here the capsule receives its final form and its outer layers harden the contact with seawater. The ventral wall of the pallial oviduct usually fails to develop glands and so provides an easy pathway for the sperm. The female L. irrorata is known to produce floating egg capsules.

Key Reproductive Features: sexual ; fertilization (Internal ); oviparous

Females lay eggs and no parental investment is involved thereafter.

Parental Investment: pre-fertilization (Provisioning)

Reproductive strategies are quite diverse within the Littorina genus. Some species release egg masses from with larvae hatch, others attach egg masses to hard substrata, and some brood their young until giving birth to larvae or juvenile snails (Ruppert & Barnes 1994).

US Federal List: no special status

CITES: no special status

Periwinkles are sensitive to toxic agents and are used for toxicology studies.

Positive Impacts: research and education

Ecological Importance: High densities of marsh periwinkles have the potential to drastically reduce coverage of their main food source, the cordgrass, Spartina alterniflora. As a top predator of L. irrorata, the Atlantic mud crab, Panopeus herbstii, helps to keep snail populations in check that could otherwise decimate salt marsh vegetation (Silliman et al. 2004).