Gastropods

Beautiful Mollusks

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The Institute for Marine Mammal Studies

(IMMS) is a non-profit organization established

in 1984 for the purpose of public education,

conservation, and research of marine mam-

mals and sea turtles in the wild and under hu-

man care. Located in Gulfport, MS, IMMS has

been an active participant in the National

Stranding Network since its inception. IMMS is

the premiere organization in the Mississippi-

Louisiana-Alabama sub-region of the Gulf

Coast with the capability and experience to

care for sick and injured marine mammals and

sea turtles. Additionally, IMMS promotes public

awareness of marine conservation issues

through its involvement in the community.

Institute for Marine Mammal Studies P.O. Box 207, Gulfport, MS 39502

Phone 228-896-9182 Fax: 228-896-9183 Email: contactus@imms.org

Website: www.imms.org

Quick Facts Gastropods are mollusks and are related to squid,

octopus, and cuttlefish.

There are over 62,000 species of gastropods.

The Queen Conch can live as long as 40 years.

The study of mollusk shells is called conchology.

Cowrie shells were once used as currency in many Polynesian cultures.

The venom from the “sting” of some cone snails can be fatal to humans.

REMEMBER

Prepared by Chris Breazeale, 2012

References: World Register of Marine Species

University of California Museum of Paleontology

www.mesa.edu.au

www.paleo.cortland.edu

Gastropod reproduction varies greatly among spe-

cies. Hermaphroditism is common in all but the

marine species, with individuals serving as either

male or female during mating. The shape of the

shell can often determine the manner in which the

gastropod mates. Snails with tall shells use a

mounting technique while snails with flat shells

often mate in a face-to-face fashion. All gastro-

pods, however, reproduce through internal fertili-

zation. In some instances, sperm can be stored

for months or years before being used to fertilize

eggs. Mates are located through touch and the

use of pheromones, or by sensing cues in the mu-

cus trail left by terrestrial slugs. Most gastropods

are oviparous (egg laying). Land snails deposit

eggs in nests dug in

moist soil. Many

aquatic gastropods

deposit their eggs in

a gelatinous mass

containing as many

as 40,000 individu-

als. During spawn-

ing season, some

gastropods can lay

eggs in intervals of

one or two days.

Others, however, lay

much smaller clutch-

es (groups of eggs)

two or three times

each season. More

common are the

“mermaid’s necklac-

es” laid by the

whelks. These long

chains of egg cases

can be found on

beaches throughout

the world. Juvenile

gastropods are often

called protoconchs

and are shaped like

the adults.

Gastropods are categorized into groups called

clades. Clades are groups of organisms that have

descended from a common ancestor. There is

much discussion in the scientific community re-

garding the biological grouping of some species.

The clades listed below are generally recognized

by researchers.

Neritopsina contains fresh-

water, saltwater, and terrestri-

al species. They can be

found in all shapes and sizes

from limpet-like, to coiled

shells, to slugs.

Vetigastropoda includes

keyhole and slip-limpets,

top shells, abalone, and

several other families.

Caenogastropoda is a large

group that includes many

marine species often coveted

by shell collectors. Conchs,

whelks, moon snails, murids,

cowries, and many others

belong to this group.

Heterobranchia includes

opisthobranchs (sea hares,

sea slugs, and bubble shells)

and pulmonates (consist of

more than 20,000 species).

Patellogastropoda are true

limpets, historically called

Docoglossa. This a major

group of marine gastropods.

Cocculinidae are white lim-

pets that attach to organic

matter in the deep ocean.

This brochure is funded with qualified outer continental shelf oil

and gas revenues by the Coastal Impact Assistance Program,

United States Fish and Wildlife Service, U.S. Department of the

Interior through a grant award to the Mississippi Department of

Marine Resources.

Class: Gastropoda

Reproduction

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Phylogeny

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Kingdom: Animalia

Phylum: Mollusca

Class: Gastropoda

Scientific Classification

The Basics Gastropods represent a group of animals often

called snails or slugs. Meaning “stomach foot,”

the word gastropod describes the muscular “foot”

that runs along the underside of the snail. This

foot is used primarily for locomotion. Many gas-

tropods have a shell but some do not. The shelled

gastropods are often called univalves because

they only have one shell, as opposed to bivalves

which have two shells. Some of these animals are

terrestrial, living their entire lives on land. Like

all other mollusks, other gastropods live in marine

or freshwater habitats. There are approximately

62,000 described species and 13,000 genera of

gastropods found throughout the world, from the

neighborhood garden to deep-water hydrothermal

vent colonies. Current estimates place the num-

ber as high as 150,000 species. They comprise

80% of living mollusk species. Gastropods are

extremely diverse in morphology (shape), feeding

behavior, reproductive strategies, habitat range,

and size. They have the widest range of ecologi-

cal niches of all mollusks. Gastropods are among

the oldest known fossils, with their shells being

found in rocks dating 540 million years ago.

Many species today have remained unchanged for

over 350 million years.

Many gastropods have a shell that protects the soft body of the animal. The coiled shell opens on the right-hand side in most species and many species possess an operculum (gill cover) that further helps to protect the animal. Gastropods exhibit anatomi-cal torsion. This means the visceral (muscle) mass

rotates 180⁰ to one side during development, plac-ing the anus above the head. Gastropods typically have a well-defined head and two to four sensory tentacles with eyes located near the base of the ten-tacles or on separate eye stalks. The eyes of uni-valves are extremely diverse, with some possessing simple ocelli (simple eyes) which cannot process images, to eyes containing lenses for nocturnal species. The feeding habits of gastro-pods are varied, though most species utilize a radula (tongue-like structure). Rad-ulae are chitinous ribbons designed to scrape or cut food before it enters the esophagus. Both herbivo-rous (plant eating) and carnivorous (animal eating) snails use a radula for feeding. Some species even use their radula as a “drill” to bore into the shells of other mollusks before consuming their prey. Other univalves may be detritus (decaying organic matter) feeders, scavengers, or ciliary (tiny hairs) feeders. The primary organs for excretion are the nephridia. These organs produce ammonia or uric acid as a waste product. Most marine gastropods breathe using a gill but some freshwater species and most terrestrial species have a pallial lung (lung sac). Nudibranchs often have feathery gill plumes located on their backs.

Anatomy Gastropod shells

are essentially

exoskeletons.

The primary

functions of a

shell are to pro-

tect the animal

from predators and pro-

vide a place for muscle attachment. The shell is

also useful in the prevention of mechanical dam-

age. Terrestrial snails use the shell for protec-

tion against the sun and to prevent desiccation or

drying of the bodily fluids. Secreted by the man-

tle, the shell is composed mainly of calcium car-

bonate precipitated into an organic matrix

known as conchiolin. Due to the asymmetrical

nature of coiled shells, gastropods possess a

quality known as chirality or “handedness.”

Over 90% of gastropods have a dextral or “right-

hand” shell. Left-hand coiled shells are referred

to as sinistral. If the opening (aperture) of a

shell is on the right side when the shell is held

with spire pointing upwards, the shell is said to

be dextral. Occasionally, dextral species will

produce sinistral shells, and vice-versa. These

oddities are highly sought after by shell collec-

tors. There are a few species of arboreal (tree-

dwelling) land snails that show normally mixed

coiling, with individuals being either sinistral or

dextral. Not all shelled gastropods exhibit coil-

ing. Limpets, especially, are known to have

simple cone-shaped shells as adults.

Many gastropods are

used as food items

throughout the world.

Conchs in particular

are highly sought after

due to their mild fla-

vor, especially in the

Caribbean and the

Florida Keys.

Escargot, abalone, and

periwinkle snails are also

popular food items.

Throughout history,

seashells have been

used as ornamenta-

tion, scrapers, cooking

utensils, oil lamps,

boat bailers, musical

instruments, and even

currency. The world-

wide seashell trade has devastated populations

of gastropods, leading some countries to ban

the import and export of some shells. The

more endangered species have been fully pro-

tected in some areas, making it illegal to collect

or harvest these animals. In parts of the Carib-

bean, countries are now “farming” gastropods

like the queen conch to try to satisfy public

demand for meat and shells. The collection of

seashells is considered by some to be harmless.

Many beaches around the world are comprised

of shell material and animals such as the hermit

crab, rely solely on the discarded shells of gas-

tropods for survival. Although empirical data

from the trade of seashells are

hard to find, it is estimated

that billions of dollars each

year are made collecting and

selling shells around the

world.

Various Gastropod Shells ucmp.berkeley.edu

Pink Queen Conch Lobatus gigas naplesseashellcompany.com

Live Conch out of Shell members.virtualtourist.com

Co

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Cayenne Keyhole Limpet Diodora cayenensis

Green abalone Haliotis fulgens shells-of-aquarius.com

Hermit Crab in Shell hermitcrabpetcare.com http://njscuba.net

The freshwater Sinistral Pond Snail (Physella sp.) scrapes algae from the

glass with its radula ucmp.berkeley.edu

Shells Human Impacts