Modern Gastropod
Harpa ventricosa
(Ventral Harp Shell)
from Cebu, Philippines
Fossil Pelecypod
Venericardia densata
from Stone City Formation
Burleson County, Texas

Conchology is the branch in zoology that deals with the study of mollusks and shells.

PMNS has a number of pages where shells are displayed and there is information. Below are pages on this website, which you may want to visit .

Links in this website to MODERN SHELLS see Modern Shells; Cebu; Corregidor; Philippines

Links in this website to FOSSIL SHELLS:Fossil Shells; Stone City Formation, Burleson County, Texas; Leisey Shell Pit, Ruskin, Florida

What are shells? Basically they are the homes for creatures called snails.

Shells come in two basic types of structures: Univalves or Gastropods AND Bivalves or Pelecypods.

There is another basic division into two parts: Modern shells and Fossil shells.

There is yet another basic division of shells into three parts: Marine shells, Fresh Water Shells and Land snails.

There are about of Gastropods and . Gastropods are the type of shells you see which have an opening in the shell, which usually curls around in ever larger curls and has a covering made of a flexible, but hard material to cover the opening.


Gastropods, of which there are about 105,000 known species, have a single, shell that is usually coiled, closed at one end, often ending in a point, and open on the other end, with a closing valve. Gastropods have a distinct head with tentacles and a rasping tongue called a radula. Most of the species have shells, but not all.

About have of Gastropod species are marine and the other half are either terrestrial or fresh water. In most marine species, the sexes are separate. Larva, which are free-swimming, emerge from eggs laid by the parent in the water. Larva eventually grow into a shelled adult. Five years is the average life expectancy of a gastropod. However, some are known to have lived for 30 years

Gastropods may be carnivorous, herbivorous or parasitic. One of the ten most deadly things alive are some species of conus shells which have a poison dart on the tip of their radula, or tongue. They slowly approach another snail, fish or other marine life, then strike with this poison dart, much like a rattlesnake (using the tongue only, not the body as a snake). The poison is so deadly that a person picking up such a shell with a bare hand, being hit by this deadly radula, may not live to get to shore.

When you see a Pelecypods shell with a hole in it, it is probably put there by a Gastropod using its radula as a rasp to drill a hole in the shell, then eat the Pelecypods inside.


Pelecypods, of which there are about 20,000 known species, consist of two "valves", i.e. halves, which are usually pretty much equal in size and shape. This valves are convex on the outside and concave on the inside. The two valves meet at a hinge, which is the fulcrum upon which they close. They close by way of an adductor muscle anchored to each of the two vales, or halves of the Pelecypods. Opposite the hinge, is the opening side, which sometimes has an irregular edge, with so-called teeth, i.e. a toothed or jagged edges on both valves, which fit together when closed, making for a tighter seal, than smooth edges would.

About two-thirds of Pelecypods are Marine and one-third are fresh water. Pelecypods make up most of the shells which we eat, including including clams, mussels, oysters and scallops.

Pelecypods lack a head and radial teeth. They feed on microscopic plant life aided by their gills. They are excellent in filtering bacteria and other undesirable things out of the water and do a pretty good job of disposing of them. However, on occasions folks get really sick when the Pelecypods have in their bodies, pathogens which are dangerous or deadly to humans, especially when the Pelecypods (such as oysters) are eaten raw.

Pelecypods sexes may be combined in one individual or may be separate. Most lay their eggs directly into the water.

If you are interested in seeing good really great modern shells, here are a couple of sources which sell shells, but also picture many beautiful modern sea and land shells:

LINKS for shell Aficionados

Those in the Houston, Texas area may like to connect with the Houston Conchology Society. Their web site is http://www.houstonshellclub.com/

My friends, Guido T. Poppe and Philippe Poppe, web site http://www.conchology.be/index.php, own Conchology, Inc. You can subscribe to their website for FREE and they will send you out lists AND PICTURES of thousands of beautiful shells which they have for sale. They also periodically send out under water pictures of marine life which you will really enjoy.

Another site which we have just visited, and obtained some information on shells, which also provides photos of many beautiful modern shells is Sea Shell World Com, whose web site is http://www.seashellworld.com.