The Oregon Seal Oregon Department of Fish and Wildlife  
 »ODFW Home    » Fish Division   » Marine Resources   » Recreational and Commercial Shellfish   » Bay Clams   » Bay Clam Identification
About Us Fishing Hunting Viewing License/Regs Conservation Living With Wildlife Education
Commercial and recreational marine fisheries
Bay Clams
Bay Clam Identification


A number of clam shell features are used to identify clams. Shape and size are usually coupled with exterior and interior design of shells to positively identify clams. From above the sand, clams can also be identified by the hole their neck leaves in the sand as the tide recedes. This is commonly referred to as a show. Each species of clam has a slightly different show that can be identified. The size of the clam and distance from the surface also contributes to its appearance.



Most commonly harvested species | Other commonly harvested species

 Most commonly harvested species

Gaper clam Butter clam Native Littleneck clam Cockle
Common name Gaper Butter Native Littleneck Cockle
Other names

Empire, horseneck, blue

Scientific: Tresus capax

Beefsteak, Martha Washington, quahog

Scientific: Saxidomus giganteus

Steamer, native littleneck

Scientific: Leukoma staminea

Heart cockle, Nutall's cockle

Scientific: Clinocardium nuttallii

Key Identification Features

Large gape around neck and concentric shell rings.

Largest common clam in Oregon estuaries.

Commensal pea crab pairs are often found within their mantle.

Identified by its smooth concentric  rings.

Thick and heavy oval shell

Identified by concentric lines and radiating ridges

Longer lived and less abundant than cockles.

Circular in shape.

Identified by their prominent radiating ridges.

Circular in shape.

Common size



1½-2 ½”


Common habitat

High salinity areas of sand or mud.

High salinity areas of sand, mud, gravel, or rock

High salinity areas of sand, mud, gravel, or rock.

High salinity areas of sand.


gaper show

Produce the largest clam show. Their necks are often visible within the show, as pictured above.

butter clam show

Usually described as long and narrow, as if a flathead screwdriver had been stuck in the sand.


cockle show

Typically look like two pencil holes next to each other.

 Other commonly harvested species

  soft shell clam purple varnish clam rough piddock flat tipped piddock
Common name Softshell Purple varnish clam Rough piddock Flat tipped piddock

Other names

Mud clam, eastern softshell

Scientific: Mya arenaria

Mahogony clam

Scientific: Nuttallia obscurata

Piddock, rock oyster

Scientific: Zirfaea pilsbryi

Piddock, rock oyster

Scientific: Penitella penita

Key Identification Features

Concentric rings and oblong egg shape, slightly pointed at the neck end.

Identified by its varnish like coating and purple interior.

Native to Japan, introduced to Oregon in the 1990s.

Identified by gape at neck end and teeth (for burrowing) at foot end.

Distinguished from the rough piddock by the "callum"- the smooth area on the lower foot area of the shell.

Common size





Common habitat

High to low salinity areas of mud.

Mid salinity areas of sand.

High salinity areas of clay, mud or sandstone. Most common in high salinity portions of bays.

Nearshore rocky areas


softshell show

Tend to be approximately circular but can sometimes be oblong.





About Us | Fishing | Crabbing & Clamming | Big Game Hunting | Game Bird Hunting | Wildlife Viewing | License / Regs | Conservation | Living with Wildlife | Education | Workday Login

ODFW Home | Driving Directions | Employee Directory | Social Media | | File Formats | Employee Webmail | ODFW License Agents | Accessibility

4034 Fairview Industrial Drive SE   ::   Salem, OR 97302   ::    Main Phone (503) 947-6000 or (800) 720-ODFW [6339]

Do you have a question or comment for ODFW? Contact ODFW's Public Service Representative at:
Share your opinion or comments on a Fish and Wildlife Commission issue at:
Do you need this information in an alternative format or language? Contact 503-947-6000 or click here.

   © ODFW. All rights reserved. This page was last updated: 10/27/2023 1:40 PM