**DRAFT**

KEY TO THE FRESHWATER MUSSELS OF PACIFIC DRAINAGES

Al Smith August 2004

> This key was developed to enable the user to identify mussels under
> three circumstances: a shell in hand, a live mussel in hand and a live
> mussel *in situ* underwater. As a result, there are a number of key
> characteristics for most species.
>
> Also included is a glossary for terms used in the key and a list of
> common names. John Fleckenstein generously contributed some cautions
> on using the key.
>
> Species in the genus Anodonta are difficult to separate. Shell
> characteristics are extremely plastic, depending on area found and on
> conditions such as water velocity and substrate. Some individuals
> cannot be identified by shell characteristics, even by an expert. In
> addition, taxonomy and ranges are not entirely settled. The
> characteristics listed below can be used to make a best guess about
> individuals, but identification should be confirmed by an expert. This
> requires collection of shells. The Anodonta species are not common in
> many areas of the Northwest. Taking live mussels is discouraged.

GENERA KEY

1.  Outline of shell triangular or round. Well-developed concentric
    sculpture lines,

> absent on other genera
> (introduced)..............................\...\...\...\...**Corbicula**

2.  Well developed pseudocardinal teeth. Ventral outline slightly
    concave. Nacre purple on fresh specimens. Arborescent incurrent
    opening papillae.
    ..............................................................................**Margaritifera**

3.  Distinct, heavy ridge running at an angle from umbo to posterior
    ventral surface.

Shell thick, heavy, sturdy. Divided, purplish incurrent opening
papillae.

.........................................................................................**Gonidea**

4.  Pseudocardinal teeth and heavy ridge absent. Shell thin, light,
    fragile.

> Single, whitish incurrent opening
> papillae................................**Anodonta**

SPECIES KEY

1.  Outline of shell triangular or round. Well-developed concentric
    sculpture lines. Adults small in size (to about 60
    mm)..........................**Corbicula fluminea**

# Widespread in streams, rivers, some standing water (introduced)

> Outline of shell elongate or oval. Adults larger than 60
> mm......................2

2.  Shell thick, heavy,
    sturdy...............................................................3

> Shell thin, light, fragile (genus
> Anodonta)............................................4

3.  Hinge lacking pseudocardinal teeth. Distinct, heavy ridge running at
    an angle from umbo to posterior ventral surface. Ventral outline of
    shell straight or

> broadly
> curved.......................................................**Gonidea
> angulata**

##  Pacific drainages from BC to CA, prefers gravelly bottom 

> Hinge with well developed pseudocardinal teeth. Shell with even
> surface; no distinct ridge. Ventral outline of shell slightly concave.
> Nacre purple on fresh
> specimens.........................................................**Margaritifera
> falcata**
>
> AK, BC, WA, OR, CA, MT, ID, NV, UT, WY, prefers gravelly bottom

4.  Shell length:height ratio usually 1.5 or less. Height of posterior
    half of shell

> greater than height of anterior half. Shell broadly ovate in
> outline...............5
>
> Shell length:height ratio close to or exceeding 2. Height of posterior
> half of
>
> shell nearly equal to height of anterior
> half...........................................6

5.  Shell with high, conspicuous wing. Shell outline compressed. Shell
    thinner

> than other Anodonta species................................**Anodonta
> nuttalliana**
>
> WA, OR, CA
>
> Shell with a wing of moderate height. Shell outline less compressed,
> especially
>
> in standing water. Shell comparable in thickness to other Anodonta
> species.
>
> .................................................................**Anodonta
> californiensis**
>
> BC, WA, OR, CA, ID, NV, UT, WY, AZ, Baja, Chihuahua

6.  Shell inflated only over anterior half of shell. Umbo clearly
    projects above hinge
    line...............................................................
    **Anodonta beringiana**

> AK, YT, BC
>
> Shell inflated primarily along posterior ridge of shell. Umbo does not
> or barely projects above hinge
> line.........................................**Anodonta kennerlyi**

BC, Alberta, WA, OR

> Shell primarily inflated over median portion of shell. Umbo does not
> project above hinge
> line................................................**Anodonta
> oregonensis**
>
> AK, BC, WA, OR, CA, NV, UT
>
> GLOSSARY
>
> Anterior---the shorter end of the shell from the umbo where the foot
> emerges
>
> Arborescent---tree-like, feathery
>
> Compressed---shells flattened together laterally
>
> Dorsal---the top of the mussel where the hinge and umbo occur
>
> Height---distance from the umbo to the ventral surface
>
> Hinge---the flexible attachment of the two shells on the dorsal side
>
> Incurrent opening---the ventral posterior opening where water flows in
>
> Inflated---swollen, expanded

### In situ---situated in a natural place or habitat

Length---distance between both ends of the mussel shell

Median---the line that divides an animal in half, in the middle

Nacre---the inner layer of the shell

Ovate---oval shaped

Papillae---small projections or protuberances

Posterior---the longer end of the shell from the umbo where the siphons
emerge

Pseudocardinal teeth---teeth inside the anterior part of the shell along
the hinge

Sculpture lines---raised narrow concentric ridges on the outside of the
shell

Umbo---raised part of the dorsal edge of each shell

Ventral---the bottom of the shell that can be opened

Wing---the thin, flat extension of the top of the shell on some mussels

COMMON NAMES

*Gonidea angulata*---western ridged mussel

*Margaritifera falcata*---western pearlshell

*Anodonta nuttalliana*---winged floater

*Anodonta californiensis*---California floater

*Anodonta beringiana*---Yukon floater

*Anodonta kennerlyi*---western floater

*Anodonta oregonensis*---Oregon floater