Evergreen Natural History Database

This key is for use on those bivalves found on or along the Geoduck Beach at The Evergreen State College's campus on Eld Inlet, Olympia WA.

1
(a)  Is the body worm-like, no greater in circumference than a pencil, with a greatly reduced shell that covers only a small portion of the soft parts? Was it found tunneling into wood with a pair of calcareous, featherlike pallets, used for closing the off the burrow, located on the siphon….. Teredinidae

(b)  Body not as described in 1a….. 2

2
(a) Are the valves of the shell unequal in size and/or shape with one valve commonly, but not always, cemented to a solid substrate….. 3

(b)  If both valves of the shell are convex and similar in size and shape, and the shell isn’t permanently cemented to the substrate (although, the animal may be attached by a byssus)..... 4

3
(a)  If the lower (attached) valve of the shell is very thin, conforms to the shape of the substrate, and has an obvious hole through which the byssus (which attaches the animal to the substrate) exits….. Anomiidae

(b) If the lower (Attached) is not thin, though it may still conform to the shape of the substrate, and is permanently cemented to the substrate….. Ostreidae

4
(a)  Does the interior of shell have two adductor muscle scars, one each in the posterior and anterior ends of both valves?  If the anterior scars are small and barely noticeable, the umbones are near the anterior portion of the shell and the animal is attached to a solid substrate by a group of byssal threads….. Mytilidae

(b) Does the interior of the shell have two adductor mussel scars; one each in the posterior and anterior ends of both valves? If the two scars are of similar size (although shape may vary), the umbones are near the middle of the shell margin and the hinge has teeth, a chondrophore or both….. 5

5
(a) Is the majority of the shell covered with radial sculpting?..... 6

(b) If the shell is without any radial sculpting….. 7

 6
(a)  If the length of the shell is less than the height or at least not noticeably greater than the height….. Cardiidae

(b)  If the length of the shell is noticeably greater than the height….. Veneridae

7
(a)  Does the interior of the left valve have a spoon-like chondrophore projecting from the hinge plate while the right valve has a recessed chondrophore?  If the hinge plates of both valves lack lateral teeth and the hinge ligament is internal….. Myidae

(b)  If the shell lacks a projecting chondrophore on either valve but does have a large bowl-like chondrophore recessed into the hinge plate of each valve and hinge teeth….. 8

8
(a)  When looking at the hinge plate: if there is only a single tooth and the shell is large (may exceed 15 cm in length) and generally rectangular, but still not large enough to encompass the huge siphon (which can reach up to one meter in length when extended) when retracted and gapes widely all along the ventral shell margin….. Hitellidae

(b)  If the hinge plate has multiple teeth and the shell is generally less than 10 cm long but still large enough to encompass the retracted siphon and gapes only at the posterior end if at all….. 9

9
(a) If the shell gapes widely only at the posterior end and the shell length is 12 cm or greater….. Mactridae

(b) If the Shell doesn’t gape or only gapes slightly at the posterior end and nowhere else and the shell length is generally less than 10 cm….. 10

10
(a) If there are three cardinal teeth on both hinge plates….. Veneridae

(b)  If there are only two cardinal teeth on both hinge plates….. Tellinidae