One of the big challenges of freshwater natural history is that it is hard to determine what exact animals were present in rivers before modern collections began. Preservation of pristine freshwater environments has been almost impossible as anything upstream affects everything downstream. Our zoological museums are a physical catalogue of the historical wildlife in an area and a guide for where our habitat reconstruction goals should be set.
Physical collections are fragile. It’s easy to lose data somewhere along the line and have the specimens themselves become nothing more than physical curiosities. It’s even easier to have an extensive and meticulous collection fall into the hands of disinterested heirs and be lost to us. Specimens need to be cared for properly to maintain their quality, and the longer it has been since they were collected, the less likely it is that the historical value is maintained. Occasionally these collections are saved via thoughtful preservation by some concerned individual or institution or, much less often, by a fortuitous fluke of storage through a period when, had it been accessible, it might well have been destroyed.
A collection of old labels, now dissociated from their original specimen.
A perfect example of this kind of fortuitous preservation is represented by two collections, The Hildreth and Holden Collections, currently located in our Bivalve Collection. These two collections were discovered together at Marietta College, Ohio. Few details exist today regarding the exact discovery, but some information has been preserved. Everyone directly involved with the discovery has, as far as I can tell, passed away long ago without publishing the details of the find.
It’s a weird twisting tale and, I believe, it deserves to be informally recorded here.
Our next post will fully detail the relevance of this collection and its history, but for now let’s just set the scene…
A little known fact about freshwater mussels is that they live part of their life as a parasite. The glochidia or larval stage of a mussel will attach to a host and grow for a few weeks before releasing and falling to the substrate below. The host that the glochidia parasitize is almost always a fish (there is one species of mussel that can parasitize salamanders). Each species of freshwater mussel has just a few species of fish on which its larva can attach. Because of this special and very specific mussel-host fish relationship, mussels have evolved ways to “trick” their particular fish into becoming infested with glochidia. Some mussel species lure fish in close with a modified section of their mantle tissue that resembles a tasty meal, such as minnows or tadpoles. When the fish strikes it is bombarded with thousands of glochidia, which will encyst onto the gills or other parts of the fish. The fish swims away, un-phased by the whole ordeal. The glochidia grow for 30 days or more on the fish. Another method a mom mussel uses to infest a host fish is by releasing a snot-like string containing their glochidia into the water. A fish swims through the strands and the larvae attach. Below are some examples of different mussel species using unique lures to attract their fish host.
Click the video below to view some examples of mussel lures.
Videos 1&2: Pocketbook (Lampsilis cardium) flapping its mantle tissue resembling a minnow or darter. This lure is used to attract fish such as smallmouth bass or bluegill on which the Pocketbook’s glochidia can attach.
Video 3: Ridged Pocketbook (Lampsilis ovata) displaying a similar lure as the Pocketbook mussel.
Video 4: Black Sand Shell (Ligumia recta) with its unique lure that to a fish looks and moves very much like a crayfish or crawdad. This lure could be used to attract fish such as largemouth bass. Interestingly, she usually displays the lure at night.
Video 5: Lilliput (Toxoplasma parvum) using undulating mantle flaps to lure in unsuspecting fish.
About the Author: Caitlin Byrne is Collection Manager of the Division of Molluscs.