fat threeridge: is this mussel strong enough to take on human destruction? — Species Account

Reflecting back on the mission statement of this blog series, the words endangered and animal don’t always mean beautiful tigers, killer whales, or chimpanzees. The vast majority of the world’s endangered species aren’t that large and most aren’t mammals. Some are very small, like the Topeka shiner we learned about in the last species account, and other animals hardly seem like animals at all. For example, mussels are one group of animals that rarely get the attention that they deserve. Living a seemingly passive and sessile life, mussels live in waterways all around us, but these creature seems to lack the pizzazz they need to rattle the public outside of beach shell collectors and mussel cuisine enthusiast.

fat threeridge

(Amblema neislerii)


To me, the fat threeridge sounds like a name they forgot to finish, but in actuality it is a fascinating freshwater river mussel that historically inhabited southern Georgia and Florida. Specifically, they are endemic to the Apalachicola river system. Residing in the muddy, silty, and sometimes sandy bottoms of shallow rivers beds, this mussel prefers rivers with a moderate current in sizes big or small. The fat threeridge lives its life a lot like other mussels in that part of its life is a parasitic lifestyle and the other part is spent attached to river substrate.

In the first stages of life, the glochidia, or rather the mussel’s larva stage, attaches to the gills or fins of a host fish to develop and be carried to other parts of the river for dispersal. When released from the mother mussel in the summer months, she sends a white sticky web-like mass with them, allowing the glochidia to attach to the fish. This white goop expands and wraps around a fish assisting in the attachment. The preferred host fish are usually different types of minnows and different species in the sunfish family. The glochidia undergoes a full metamorphose into a juvenile mussel in 10-14 days at which point they release from the fish and settle into their primary habitat. Upon arrival at their new primary habitat, the fat threeridge will become essentially motionless and, assuming the habitat is suitable for their survival, the juveniles will grow into adults where they will continue their sessile livelihoods. Although some passive movement downstream may occur during heavy currents, the only voluntary movement that the fat threeridge makes is to burrow deeper into the substrate. And let me tell you, as an organism that looks pretty similar to a rock, it’s a pretty incredible journey to watch.

Aquarium Burrowing Clam www.youtube.com

To the everyday river explorer, the fat threeridge is going to be very hard to find and distinguish from other mussels. The Fat threeridge is usually less than four inches in its length and its width. It’s shell is thick and heavy and can vary a bit in the curvature. Like many other freshwater mussels, the outer appearance is dark brown to black for camouflage, but the fat threeridge has 7-9 parallel horizontal folds in the shell making it unique in comparison to some of its neighbors. The fat threeridge inner shell is an iridescent bluish white to purple color that is reminiscent of a pearl.


All mussels are filter feeders, meaning they eat by filtering food from out of the water. The particles of food suspended in the water become trapped when filtered through the mussel and then they are consumed. Most of their diet is made up of plankton and other dead organic material, however, some of these mollusks can be ruthless! Although they look like passively feeders, the adults have been known to eat full earthworms and other invertebrates as well! Even the glochidia can eat a variety of aquatic invertebrates and crustaceans. When in captivity, the glochidia have also been able to eat small tadpoles, which I can imagine would be quite a feat.

Up next we will discuss the environmental issues that the fat threeridge faces: fat threeridge: is this mussel strong enough to take on human destruction? — The Environmental Issue

If you would like to check out more animals on the Endangered Species List on your own, please visit the U.S. Fish and Wildlife Service’s list of Threaten/Endangered Species in the U.S. and Foreign Countries.

Bogan, A.E. Amblema neislerii. The IUCN Red List of Threatened Species 1996: [Online] 1996. http://dx.doi.org/10.2305/IUCN.UK.1996.RLTS.T1076A3214210.en. (accessed Apr 3, 2017).

Wisniewski, J. Fat threeridge (Amblema neislerii). Georgia Dpt. of Nat. Resources: Wildlife Resources Division. [Online] 2008 http://www.georgiawildlife.org/sites/default/files/uploads/wildlife/nongame/pdf/accounts/invertebrates/amblema_neislerii.pdf (accessed Apr 3, 2017).

Florida Fish and Wildlife Conservation Commission. Fat Threeridge (Mussel). Florida Fish and Wildlife Conservation Commission. [Online] 2011 http://myfwc.com/media/2211661/Fat-Threeridge.pdf (accessed Apr 3, 2017).

Image 1: Biggins, D. Amblema plicata. https://upload.wikimedia.org/wikipedia/commons/5/57/Amblema_plicata.jpg (accessed Apr 3, 2017).

Image 2: Miller, M. Weird Nature: Flexing Mussels. http://19mvmv3yn2qc2bdb912o1t2n.wpengine.netdna-cdn.com/wp-content/uploads/2012/05/fat-threeridge-mussel-cgs.jpg (accessed Apr 3, 2017).

Video 1: Marco Fish. Aquarium Burrowing Clam. https://www.youtube.com/watch?v=6JyNpPUj1ys&w=560&h=315 (accessed Apr 3, 2017).

Image 3: sarvicant8. Three-ridged, Fat. https://www.fws.gov/athens/images/fatthreeridge2.jpg (accessed Apr 3, 2017).

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