#unionida

A mussel's hard outer shell already provides it with lots of protection, but Elliptio spinosa takes it to the next level! Altamaha spinymussels grow up to 5 spines in a row down the center of their shells, some of which can reach up to 2.5 cm (0.98 in) in length! In addition to extra predator deterrent, the spines also help the mussels to anchor themselves along the sandy river bottom.

Every species mussel uses fish to distribute their larvae-- except one. The salamander mussel is the only mussel which uses salamanders- specifically the mudpuppy salamander (Necturus maculosus)- as its host. Mussel larvae, or glochidia, attach themselves to the salamander's gills where they filter-feed until they metamorphose into adult mussels and drop off into their new homes.

Arkansas fatmucket (Lampsilis powellii)

...a rare species of freshwater Unionid bivalve which is endemic to the state of Arkansas in the United States, where it is known to occur in the Ouachita, Saline, and Caddo River systems. Arkansas fatmuckets typically occur in deep pools with enough water flow to remove debris. They are typically absent from areas with riffles or pools that lack waterflow. They prefer sandy substrates and are often seen next to river islands with strands of water willow (Justicia americana) present. 

Currently Lampsilis powellii is listed as Endangered as it is sensitive to environmental changes and only possesses a limited range. 

Classification

Animalia-Mollusca-Bivalvia-Unionida-Unionidae-Lampsilis-L. powellii

Reproduction In Unionids:

Unlike many bivalve taxa which simply release sperm and eggs into the water column, which will develop into trochophore larvae and eventually into veliger larvae which will settle in substrate. Unionids are unique in that they use a different life cycle to reproduce.

A Female Unionid will drawn in sperm from males into her gills, where fertilization will take place internally. The eggs produced from this will develop into Glochidium larvae. Later, when the female is ready she will use special lures known as superconglutinates, which are small-fish shaped extensions of her mantle, to draw fish in close. When said fish is close she will release her larvae which will then attach themselves to the fish's gills or digestive tract. From there they will feed on their host's bodily fluids for several weeks. They will then dislodge themselves and drop off their host. Next, they will develop into juveniles in the substrate and the process repeats itself.

The strategy is advantageous to the Unionids because of their chosen habitat. Most unionids occur in freshwater rivers where water moves downstream. Since bivalves are sessile they have no means to disperse upstream rivers, a problem marine bivalves don't face. By parasitizing fish glochidia can disperse against the current and access new feeding grounds.

Image: ©M. C. Barnhart 

Read More about Unionid reproduction [1] [2]

Amblema plicata

Sometimes known as the "Threeridge" A. plicata is a species of Unionid freshwater mussel that is native to North America, ranging from the coastal plain of the Gulf of Mexico west to Texas and north into the Mississippi River drainages. A. plicata is a generalist and will occupy a wide range of habitats, ranging from streams, to rivers, and even lakes. Like other bivalves A. plicata is a filter feeder and will filter the water around it for nutrients. 

Classification

Animalia-Mollusca-Bivaliva-Unionida-Unionidae-Amblema-A. plicata