Page 8 - The Freshwater Mussels of Oklahoma
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Excretory System
The kidney is the principle organ of excretion. It is located below the heart and is
connected to the pericardial chamber. Pericardial fluid passes through the kidney and
waste materials are removed. Wastes eventually pass into the suprabranchial chamber
and out the excurrent siphon.
Circulatory System
The blood is basically a clear fluid with only a few amoebocytes being the only
cellular elements present. The heart consists of two auricles and one ventricle . The
ventricle surrounds the lower intestine just anterior to the rectum. Blood collects in the
auricles and passes into the ventricles. From the ventricles, blood passes through the
body through the anterior and posterior aortae and their branches. Blood collects in
venus sinuses (large veins) and returns to the heart.
Nervous System
There is no concentrated “brain” present. There are several nerve centers called
ganglia located in various regions. There are two cerebral ganglia near the mouth that
are in turn connected to two pedal ganglia in the foot and also with two visceral ganglia
in the posterior region below the posterior adductor muscle.
Sensory System
Since cephalization (an organized head) is not well developed in mussels, there
are no organized sensory organs present. However, there are at least chemoreceptors,
thermoreceptors and photoreceptors present so the animal is capable of responding to a
variety of stimuli.
Reproductive System
The reproductive process in the unionids is a very complex and interesting
process. Typically, there are separate sexes (dioecious). However, monoecious
individuals have been reported in the genus Anodonta (Utterbackia). The gonads are
located in the region above the foot and tend to surround much of the intestine. In the
male, sperm pass into the surabranchial chamber and are discharged into the water via the
excurrent siphon. The sperm must then be taken into the incurrent siphon of a female for
fertilization to occur. In females, the eggs are transferred to the water tubes in various
regions of the gills. Fertilization occurs in the gills of the female and the fertilized eggs
are retained in the gills for further development into a tiny bivalve called a glochidium.
The glochidium must be discharged from the gills and at this point must attach to a fish
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