Unionid
Mussels
in Kansas |
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L-R: Bleufer, Pistolgrip and a
young Pocketbook
from the Fall River near New Albany, Kansas
Photo by Jim Mason |
Clockwise from
top: Neosho Mucket, Butterfly, Western Fanshell and Ouachita Kidneyshell. All these
species are on the threatened and endangered species list in Kansas. They were found
in the Verdigris River in Montgomery County, Kansas.
Photo by Ed Miller |
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 | Mussels are in the Family Unionidae, Class Bivalvia within
the Phylum Mollusca. Mollusks are a very diverse
group that might not seem to be related. Mussels are cousins to the squid,
octopus, nautilus, snail and slug! |
| Unionid Mussels (also known as naiades or freshwater mussels)
have bilateral symmetry. The two shell halves or valves
are identical in size and proportions. The only difference between the valves is in
the structure of the area where the shells fit together. The valves typically have
two kinds of interlocking structures that serve to hold the shell together and protect its
resident. These are called lateral teeth
and pseudocardinal teeth,
and can be seen in the following images of a Mapleleaf. The exact shape and size of
these structures are important in keying out species. The area between the
lateral and pseudocardinal teeth is called the interdentum.
Collectively, these three features are called the hinge. |
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Pseudocardinal teeth of a Mapleleaf |
Lateral teeth of a Mapleleaf |
| Mussels can move, but verrrry slowly! They
have a muscular "foot" that they can protrude out between the valves, wedge into
the substrate on the stream bottom and then contract to pull the animal a short
distance. This process is then repeated if the mussel wishes to move some
more. Mussels can use this method to either move sideways or vertically. Some
mussels can be fairly active. Other species may spend their whole lives in one
spot. One fun thing to do is look for the mussel trails of the "frisky"
types in shallow water. The trails resemble what you would see if you took a stick
and drew a squiggle with it. If you follow the trail, you will find the animal at
one end or the other, usually in a small depression. |
| Most species of mussels have a parasitic stage of life that
requires a suitable host fish. The eggs develop within the female
mussel in a specially modified gill pouch called the marsupium.
They are released as a larval form called glochidia,
which must attach themselves almost immediately to either the gills or fins of the proper
species of fish. This apparently does no harm to the host fish. Some unionids
may use more than one species of fish as a host and others only a single species.
(One notable exception is the Salamander Mussel [Simpsonaias ambigua], which uses
a type of salamander called the Mud Puppy for the host instead of fish. Also, at
least one species of unionid does not have a parasitic stage.) The glochidia mature
into juvenile mussels, burst out of their cyst and drop to the bottom to begin their adult
life. This is the principal means that unionid mussels use to disperse into new
territory. They have no other way to move upstream in a watershed, other than by the
slow creeping action referred to above. |
Several species of mussels have very interesting methods for getting a fish close
enough to ensure they will be infected with glochidia. Some wave a lure called a
mantle flap, which usually looks like a small minnow, but in one species it resembles a
crawdad! When a predator fish tries to nab what it thinks is a meal, the mussel
squirts a bunch of glochidia into its mouth!
Others carry deception a step further. They form their glochidia into gummy
little packets that look like tiny fish or aquatic insect larvae and release them into the
water. These packets are called conglutinates.
When a predator fish tries to eat this decoy, the conglutinate ruptures in its
mouth, releasing the glochidia. |
Super Conglutinate!
|
The ultimate in mussel trickery is called a super
conglutinate! This is made up of dozens of conglutinates
formed into a larger shape that are attached to the mother mussel by a long mucous ribbon,
which allows it to wave back and forth in the water - just like a fishing lure on the end
of a line! The tightly packed rows of conglutinates bear an incredible resemblance
to the segmented appearance of some kinds of minnows. Any fish that chomps down on
one of these will REALLY get a dose of glochidia! This photo shows the super
conglutinate lure of Lampsilis perovalis, the Orange-Nacre
Mucket. It even has a lateral stripe and a "head"! You can see more
pictures of it on Dr. Chris Barnhart's web site listed in the links below, including a
video of it waving in the current! |
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| Mussels are filter feeders. They pump
water through themselves using two tubes called siphons.
As the water passes through the mussel, it gets oxygen and food. As the water
leaves, it carries away waste products and (in season) sperm and glochidia. The
siphons are located at the posterior end
of the shell, which is at the end opposite the pseudocardinal teeth. (The anterior end is the one
closest to the pseudocardinal teeth.) Mussels will always seek to orient themselves
with the posterior end sticking out of the substrate so they can use their siphons
properly. |
| Mussels may live over 100 years, although most live 20 to 30
years. Generally, the thinner-shelled species live shorter lives,
although they grow quicker. |
| Mussels are declining in North America. Of
the ~300 different species of mussels in North America, over 44% are either extinct
or in serious decline. In Kansas, the figure is 60%. No other class of animal
or plant is in as much trouble.
 | As with most types of wildlife, habitat loss is the main problem.
Channelization and gravel dredging disrupts or eliminates the bottom substrate
where the mussels live. Excessive siltation from soil erosion smothers them.
Altered flow regimes below dams de-stabilize the natural continuity of bottom
substrates. Withdrawl of water from rivers for irrigation and other purposes can
cause the rivers to go dry. Damming a river into a lake or reservoir limits the
number of mussel species that can survive there. |
| Water pollution harms mussels, although the impact is hard to
quantify. They can be poisoned outright - just as fish can - by large doses of
pollution. But there are probably more subtle impacts through disrupting the
reproductive cycle and killing off the fish hosts of their glochidia. |
| Overharvest for human use has contributed to their decline in some cases. Many
species of mussels were harvested heavily in the early 1900's. Their shells were
used to make buttons for clothing. This harvest was unregulated and many species of
mussels were severely impacted by it. This business ended after the 1940's due to
the invention of plastic buttons.
Commercial
harvesting began again around 1960. This time the thicker-shelled species were the
target. Their shells were cut up and used as nuclei for cultured pearls. This
market lasted through the mid-1990's. Most states attempt to regulate this harvest
through size and catch limits, but enforcement of the regulations is often difficult.
The market has fallen off in recent years in part due to the use of synthetic
nuclei.
In certain areas
mussels are overharvested by people hoping to find freshwater pearls. Few species of
mussel produce pearls and most of the pearls produced are of poor quality. In
addition, the incidence of freshwater pearls is very small even in those species that are
known to produce them (less than 4% at best). Consequently, vast numbers of mussels
are slaughtered for a very few pearls. Some attempts have been made to culture
freshwater pearls - with modest success - so hopefully this sustainable method will
replace the extremely wasteful and illegal wild harvest. |
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OTHER
FRESHWATER BIVALVES IN KANSAS
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Zebra mussel shells
Close-up view showing the stripes
- Photos by Jim Mason
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The zebra mussel
(Dreissenia polymorpha)
is NOT a unionid mussel. It is a dangerous new invasive species in North
America. While less than an inch in length, it has a tremendous reproductive rate
and apparently no significant natural enemies in North America. It's larvae are
free-swimming and do not require an intermediate host. They will attach to any hard
surface, even each other. Note the baby zebras that were growing on the adults in
the picture to the left. They are capable of completely obstructing water intakes at
power plants and can smother native mussels by growing all over them.Unfortunately,
zebra mussels were discovered in Kansas in El Dorado Lake in August 2003 and in Winfield
City Lake in December 2006. It is essential that anglers, boaters and anyone else
who engages in water sports in these lakes - or any other body of water that is infested
with zebra mussels - exercise the utmost care to keep them out of other watersheds.
See the Mussel Bed for more information on the
species in Kansas.
Click here
to learn more about them and how you can help prevent the spread of this unwanted invader.
Click
here for the Kansas Department of Wildlife and Parks web page on zebra mussels.
 Click the icon for the KDWP brochure on
zebra mussels. (307K pdf file)
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Fingernail Clams
(Family Sphaeriidae) are also NOT unionid mussels.
These are very small bivalves (<20 mm.) which are often found in streams.
They are related to the Asiatic Clam, and have the same arrangement of the shell
teeth.
About 20 species are known from Kansas. They are an important part of the aquatic
food chain. |
| The Asiatic Clam
(Corbicula fluminea) is also NOT a unionid mussel. This small (< 1.5
inches) bivalve is found throughout much of North America. While it does not pose
the same economic threat as the Zebra mussel, it does compete for food with our native
species. It is easily recognized by its triangular shape and by having lateral teeth
on both sides of its true cardinal teeth.
See the Mussel Bed for more information on the
species in Kansas. |
Full-grown Corbicula shells
photo by Jim Mason |
| MUSSEL RESEARCH:
IN KANSAS - An informal group made up of federal, state and local government
employees, academic researchers, representatives from conservation organizations, teachers
and private individuals meets once a year for a workshop on freshwater mussels. The
group publishes The Kansas Pearly Mussel Newsline. You can download back issues by
clicking on the icons below. The files are in pdf format, which requires Acrobat
Reader.
(On a Windows system, download the file by right clicking on the link and choose
"Save Target As" to save it to your hard drive, then open it from there.
You will need Acrobat Reader to view this file. If you don't have that software
already, you can get it for free from Adobe.)
| 1996 issue (163K) |
| 1997 issue (220K) |
| 1998 issue (114K) |
| 1999 issue (202K) |
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| 2000 issue (213K) |
| 2001 issue (530K) |
| 2002 issue (463K) |
| 2004 issue (212K)
(there was no 2003 issue) |
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LIST OF KANSAS MUSSELS:
There are 48 species of mussels recorded from Kansas. Click on the species name
in the list below to see detailed range maps, habitat and life history information for
each. The list is based on "A Pocket Guide to Freshwater Mussels", 2008,
Great Plains Nature Center, by Edwin Miller, Karen Couch & Jim Mason. It may be
picked up for free at the Great Plains Nature Center or ordered
through the mail for a nominal fee.
KANSAS STATUS
X = Species that are extirpated from Kansas (8).
!! = Species that are endangered
in Kansas (7).
! = Species that are
threatened in Kansas (4).
+ = Species that are in need of
conservation in Kansas (11).
NR= Species that are recently recorded and have not been
classified. (1)
Sub-Family Cumberlandinae
Genus Cumberlandia
X Spectaclecase - Cumberlandia monodonta
Sub-Family Ambleminae
Genus Megalonaias
+ Washboard - Megalonais nervosa
Genus Tritogonia
Pistolgrip - Tritogonia verrucosa
Genus Quadrula
X
Winged Mapleleaf - Quadrula fragosa
Mapleleaf
- Quadrula quadrula
Pimpleback
- Quadrula pustulosa
+ Wartyback - Quadrula nodulata
Monkeyface
- Quadrula metanevra
!! Rabbitsfoot - Quadrula cylindrica
Genus Amblema
Threeridge - Amblema plicata
Genus Fusconaia
+ Wabash
Pigtoe - Fusconaia flava
Genus Cyclonaias
NR Purple Wartyback - Cyclonaias
tuberculata
Genus Pleurobema
X Pyramid Pigtoe - Pleurobema rubrum
+ Round Pigtoe - Pleurobema sintoxia
Genus Elliptio
+ Spike - Elliptio dilatata
Genus Uniomerus
Pondhorn - Uniomerus tetralasmus
Sub-Family Anodontinae
Genus Utterbackia
Paper Pondshell - Utterbackia imbecillis
Genus Anodonta
!! Flat Floater - Anodonta suborbiculata
Genus Pyganodon
Floater - Pyganodon grandis
Genus Anodontoides
+ Cylindrical Papershell - Anodontoides
ferussacianus
Genus Strophitus
+ Creeper - Strophitus undulatus
Genus Alasmidonta
!! Elktoe - Alasmidonta marginata
X Slippershell - Alasmidonta
viridis
Genus Arcidens
! Rock Pocketbook - Arcidens
confragosus
Genus Lasmigona
X Creek Heelsplitter - Lasmigona compressa
! Flutedshell - Lasmigona
costata
White
Heelsplitter - Lasmigona complanata
Sub-Family Lampsilinae
Genus Ptychobranchus
! Ouachita Kidneyshell
- Ptychobranchus occidentalis
Genus Obliquaria
Threehorn
Wartyback - Obliquaria reflexa
Genus Cyprogenia
!! Western Fanshell - Cyprogenia aberti
Genus Actinonaias
!! Mucket - Actinonaias ligamentina
Genus Ellipsaria
! Butterfly - Ellipsaria
lineolata
Genus Obovaria
X Hickorynut - Obovaria
olivaria
Genus Truncilla
+ Deertoe - Truncilla truncata
+ Fawnsfoot - Truncilla donaciformis
Genus Leptodea
Fragile
Papershell - Leptodea fragilis
Genus Potamilus
Pink
Papershell - Potamilus ohiensis
Pink
Heelsplitter - Potamilus alatus
Bleufer
- Potamilus purpuratus
Genus Toxolasma
Lilliput
- Toxolasma parvus
Genus Ligumia
X Black Sandshell - Ligumia recta
Pondmussel
- Ligumia subrostrata
Genus Venustaconcha
!! Ellipse- Venustaconcha ellipsiformis
Genus Lampsilis
+ Yellow Sandshell - Lampsilis teres
+ Fatmucket - Lampsilis siliquoidea
!! Neosho Mucket - Lampsilis rafinesqueana
Plain Pocketbook - Lampsilis cardium
Genus Epioblasma
X Snuffbox - Epioblasma
triquetra
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