Animal Diversity Web

Ge­o­graphic Range

The range for Fus­conaia ebena, or ebonyshells, is the Mis­sis­sippi River basin, in­clud­ing the Mis­sis­sippi River, the Min­nesota River, the St. Croix River, the Illi­nois River, the Ohio River, and other bod­ies of water in the basin that offer suit­able liv­ing con­di­tions for this mus­sel. Orig­i­nally, the na­tive range ex­tended from around the Twin Cities in Min­nesota and went all the way to the Gulf of Mex­ico. In 1913, a dam was built on the Mis­sis­sippi River in Keokuk, Iowa, ef­fec­tively cut­ting off the north­ern home range for breed­ing ebonyshells. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Cum­mings and Mayer, 1992; Illi­nois State Mu­seum, et al., 2011; Wis­con­sin Dept. of Nat­ural Re­sources, 2009)

• Biogeographic Regions
• nearctic
  • native

Habi­tat

The pre­ferred habi­tat of ebonyshells is in deep (6 ft/1.8 m), strong cur­rents of large rivers, but they can be found in deeper or shal­lower wa­ters with weaker cur­rents. Ebonyshells are found in areas with rocks, gravel, or sand on the bot­toms of these rivers and will some­times bur­row down un­der­neath the sand or mud. (Wis­con­sin Dept. of Nat­ural Re­sources, 2009)

• Habitat Regions
• temperate
• freshwater

• Aquatic Biomes
• rivers and streams

• Other Habitat Features
• riparian

• Average depth

  1.8 m

  5.91 ft

Phys­i­cal De­scrip­tion

Ebonyshells can be char­ac­ter­ized pri­mar­ily by their size, shape, and color pat­terns. Adults are typ­i­cally 7.4 cm in length but can grow up to 10.2 cm or more. They are cir­cu­lar, round or sub-el­lip­ti­cal. Their shell is thick and in­flated with a pro­nounced beak which fits in with over­all round­ness. Their shell is smooth and lacks pus­tules. The dark color of ma­ture adults is what gives ebonyshells their name. As ma­ture adults, the ex­te­rior of the shell dis­plays con­cen­tric bands that em­i­nate from their beak. The color of these bands ranges from light and dark brown to black. As ju­ve­niles, these bands are more yel­low, with bright green and brown bands. A dis­tin­guish­ing fea­ture of ebonyshells is that there are no rays (per­pen­dic­u­lar to the bands) on the shell. On the inner sur­face of the shell, they are pearly white and glossy, and bands are ab­sent. They have four well de­vel­oped pseudo­car­di­nal teeth (two in both the right and left valve), and three lat­eral teeth that are ser­rated and curved (two in the left valve and one in the right valve). (Cum­mings and Mayer, 1992; Illi­nois State Mu­seum, et al., 2011; Wis­con­sin Dept. of Nat­ural Re­sources, 2009)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• Sexual Dimorphism
• sexes alike

• Range length

  10.2 (high) cm

  4.02 (high) in

• Average length

  7.4 cm

  2.91 in

De­vel­op­ment

After the ebonyshell eggs are fer­til­ized, they de­velop into lar­vae (called glochidia) in the fe­male's gills. Then, the lar­vae are re­leased into the water to at­tach to a host fish. After the glochidia de­velop to ju­ve­niles, they de­tach from the host fish and drift in the water until set­tling at the river bot­tom. Here they will stay and con­tinue to grow and re­peat the cycle. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011)

Their pri­mary host fish are skip­jack her­ring (Alosa chrysochlo­ris) which are mi­gra­tory fish. Other sus­pected host species in­clude black crap­pie (Po­moxis ni­gro­mac­u­la­tus), white crap­pie (Po­moxis an­nu­laris), and large­mouth bass (Mi­cropterus salmoides). The glochidia are pack­aged to­gether to be trans­ferred from fe­male ebonyshells to skip­jack her­ring or other host fish, cre­at­ing a lure which at­tracts the fish. This lure is re­leased into the water when the fish come close to the fe­male ebonyshells. When the glochidial packet is re­leased, it drifts up in the cur­rent, look­ing like a worm. The fish tear open and eat the glochidial packet, free­ing the bi­valved lar­vae that are fil­tered out through the gills as the fish breathes. The lar­vae at­tach to the gills or to an ex­te­rior sur­face of the fish, and the fish tis­sue forms a pro­tec­tive cyst around glochidia. The cyst is very small, and does not ef­fect the host fish. The glochidia de­velop into ju­ve­niles while at­tached to the fish. After meta­mor­phos­ing to ju­ve­niles, each glochid­ium is sloughed off and the ju­ve­nile be­comes a free liv­ing or­gan­ism. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Min­nesota Dept of Nat­ural Re­sources, 2011; Wis­con­sin Dept. of Nat­ural Re­sources, 2009)

Once ju­ve­niles are free of the host fish, they even­tu­ally rest on the river bot­tom. They con­tinue to grow dur­ing the warmer months of the year, adding shell ma­te­r­ial until the fol­low­ing win­ter. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Wis­con­sin Dept. of Nat­ural Re­sources, 2009)

• Development - Life Cycle
• metamorphosis

Re­pro­duc­tion

Fresh­wa­ter unionid mus­sels typ­i­cally live within close prox­im­ity to one an­other on the river bot­tom, re­ferred to as beds. While there is no known sig­nal or other type of com­mu­ni­ca­tion be­tween males and fe­males, males re­lease sperm into the water and the eggs are fer­til­ized as fe­males siphons in sperm as it siphons for food. The eggs are brooded in the gills of the fe­male ebonyshells. Sperm that do not fer­tilze eggs quickly die off and drift down river. Be­cause of this ran­dom ejec­tion of sperm, it is not pos­si­ble to know how many males or fe­males are mat­ing with each other. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Min­nesota Dept of Nat­ural Re­sources, 2011)

• Mating System
• polygynandrous (promiscuous)

The breed­ing sea­son of ebonyshells is from June until Sep­tem­ber. A sin­gle fe­male ebonyshell is ca­pa­ble of pro­duc­ing and fer­til­iz­ing tens of thou­sands of eggs each year. Once the eggs have hatched into lar­vae, they are passed on to the host fish where they con­tinue to grow into ju­ve­niles. The time of de­vel­op­ment from larva to ju­ve­nile on the host fish, can take any­where from a few days to a cou­ple months. (Min­nesota Dept of Nat­ural Re­sources, 2011; Wis­con­sin Dept. of Nat­ural Re­sources, 2009)

• Key Reproductive Features
• seasonal breeding
• sexual
• fertilization
  • internal
• ovoviviparous

• Breeding interval

  Ebonyshells spawn once every year.

• Breeding season

  Ebonyshells breed from June to September.

• Range number of offspring

  1000 to 50,000

• Average number of offspring

  10,000

• Range time to independence

  1 to 8 weeks

• Average time to independence

  4 weeks

Parental in­vest­ment is very min­i­mal in ebonyshells and in other mus­sels. The main in­vest­ment of ei­ther par­ent is to pro­duce ga­metes. The fe­male broods the fer­til­ized eggs until they hatch into lar­vae. After re­lease of the eggs, all as­so­ci­a­tion to the par­ent is gone. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Min­nesota Dept of Nat­ural Re­sources, 2011)

• Parental Investment
• pre-fertilization
  • provisioning
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifes­pan/Longevity

The age of ebonyshells can be de­ter­mined by ex­am­in­ing the num­ber con­cen­tric rings on the ex­te­rior of the shell (sim­i­lar to aging a tree). The old­est ebonyshells found have been well over 100 years old, but the typ­i­cal lifes­pan for this species is 10 to 40 years. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Min­nesota Dept of Nat­ural Re­sources, 2011)

• Range lifespan
  Status: wild

  100 (high) years

• Average lifespan
  Status: wild

  75 years

• Typical lifespan
  Status: wild

  10 to 40 years

Be­hav­ior

Ebonyshells are mostly soli­tary species. They may live in close prox­im­ity to other ebonyshells but do not in­ter­act with each other. One of the only ob­served so­cial in­ter­ac­tions is the lur­ing of the host fish by the fe­male. When en­coun­tered by a preda­tor, ebonyshells seal them­selves shut, try to bur­row into the muck, or shoot jets of water ei­ther for propul­sion or to dis­tract the preda­tor. Ebonyshells move around by drift­ing in the cur­rent, water jet propul­sion, or by using their pseudo­pod (foot). ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Min­nesota Dept of Nat­ural Re­sources, 2011)

• Key Behaviors
• motile
• sedentary

Home Range

The home range for ebonyshells is un­known. Adult mus­sels move only a few me­ters from where they set­tle as ju­ve­niles.

Com­mu­ni­ca­tion and Per­cep­tion

Com­mu­ni­ca­tion in not ob­served in ebonyshells ex­cept in the lur­ing of the host fish and re­act­ing to touch (most likely from a preda­tor). ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011)

• Communication Channels
• tactile
• chemical

• Perception Channels
• tactile
• chemical

Food Habits

Ebonyshells are fil­ter feed­ers. First, they siphon water and the gills fil­ter for food. Then, cilia draws the food out of gills and into the di­ges­tive sys­tem. Foods known to be ex­tracted from this fil­ter­ing in­cludes: algae, plank­ton, small aquatic in­ver­te­brates (in­sects and worms), de­tri­tus, and de­cay­ing or­ganic ma­te­r­ial. (Cum­mings and Mayer, 1992; Min­nesota Dept of Nat­ural Re­sources, 2011)

• Primary Diet
• herbivore
  • algivore
• omnivore
• planktivore
• detritivore

• Plant Foods
• algae
• phytoplankton

• Other Foods
• detritus
• microbes

• Foraging Behavior
• filter-feeding

Pre­da­tion

Com­mon preda­tors of mus­sels in­clude rac­coons (Pro­cyon lotor), river ot­ters (Lon­tra canaden­sis), muskrats (On­do­tra zi­bethi­cus), herons and egrets (Ardeinae), and some larger fish (Actinoptery­gii). To com­bat pre­da­tion, ebonyshells darkly col­ored on the out­side of their shells to pro­vide cam­ou­flage. Also, they have a hard thick shell and strong ad­duc­tors (which pull and keep the shell closed) that help in pro­tect­ing them­selves from preda­tors. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Min­nesota Dept of Nat­ural Re­sources, 2011)

• Anti-predator Adaptations
• cryptic

• Known Predators

  • raccoons (Procyon lotor)
  • river otters (Lontra canadensis)
  • muskrats (Ondotra zibethicus)
  • herons and egrets (Ardeinae)
  • larger fish (Actinopterygii)

Ecosys­tem Roles

Be­sides their role in the food web, ebonyshells play an im­por­tant role in the ecosys­tem. One thing that ebonyshells do is im­prove the qual­ity of the water by fil­ter­ing it. Their pres­ence in the water is also good sign of water qual­ity for use by other an­i­mals, like fish and birds. Their lar­vae use Skip­jack her­rings (Alosa chrysochlo­ris), black crap­pies (Pox­omis ni­gro­mac­u­la­tus), white crap­pies (Po­moxis an­nu­laris), and large­mouth bass (Mi­cropteris salmoides) as hosts dur­ing their de­vel­op­ment. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

When set­tlers were com­ing into the Mis­sis­sippi River area, ebonyshells are har­vested in great quan­ti­ties for their shells (thick and high in qual­ity) which were used in the pearl but­ton in­dus­try. This mass har­vest pushed the species close to ex­tinc­tion in some areas. They were also once har­vested for food, but they taste rather bit­ter and now ma­rine mus­sels, clams and oys­ters are avail­able which taste bet­ter. Today, mus­sels are still har­vested pri­mar­ily to be ex­ported and then used in cul­tured pearl farms (some of which are in Japan). Mus­sels are valu­able in sci­en­tific and med­ical re­search be­cause mus­sels can­not get can­cer, and the rea­son for this is un­known. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Wis­con­sin Dept. of Nat­ural Re­sources, 2009)

Mus­sels are good in­di­ca­tors of water qual­ity, and they also help to im­prove the qual­ity of water by fil­tra­tion. Pres­ence of ebonyshells is also a good in­di­ca­tor for the health of the dif­fer­ent host species, be­cause they can­not live in an area ab­sent of their host fish. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Wis­con­sin Dept. of Nat­ural Re­sources, 2009)

Peo­ple are now tak­ing more ac­tion to help ebonyshells by en­forc­ing habi­tat pro­tec­tion, dredg­ing re­stric­tions, im­pound­ment re­stric­tions, sand and gravel min­ing re­stric­tions, and by de­vel­op­ing of path­ways (fish run­aways) for host species to mi­grate unim­peded up river (by­pass­ing the locks and dams). ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Wis­con­sin Dept. of Nat­ural Re­sources, 2009)

• Positive Impacts
• body parts are source of valuable material
• research and education

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

There are no known ad­verse ef­fects of ebonyshells on hu­mans.

Con­ser­va­tion Sta­tus

There is no fed­eral or na­tional sta­tus rank­ing pro­vided for ebonyshells. How­ever, they are on some con­ser­va­tion lists in some states. They are en­dan­gered in Wis­con­sin and Mis­souri, threat­ened in Illi­nois and Ohio, and con­sid­ered spe­cial in­ter­est in Illi­nois and Min­nesota. ("United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels", 2011; Cum­mings and Mayer, 1992; Illi­nois State Mu­seum, et al., 2011; Min­nesota Dept of Nat­ural Re­sources, 2011; Wis­con­sin Dept. of Nat­ural Re­sources, 2009)

• IUCN Red List

  Not Evaluated

• US Federal List

  No special status

• CITES

  No special status

• State of Michigan List

  No special status

Con­trib­u­tors

Ryan Bohn (au­thor), Min­nesota State Uni­ver­sity, Mankato, Robert Sorensen (ed­i­tor), Min­nesota State Uni­ver­sity, Mankato, Renee Mul­crone (ed­i­tor), Spe­cial Pro­jects, Cather­ine Kent (ed­i­tor), Spe­cial Pro­jects.

Ref­er­ences

United States Fish and Wildlife Ser­vice. United States Fish and Wildlife Ser­vice: En­dan­gered Species: Amer­ica's Mus­sels: Silent Sen­tinels. Un­known. On­line: United States Fish and Wildlife Ser­vice. 2011. Ac­cessed April 30, 2011 at http://​www.​fws.​gov/​midwest/​endangered/​clams/​mussels.​html.

Cum­mings, K., C. Mayer. 1992. "Fus­conaia ebena" (On-line). Field guide to fresh­wa­ter mus­sels of the Mid­west. Illi­nois Nat­ural His­tory Sur­vey Man­ual 5. Ac­cessed July 21, 2011 at http://​www.​inhs.​illinois.​edu/​animals_​plants/​mollusk/​musselmanual/​page42_​3.​html.

Illi­nois State Mu­seum, , Ha­vana Pub­lic Li­brary Dis­trict, Mere­dosia River Mu­seum. 2011. "Ebony Shell" (On-line). Har­vest­ing the River. Ac­cessed July 11, 2011 at http://​www.​museum.​state.​il.​us/​RiverWeb/​harvesting/​harvest/​mussels/​species/​ebonyshell.​html.

Min­nesota Dept of Nat­ural Re­sources, 2011. "Fus­conaia ebena (I. Lea, 1831)" (On-line). Min­nesota Dept. of Nat­ural Re­sources Rare Species Guide. Ac­cessed July 21, 2011 at http://​www.​dnr.​state.​mn.​us/​rsg/​profile.​html?​action=elementDetail&​selectedElement=IMBIV17060.

Wis­con­sin Dept. of Nat­ural Re­sources, 2009. "Ebony Shell (Fus­conaia ebena)" (On-line). En­dan­gered Re­sources Pro­gram Species In­for­ma­tion. Ac­cessed July 07, 2011 at http://​dnr.​wi.​gov/​org/​land/​er/​biodiversity/​index.​asp?​mode=info&​Grp=19&​SpecCode=IMBIV17060.