Animal Diversity Web

Ge­o­graphic Range

As­pi­do­gaster conchicola is a par­a­site of fresh­wa­ter bi­valves, with a wide dis­tri­b­u­tion in North Amer­ica, Africa, and Eu­rope. This small fluke has a low de­gree of host speci­ficity and has been found in a wide va­ri­ety of other hosts, in­clud­ing snails, fish, and tur­tles. In­side the typ­i­cal mol­lus­can host, the par­a­site will usu­ally take res­i­dence within the peri­car­dial cav­ity. (Huehner and Etges, 1977; Rohde, 1972)

• Biogeographic Regions
• nearctic
  • native
• palearctic
  • native
• ethiopian
  • native

Habi­tat

Not being well adapted to any sin­gle host species, A. conchicola will read­ily de­velop in a wide va­ri­ety of fresh­wa­ter mol­lusk, snail, fish, or tur­tle fam­i­lies. In lab­o­ra­tory set­tings A. conchicola was able to sur­vive in water for two weeks with­out a host, and in a saline so­lu­tion for up to five weeks. This sug­gests that As­pi­do­gaster is an ar­chaic species, not too far re­moved from a free-liv­ing an­ces­tor. (Rohde, 1972; Rohde, 1998)

• Habitat Regions
• freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams

Phys­i­cal De­scrip­tion

The ma­ture As­pi­do­gaster conchicola is ap­prox­i­mately 2.5 to 3.0 mm in length and 1.0 mm wide, and some­what re­sem­bles a minia­ture conch. A sin­gle large ven­tral sucker, known as an opisthap­tor, takes up most of the sur­face area of its un­der­belly. The opisthap­tor is di­vided into ad­he­sive de­pres­sions (termed lo­culi) formed by mus­cu­lar septa, which are use­ful in clas­si­fi­ca­tion. As­pi­do­gaster conchicola has 64-66 lo­culi, arranged in four lon­gi­tu­di­nal rows. An ex­te­rior lon­gi­tu­di­nal sep­tum, which is a hor­i­zon­tal flap of mus­cle, di­vides the body an­te­ri­orly. The func­tion of the sep­tum is un­known.

A wide buc­cal fun­nel (mouth) has its open­ing at the an­te­rior end of a flex­i­ble neck-like process. Pha­ryn­geal mus­cles move food en­ter­ing the buc­cal fun­nel into the in­tes­tine. Un­like the re­lated Di­ge­nean worms, as­pi­doboth­re­ans have a sim­ple, un­branched di­ges­tive tract that ends in the cecum, a di­ges­tive sac sur­rounded by mus­cle. Wastes are re­moved by flame cell pro­tonephridia, which chan­nel ma­te­r­ial through ex­cre­tory ducts into an ex­cre­tory blad­der, even­tu­ally ex­it­ing the body through a pos­te­ri­orly lo­cated ex­cre­tory pore.

An in­ter­est­ing fea­ture of A. conchicola is its com­plex ner­vous sys­tem, a fea­ture more char­ac­ter­is­tic of free-liv­ing rather than par­a­sitic worms. As­pi­do­gaster conchicola pos­sesses an an­te­rior cere­bral com­mis­sure, an in­tri­cate or­ga­ni­za­tion of nerves. This pre­sum­ably serves to co­or­di­nate the pe­riph­eral nerves, which are arranged in a lad­der-type sys­tem. Nu­mer­ous types of sen­sory re­cep­tors have been ob­served, par­tic­u­larly con­cen­trated around the buc­cal fun­nel and opisthap­tor, in­di­cat­ing that there is a good de­gree of neural co­or­di­na­tion of lo­co­mo­tive and di­ges­tive ac­tion. (Bai­ley and Tomp­kin, 1971; Hal­ton and Ly­ness, 1971; Hath­away, 1971; Roberts and Janovy Jr., 2000)

• Other Physical Features
• ectothermic
• heterothermic
• bilateral symmetry

• Average length

  2.5 to 3 mm

  in

Re­pro­duc­tion

As­pi­do­gaster conchicola usu­ally de­vel­ops within mol­lusks, but is a fac­ul­ta­tive par­a­site of ver­te­brates, should their mol­lusk host be eaten. Their life cycle is still di­rect, re­quir­ing only one host for mat­u­ra­tion. In­fec­tion oc­curs through in­take of the egg, con­tain­ing a fully de­vel­oped larva, by the mol­lusk's siphon. Upon en­ter­ing the host, the coty­locid­ium (lar­vae) will hatch and im­me­di­ately begin mat­u­ra­tion with­out fur­ther mi­gra­tion. At hatch­ing, the lar­vae are 13 to 17 mi­crom­e­ters long. Since the coty­locid­ium does not seek the host as in other trema­todes, it is un­cil­i­ated. In­stead, it has a sim­ple pos­te­rior sucker lack­ing lo­culi. There have been no doc­u­mented cases of As­pi­do­gaster di­rectly in­fect­ing a ver­te­brate host as a free egg or larva, while they have been found in the in­testines of fish, so it is as­sumed that ver­te­brates are in­fected by in­ges­tion of par­a­sitized mol­lusks.

As­pi­doboth­re­ans are able to ei­ther self-fer­til­ize or mate with an­other in­di­vid­ual. (Bakker and Davids, 1973; Huehner and Etges, 1977; Rohde, 1972; Rohde, 1998)

• Key Reproductive Features
• simultaneous hermaphrodite
• sexual
• fertilization
  • internal
• ovoviviparous
• oviparous

• Parental Investment
• no parental involvement

Be­hav­ior

The large ven­tral opisthap­tor ap­pears to play a major role in As­pi­do­gaster conchicola feed­ing be­hav­ior. Mus­cu­lar ac­tion me­chan­i­cally dis­rupts host tis­sues while mar­ginal or­gans within the sucker re­lease se­cre­tions for ex­tra­cor­po­real di­ges­tion. The predi­gested ma­te­r­ial is then sucked in through the buc­cal fun­nel.

As­pi­do­gaster in­fec­tions ap­pear to be most preva­lent and in­tense dur­ing the colder months, from No­vem­ber through April. (Bai­ley and Tomp­kin, 1971; Hal­ton and Ly­ness, 1971; Huehner, 1987; Huehner, et al., 1989)

• Key Behaviors
• parasite

Food Habits

The pri­mary hosts for As­pi­do­gaster conchicola are fresh­wa­ter mol­lusks, usu­ally mus­sels. How­ever, as a fac­ul­ta­tive par­a­site of ver­te­brates, it is not re­stricted to mus­sels, and will also enter into and de­velop within fresh­wa­ter snails, fishes, and tur­tles while feed­ing on ep­ithe­lial tis­sue. (Rohde, 1972)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

The as­pi­doboth­re­ans do not hold any eco­nomic or med­ical sig­nif­i­cance for hu­mans. How­ever, they have sev­eral ar­chaic char­ac­ter­is­tics which sug­gest that they are an an­cient group, and so con­tinue to be stud­ied be­cause they seem to rep­re­sent a link be­tween par­a­sitic and free-liv­ing or­gan­isms. Since As­pi­do­gaster has not de­vel­oped any close as­so­ci­a­tions with par­tic­u­lar host species, it has been sug­gested that it is an ar­chaic species of trema­tode, sim­i­lar to the hy­po­thet­i­cal an­ces­tor from which the re­lated di­ge­nean trema­todes have evolved their com­plex life cy­cles ex­ploit­ing mul­ti­ple hosts. (Rohde, 1972)

As­pi­do­gaster conchicola in­fects the zebra mus­sel, Dreis­sena poly­mor­pha, which is an in­va­sive species in the Great Lakes in the United States. (Laru­elle and Mol­logy, 1996)

Con­ser­va­tion Sta­tus

• IUCN Red List

  No special status

• US Federal List

  No special status

• CITES

  No special status

Con­trib­u­tors

Renee Sher­man Mul­crone (ed­i­tor).

Ray­mond Pahk (au­thor), Uni­ver­sity of Michi­gan-Ann Arbor, Solomon David (ed­i­tor), Uni­ver­sity of Michi­gan-Ann Arbor.

Ref­er­ences

Uni­ver­sity of Man­i­toba. 2000. "Coty­lo­gaster oc­ci­den­talis" (On-line). WEL­COME TO PAR­A­SITOL­OGY 22.346. Ac­cessed No­vem­ber 14, 2003 at http://​www.​umanitoba.​ca/​faculties/​science/​zoology/​faculty/​dick/​z346/​aspidohome.​html.

Bai­ley, H., S. Tomp­kin. 1971. Ul­tra­struc­ture of the in­tegu­ment of As­pi­do­gaster conchicola. Jour­nal of Par­a­sitol­ogy, 57: 848-854.

Bakker, K., C. Davids. 1973. Notes on the life his­tory of As­pi­do­gaster conchicola Baer (Trema­toda; As­pi­do­gastri­dae). Jour­nal of Helminthol­ogy, 47: 269-276.

Hal­ton, D., R. Ly­ness. 1971. Ul­tra­struc­ture of the tegu­ment and as­so­ci­ated struc­tures of As­pi­do­gaster conchicola (Trema­toda; As­pi­do­gas­trea). Jour­nal of Par­a­sitol­ogy, 57: 1198-1210.

Hath­away, R. 1971. The fine struc­ture of the trema­tode As­pi­do­gaster conchicola von Baer, 1827. Dis­ser­ta­tion Ab­stracts In­ter­na­tional, 31B: 7687.

Huehner, M. 1987. As­pi­do­gastrid and di­ge­netic trema­tode sin­gle an dou­ble in­fec­tions in the gas­tro­pod Elimia livescens from the Upper Cuya­hoga River, Ohio USA. Pro­ceed­ings of the Helmintho­log­i­cal So­ci­ety of Wash­ing­ton, 54 (2): 200-203.

Huehner, M., F. Etges. 1977. The life cycle and de­vel­op­ment of As­pi­do­gaster conchicola in the snails, Vi­vip­a­rus mal­lea­tus and Go­nioba­sis livescens. Jour­nal of Par­a­sitol­ogy, 63: 669-674.

Huehner, M., K. Han­nan, M. Garvin. 1989. Feed­ing habits and mar­ginal organ his­to­chem­istry of As­pi­do­gaster conchicola (Trema­toda; As­pi­do­gas­trea). Jour­nal of Par­a­sitol­ogy, 75 (6): 848-852.

Laru­elle, F., D. Mol­logy. 1996. A Guide to Iden­ti­fy­ing the En­dosym­bionts of Dreis­sena poly­mor­pha. The 6th In­ter­na­tional Zebra Mus­sel and Other Aquatic Nui­sance Species Con­fer­ence, Dear­born, Michi­gan. Ac­cessed No­vem­ber 14, 2003 at http://​sgnis.​org/​publicat/​96Laruel.​htm.

Roberts, L., J. Janovy Jr.. 2000. Foun­da­tions of Par­a­sitol­ogy, 6th ed. New York: Mc­Graw Hill.

Rohde, K. 1998. "As­pi­do­gas­trea" (On-line). Ac­cessed 11/14/03 at http://​ag.​arizona.​edu/​ENTO/​tree/​eukaryotes/​animals/​platyhelminthes/​aspidogastrea/​aspidogastrea.​html.

Rohde, K. 1972. The As­pi­do­gas­trea, es­pe­cially Mul­ti­cotyle purvisi Dawes, 1941. Ad­vances in Par­a­sitol­ogy, 10: 77-151.