Aspidogaster conchicola

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)

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)

  • 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)

  • 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)

  • 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)

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

Con­trib­u­tors

Renee Sher­man Mul­crone (ed­i­tor).

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

Glossary

Ethiopian

living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.

World Map

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Palearctic

living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

ectothermic

animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature

fertilization

union of egg and spermatozoan

freshwater

mainly lives in water that is not salty.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

internal fertilization

fertilization takes place within the female's body

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

parasite

an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

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.