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.
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.
- 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.
- Other Physical Features
- ectothermic
- heterothermic
- bilateral symmetry
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.
- Key Reproductive Features
- simultaneous hermaphrodite
- sexual
- fertilization
- 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.
- 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.
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.
Aspidogaster conchicola
infects the zebra mussel,
Dreissena polymorpha
, which is an invasive species in the Great Lakes in the United States.
Conservation Status
Additional Links
Contributors
Renee Sherman Mulcrone (editor).
Raymond Pahk (author), University of Michigan-Ann Arbor, Solomon David (editor), University of Michigan-Ann Arbor.
- 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.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Palearctic
-
living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- Ethiopian
-
living in sub-Saharan Africa (south of 30 degrees north) and Madagascar.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- freshwater
-
mainly lives in water that is not salty.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
- 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.
- 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.
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- fertilization
-
union of egg and spermatozoan
- internal fertilization
-
fertilization takes place within the female'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.
- oviparous
-
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
- parasite
-
an organism that obtains nutrients from other organisms in a harmful way that doesn't cause immediate death
References
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., 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.
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.
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.
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 .