US Federal List: no special status
CITES: no special status
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.
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.
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.
Biogeographic Regions: nearctic (Native ); palearctic (Native ); ethiopian (Native )
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
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.
Average length: 2.5 to 3 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry
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 (Internal ); ovoviviparous ; oviparous
Parental Investment: no parental involvement
Aspidogaster conchicola is a trematode parasite of the Aspidogastrea subclass that commonly infects freshwater clams. It has not been well studied since it is of little economic or medical importance, but A. conchicola and its fellow aspidogastreans are of significant biological importance since they may represent a step between free-living and parasitic organisms.[3]
A. conchicola has a large ventral opisthaptor that extends most of its body's length, which is divided into sections called alveoli or loculi. It also possesses a longitudinal septum, a horizontal layer of muscle and connective tissue that separates the dorsal and ventral compartments of the body. The tegument is similar to that of other parasitic flatworms.
Aspidogaster conchicola infects many species of freshwater bivalves belonging to several families, as well as freshwater snails, many species of freshwater fishes of several families, and freshwater tortoises.[4]
Hosts include: Sinanodonta woodiana.[5]
Aspidogaster conchicola is a trematode parasite of the Aspidogastrea subclass that commonly infects freshwater clams. It has not been well studied since it is of little economic or medical importance, but A. conchicola and its fellow aspidogastreans are of significant biological importance since they may represent a step between free-living and parasitic organisms.
