Aquatic Parasite Observatory

Bucephalus elegans (Woodhead, 1930)

    • Species Name: Bucephalus elegans (Woodhead, I930)
    • Synonyms: None
    • Taxonomy: (Woodhead, 1930) Animalia, Platyhelminthes, Trematoda, Plagiorchiida, Bucephalidae, Bucephalus elegans
    • Description: Adult stage as described by Woodhead, 1930: The form of the body, in relaxed condition, is cylindrical, rounded posteriorly, truncate anteriorly. The terminal anterior surface is flat or slightly convex, depending upon the state of contraction of the head appendages. A large notch on the ventral margin of the anterior surface is observed in relaxed individuals. The head appendages seven in number, are located on the margin of the anterior surface. These head appendages, in the nature of fimbriae, appear first as short stalks with knob-like ends (Fig. 17). Later a small distal and a larger proximal protuberance appear on the underside of the fimbriae near its base. Complete extension then produces long, semi-rigid, downward-curving fimbriae with two finger-like processes near the base of each, the proximal process appearing twice as long as the distal. My observations on living specimens of B. elegans revealed the presence of a central cavity extending the length of the extended fimbriae and occupying about one-third of its diameter. Wagener (1858) in a figure of an "old specimen" of G. fimbriatum v. Siebold 1848, showed five partly extended fimbriae. Among the many older individuals of B. elegans which I have examined, only one living specimen showed the fimbriae completely extended. Diesing (1858) in a systematic paper created a new genus Gasterostomum on the basis of the complex and peculiar structure of the anterior end of G. fimbriatum as de-scribed by Wagener (1857). Ziegler (1883:549) pointed out what he considered the error in Wagener's interpretation of the anterior end of G. fimbriatum and was of the opinion that the "fimbriae" were caused by the contraction of the radial fibers of the anterior sucker. The large spheroidal anterior sucker extends from the ventral surface nearly to the dorsal surface, occupying most of the space at the anterior end of the body. It is composed of a mass of unicellular glands and radial muscle fibers, enclosed in a basement membrane. These muscle fibers are arranged in fourteen longitudinal layers which extend from the dorsal to the ventral wall of the sucker. The gland cells are located in the central region of the sucker, arranged in seven areas each area bounded on either side by one of the layers of muscle fibers. The layers of muscle fibers between adjacent glandular areas are separated by a thin layer of parenchyma. The gland cells, of two distinct sizes, pour their secretions into a pair of ventrally located ducts which lead to the anterior surface of the body. The larger cells, fewer in number, are located in the areas between the muscle fibers and are connected with the ducts by short secondary tubules. The smaller, more numerous cells are sessile on the ducts. Large spaces, surrounded by parenchyma, are located in each of the seven areas between the muscle fibers and dorsad to the glands. These dorsal spaces are associated with the seven extensible fimbriae. The basement membrane, of the anterior sucker, enters into the formation of the extensible fimbriae. When muscle fibers within the sucker contract, thus reducing the size of the spaces lying between them, a liquid within the spaces is forced against certain places on the anterior portion of the basement membrane which is forced outward from the body along with the cuticle and subcuticular muscle layers. This part of the sucker which is forced outward assumes a definite form, the fimbriae. Ziegler (1883) in a cross-section of the anterior region of G. fimbriatum, indicated six groups of these muscle fibers which by their contractions, he thought, caused the parenchyma cells and the muscle layers of the body wall between each group to be extended into a peg-shaped projection. My observations therefore tend to confirm Ziegler's conclusions as to the manner of formation of the fimbriae. The body is covered with a thin cuticle in which are embedded flat, blunt-pointed posteriad directed spines inserted acutely on a transversely elongate basal plate. The spines are more prominent in the anterior region and cover the entire lining of the anterior sucker, indicating that the sucker is formed as a depression on the ventral surface. Elongated subcuticular unicellular glands are uniformly distributed over the surface of the body be-neath the cuticle and body-wall muscles. Each cell is provided with a short duct leading to the surface, or joined to other short ducts and thence to the surface. Very little is known concerning the function of these glands. I hazard the suggestion that they may secrete a substance, perhaps mucus, that serves to protect the parasite from harmful substances, comparable to the function of mucus secreted by a fish or frog. The gut of B. elegans is more nearly oval than in B. papillosus previously described (Woodhead, 1929) and is relatively larger, measuring 0.112 to 0.160 mm. in length. The rest of the anatomy of the adult B. elegans is so similar to B. papillosus that further description is unnecessary. B. elegans has the largest egg of the three species of gasterostome thus far investigated. Eggs of older individuals were fewer in number and larger than eggs of younger specimens. A mature worm secured from an experimentally infected blue-gill, Lepomis pallidus, contained only 150 eggs. All were of a very uniform size and none were malformed. Discharged eggs of this individual measured 0.046 to 0.048 mm. by about 0.021 mm. The number of eggs in other individuals ranged from 50 to 250, the usual number being in the neighborhood of 200. Measurements of over 100 discharged eggs from different individuals showed a length of 0.040-0.050 mm., average 0.047 mm., and a width of 0.018 to 0.022 mm., average 0.021 mm.
    • Life Cycle: “Adult worms containing up to 200 eggs in various stages of development occur in the cecal pouches of a high percentage of the rock bass. Eggs near the genital opening contain fully formed miracidiae ready to hatch upon reaching the water. Hatching takes place quickly when they reach the water. The miracidium forces the operculum form the egg, emerges, and swims rapidly away. Upon striking an object, it adheres, never seeming to turn away.

      Infection of the rainbow clam first intermediate host (Eurynia iris) has not been observed. It is likely, however, that the miracidia are swept through the incurrent siphon into the branchial chamber, where they attach to the gonad and burrow into it. Up to 6 percent of the clams from some areas are naturally infected. Branching sporocysts develop in gonads, often completely filling them. While only a single generation has been reported, it seems probably that a mother sporocyst and daughter sporocycst occur. Early development of the cercariae in the sporocysts is rapid but the time required for reaching maturity is unknown. They emerge from the gonads into the branchial chamber. Currents of water flowing from the excutten siphon carry them away from the clams. Upon reaching the outside, they spread the long furcae and hang with the body downward swimming slowly.

      When the fish swim by, the furcae become entangled with the fins, holding the cercariae in a position that enables them to attach by the anterior holdfast and burrow into the tissues. As they work their way rapidly into the fins, the tail is discarded. Having entered the tissues, they move about, enlarging the space around them, and within an hour are enclosed in a hyaline cyst of parasitic origin.

      Infection of rock bass takes place when fish harboring the cysts are eaten. Upon being released by the action of the digestive juices, the metacercariae migrate into the cecal pouches and mature in 30 days” (Olsen, 1974).

    • Sources:Olsen O.W. 1974. Animal parasites, their life cycles and ecology. University Park Press, London, Baltimore & Tokyo, 3rd Revd Edn., p. 261.
    • APO Parasite Records: (by Life Cycle)

  • University of Colorado Boulder