Date of Award


Document Type


Degree Name

Master of Science

Degree Discipline



The monogenetic trematodes are monoecious flatworms that are parasites of freshwater and marine fishes, as well as other aquatic vertebrates (amphibians and reptiles). They are found on the skin and in gill chambers, buccopharyngeal cavities, and other organs communicating directly or indirectly with the exterior (nostrils, ears, cloaca, rectal gland, urinary bladder).

Many of the parasites are host specific and will inhabit certain gill arches. They may occupy all four-gill arches or certain ones. Llewellyn (1956) reported that the posterior terminal part of the parasite is located closer to the host's gill arch and the anterior end is closer to the distal portion of the primary lamellae. The Monogenea move about their host in a leechlike manner, alternately attaching their pro-and opisthohaptors. The mouth is ventrally located and the helminths feeds on slime, epithelial cells, and blood exuding from places damaged by their hooks. The parasites may seriously injure the gills of their host, especially in the case of young fish. They usually range in size from 0.03 mm to 20 mm and the ventral side is slightly concave, while the dorsal one is usually flat.

The body is either colorless or grayish and is covered by a thin layer of noncellular cuticle. It is suspected that the cuticlesecreting cells have sunk into the parenchyma. A thin layer of circular muscles is below the protective cuticle. Beneath the circularly arranged muscles is a thin layer of well-developed longitudinal muscles. The region between the body wall and the internal organs is packed with a loose parenchyma consisting of cells, fibrils and spaces. The opisthohaptor is the chief organ of adhesion and is located posteriorly to the rest of the body. Its characteristics include those of being discoidal or subdivided into loculi. The anchors are located on the haptor along with marginal larval hooklets. Sometimes, the haptor may consist of symmetrical or asymmetrical muscular suckers which may or may not have supporting sclerites. The accessory organ may be present in the form of armed plaques, lappetts or appendices. Occasionally, there are glandular structures called head organs which empty into cephalic gland ducts that open along lateral margins of the head. Two pairs of eyes are present. The mouth is located terminally or subterminally. It may be surrounded by an oral sucker or provided with paired intrabuccal suckers. The intestine can bifurcate into branched or unbranched crura which becomes confluent posteriorly. In some cases, the vas deferens may wind around the intestinal limb.

Committee Chair/Advisor

J. E. Berry

Committee Member

L. C. Collins

Committee Member


Committee Member

E. W. Martin

Committee Member

B. K. Chopra


Prairie View Agricultural and Mechanical College


© 2021 Prairie View A & M University

Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Date of Digitization


Contributing Institution

John B Coleman Library

City of Publication

Prairie View




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