Clinostomum Marginatum
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''Clinostomum marginatum'' is a
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of
parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The ent ...
fluke (class
Trematoda Trematoda is a class of flatworms known as trematodes, and commonly as flukes. They are obligate internal parasites with a complex life cycle requiring at least two hosts. The intermediate host, in which asexual reproduction occurs, is a mol ...
). It is commonly called the "Yellow grub". It is found in many
freshwater fish Freshwater fish are fish species that spend some or all of their lives in bodies of fresh water such as rivers, lakes, ponds and inland wetlands, where the salinity is less than 1.05%. These environments differ from marine habitats in many wa ...
in North America, and no fish so far is immune to this parasite. It is also found in frogs. ''Clinostomum marginatum'' can also be found in the mouth of aquatic birds such as
heron Herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 75 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genus ''Botaurus'' are referred to as bi ...
s and
egret Egrets ( ) are herons, generally long-legged wading birds, that have white or buff plumage, developing fine plumes (usually milky white) during the breeding season. Egrets are not a biologically distinct group from herons and have the same build ...
s. They are commonly present in the esophagus of fish-eating birds and reptiles. Eggs of these trematodes are shed in the feces of aquatic birds and released into water. Aquatic birds become hosts of this parasite by ingesting infected freshwater fish. The
metacercariae Trematodes are parasitic flatworms of the class ''Trematoda'', specifically parasitic flukes with two Sucker (zoology), suckers: one ventral and the other Mouth, oral. Trematodes are covered by a Tegument (helminth), tegument, that protects the o ...
are found right beneath the skin or in the muscles of host fish. The life cycle of the fluke consists of two intermediate hosts and one definitive host. The parasite's eggs hatch in the water and the miracidium invades the foot of a snail. The cercaria leaves the snail and encysts in the muscle of the connective tissue of fresh-water fish species or in the muscle of frogs. The metacercarial stage is that is formed is then referred to as the “yellow grub”. The encysted metacercariae appear yellow, with a slightly oval-shaped spot, and are about 3 to 6 mm long. Metacercariae are common in the caudal, dorsal, and pectoral fins; on the inside surface of the operculum, and in the flesh. The adult trematode is found in the mouth and esophagus of herons and other fish-eating birds.


Morphology

''Clinostomum marginatum'' is a yellow flatworm that can grow up to in the flesh of freshwater fish or the muscle of frogs. Distinguishing characteristics of this parasite in the "miracidium" stage are three eyespots located on the mid-dorsal line, posterior of lateral papillae. These eyespots are cup-shaped and contain a lens, forming a triangle-shaped appearance on the parasite. They also contain two pairs of
flame cell A flame cell is a specialized excretory cell found in simple invertebrates, including flatworms ( Platyhelminthes), rotifers and nemerteans; these are the simplest animals to have a dedicated excretory system. Flame cells function like a kidney ...
s; one pair located on the anterior between the eyespots and lateral papillae and one pair on the posterior side. In addition, they have pairs of large refractive vacuoles, which are found near the flame cells. They differ in structure and physiological phenotypes depending on its habitat. However, specimens found in herons were smooth, had thick teguments, and absorbed food (such as glucose) through facilitated diffusion. Along with a thick tegument, these flukes were also found to have
bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
on them. The bacteria may play a role in the absorption and
metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...
of
glucose Glucose is a sugar with the Chemical formula#Molecular formula, molecular formula , which is often abbreviated as Glc. It is overall the most abundant monosaccharide, a subcategory of carbohydrates. It is mainly made by plants and most algae d ...
.


Life cycle

For its
life cycle Life cycle, life-cycle, or lifecycle may refer to: Science and academia *Biological life cycle, the sequence of life stages that an organism undergoes from conception to reproduction *Life-cycle hypothesis, in economics *Erikson's stages of psy ...
to be complete, ''Clinostomum marginatum'' requires two
intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include ...
s (snail and fish or frog) and one
definitive host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' (symbiont). The guest is typically provided with nourishment and shelter. Examples include ...
(bird). The life cycle begins when eggs hatch in the water. The miracidia swims and invades the foot of a snail of the genus '' Helisoma''. They will die in several hours if they cannot find the snail host. While inside the snail, the miracidia undergo several
asexual reproduction Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the f ...
and the larvae eventually become cercariae. The cercariae form exits the snail and is free swimming in water, in search for a fitting fish host. They burrow inside the fish or frog host, and the cercariae encyst and continue its next larval stage, known as "metacercariae", which are the yellow grubs. The grubs can live within the host for several years until eaten by a bird host. When the parasitized host is eaten, the grub matures in the throat of the bird. The eggs of the parasite known as a metacercariae are then released into the water through the bird's mouth when feeding and become adult flukes. This completes the life cycle.


Food source

These parasites may feed on the mucus of organs, food content ingested by the host, blood and tissue from eroding epithelial surfaces.


References


General references

* * * * * * * * * * * * * {{Taxonbar, from=Q3381439 Diplostomida Trematodes parasiting fish Parasites of birds Animals described in 1819 Taxa named by Karl Rudolphi