Homalometron pallidum

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Homalometron pallidum
Scientific classification
Kingdom:
Animalia
Phylum:
Platyhelminthes
Class:
Trematoda
Order:
Plagiorchiida
Family:
Apocreadiidae
Genus:
Homalometron
Species:
H. pallidum
Binomial name
Homalometron pallidum
Stafford, 1904 [1]

Homalometron pallidum is a species of marine trematodes in the family Apocreadiidae. It is an endoparasite of the mummichog, Fundulus heteroclitus, a small fish found in brackish water along the east coast of the United States and Canada. It has a complex life cycle and lives inside several different host species at different stages.

Contents

Description

The original description of Homalometron pallidum was given by Linton in 1899 and reads: [2]

"Body very minutely spinose, white, translucent; acetabuhuni and oral sucker about same size; outline of body, long oval; neck short, continuous with body; greatest breadth in region of testes, near posterior end; ecaudate; acetabuhum sessile; ranii of intestines simple, elongate ; esophagus as long as pharynx; testes, two, in median line behind uterus; seminal vesicle dorsal to ovary and posterior border of acetabulum; ovary between acetabulum and testes, on right side; pharynx, subglobular; genital aperture in front of acetabulum, on median line; vitelline glands lying at posterior end and along sides of body as far

as acetabulum; ova few, relatively large."

"Dimensions of specimen in formalin, given in millimeters: length, 2.72; breadth, anterior 0.43, at acetabulum 0.89, middle 1.07; near posterior 0.36 ; diameter of oral sucker, 0.26; diameter of acetabulum, 0.29; diameter of ovary, 0.21; diameter of testes, 0.33 and 0.39; ova, 0.11 and 0.07 in the two principal diameters."

Stafford used these diagnostic characteristics when he formally described the species in 1904. He was criticized for doing so in 1907 by the German parasitologist Arthur Looss who considered the description insufficient, pointing out that it was not possible to use this description to distinguish this species from other similar parasitic trematodes. [2]

Distribution

Homalometron pallidum is found on the eastern seaboard of Canada and the United States. Its range extends from Prince Edward Island and the Gulf of St. Lawrence southwards to the Gulf of Mexico. It is found in the tidal creeks, estuaries and salt water marshes where its host species occur. [3]

Life cycle

Homalometron pallidum can parasitise mummichogs, pictured Mummichog.jpg
Homalometron pallidum can parasitise mummichogs, pictured

Homalometron pallidum has a complex life cycle involving several host species. The adult worm lives in the gut of a small fish, the mummichog (Fundulus heteroclitus). [2] Eggs are ejected from the host fish in its faeces and are ingested by a small aquatic snail, Hydrobia minuta . This acts as a secondary host. When the eggs hatch, they develop in to rediae. These undergo asexual reproduction and multiply before becoming motile cercariae. The cercariae are few in number and large in size, in comparison to their small gastropod host. They emerge from the snail into the water at night and become free-living. They swim tail first with their body bent round and their tail lashing. They can also crawl with the use of two ventral suckers. They have penetration glands and make their way into an intermediate transfer host. Such hosts can include the amethyst gem clam Gemma gemma, another mummichog, or certain polychaete worms, but not other species of fish. In their new host, the cercariae become metacercariae by encysting in the tissues. In this inactive state, they wait to be ingested by a mummichog. In its gut, they develop into adult worms ready to undergo sexual reproduction and start the cycle again. [2]

Other fish have been identified as also acting as a host to the adult worms, including Menticirrhus saxatilis , Morone americana , Pseudopleuronectes americanus , Tautoga onitis , and Bairdiella chrysura . However, in some of these cases, the worm species could have been improperly identified. [2]

Related Research Articles

Mummichog

The mummichog is a small killifish found along the Atlantic coast of the United States and Canada. Also known as Atlantic killifish, mummies, gudgeons, and mud minnows, these fish inhabit brackish and coastal waters including estuaries and salt marshes. The species is noted for its hardiness and ability to tolerate highly variable salinity, temperature fluctuations from 6 to 35 °C, very low oxygen levels, and heavily polluted ecosystems. As a result, the mummichog is a popular research subject in embryological, physiological, and toxicological studies. It is also the first fish ever sent to space, aboard Skylab in 1973.

Trematoda A class of parasitic flatworms

Trematoda is a class within the phylum Platyhelminthes. It includes two groups of parasitic flatworms, known as flukes.

Digenea

Digenea is a class of trematodes in the Platyhelminthes phylum, consisting of parasitic flatworms with a syncytial tegument and, usually, two suckers, one ventral and one oral. Adults commonly live within the digestive tract, but occur throughout the organ systems of all classes of vertebrates. Once thought to be related to the Monogenea, it is now recognised that they are closest to the Aspidogastrea and that the Monogenea are more closely allied with the Cestoda. Around 6,000 species have been described to date.

<i>Echinostoma</i>

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<i>Fasciolopsis</i>

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<i>Nanophyetus salmincola</i>

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<i>Heterophyes heterophyes</i>

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<i>Telogaster opisthorchis</i>

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Megalodiscus temperatus is a Digenean in the phylum Platyhelminthes. This parasite belongs to the Diplodiscidae family and is a common parasite located in the urinary bladder and rectum of frogs. The primary host is frogs and the intermediate hosts of Megalodiscus temeperatus are freshwater snails in the genus Helisoma.

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<i>Gastrodiscoides</i>

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Telorchis is a genus of trematode parasites found in many herps, comprising around 70 species. This parasite is an indirect parasite, with a snail intermediate host and a reptile or amphibian definitive host. Typically found in the gastrointestinal tract of their definitive host, telorchids attach to the wall of the intestinal tract with their ventral sucker, or acetabulum.

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<i>Sibitrema</i>

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References

  1. ↑ Stafford, J. (1904). I. Wissenschaftliche Mitteilungen. 1. Trematodes from Canadian Fishes. Zoologischer Anzeiger, 27(16–17), 481–495.
  2. 1 2 3 4 5 Stunkard, Horace W. (1964). "The morphology, life history and systematics of the digenetic trematode Homalometron pallidum Stafford 1904" (PDF). The Biological Bulletin. 126 (1): 163–173. doi:10.2307/1539426.
  3. ↑ Fundulus heteroclitus heteroclitus FishBase. Retrieved 2012-03-06.
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