Microcotyle polymixiae

Microcotyle polymixiae
Scientific classification
Kingdom:	Animalia
Phylum:	Platyhelminthes
Class:	Monogenea
Order:	Mazocraeidea
Family:	Microcotylidae
Genus:	Microcotyle
Species:	M. polymixiae
Binomial name
	Microcotyle polymixiae; Yamaguti, 1968

Last updated November 09, 2019

Microcotyle polymixiae is a species of monogenean, parasitic on the gills of a marine fish. It belongs to the family Microcotylidae. It was first described and illustrated based on 82 whole mounts, from the gills of the silver eye, Polymixia japonica (Polymixiidae) off Hawaii.^[1]

In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. 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. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined.

Fish are gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered paraphyletic by excluding the tetrapods. Because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology, unless it is used in the cladistic sense, including tetrapods. The traditional term pisces is considered a typological, but not a phylogenetic classification.

Microcotylidae is a family of polyopisthocotylean monogeneans. All the species in this family are parasitic on fish.

Description

Microcotyle polymixiae has the general morphology of all species of Microcotyle, with a flat lanceolate body, tapered anteriorly 3.5-8.5 mm in length, comprising an anterior part which contains most organs and a posterior part called the haptor. The haptor is symmetrical, hatchetshaped in profile and bears 57-88 clamps, arranged as two rows, one on each side(26-47 on the right and 27-47 on the left). The clamps of the haptor attach the animal to the gill of the fish. There are also two small buccal suckers strongly muscular, septate, unarmed and located at the anterior extremity. The digestive organs include an anterior, terminal mouth, a simple esophagus, a muscular rounded pharynx, and a posterior intestine with two lateral blind-ending branches terminating separately at posterior end of body proper. Each adult contains male and female reproductive organs. The reproductive organs include an anterior circular genital atrium opening a little in front of intestinal bifurcation., with spines, a dorsal vagina unarmed, opening middorsally just in front of body constriction, a single ovary, and 15 to 75 oval testes occupying the entire postovarian interintestinal field. The eggs are fusiforme with an anterior filament extremely fine, convoluted; and a posterior filament short, and usually curved.^[1]

The haptor is the attachment organ of the monogeneans, a group of parasitic Platyhelminthes. The haptor is sometimes called opisthaptor to emphasize that it is located in the posterior part of the body, and to differentiate it from the prohaptor, a structure including glands located at the anterior part of the body. According to Yamaguti (1963), the chief adhesive organ of the monogeneans, the haptor, is posterior, more or less discoid, muscular, may be divided into alveoli or loculi, is usually provided with anchors, has nearly always marginal larval hooklets, or is in a reduced form with anchors. The haptor may consist of symmetrical or asymmetrical, sessile or pedunculate, muscular suckers or clamps with or without supporting sclerites; accessory adhesive organs may be present in form of armed plaques, lappets or appendices.

Clamps are the main attachment structure of the Polyopisthocotylean monogeneans.
These ectoparasitic worms have a variable number of clamps on their haptor ; each clamp is attached to the host fish, generally to its gill. Clamps include sclerotised elements, called the sclerites, and muscles. The structure of clamps varies according to the groups within the Polyopisthocotylean monogeneans; microcotylids have relatively simple clamps, whereas gastrocotylids have more complex clamps.

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water and excretes carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are kept moist. The microscopic structure of a gill presents a large surface area to the external environment. Branchia is the zoologists' name for gills.

Etymology

The specific epithet polymixiae is probably after the genus of the host fish, Polymixia , but this is not explicated in the text of the original description by Yamaguti.^[1]

Polymixia is the only extant genus of the order Polymixiiformes and the only genus in Polymixiidae. It contains 10 species, all of which live in deepwater marine environments. They are found in tropical and subtropical waters of the Atlantic, Indian and western Pacific Oceans. They are bottom-dwelling fish, found down to about 800 m (2,600 ft). Most are relatively small fish, although one species is over 40 cm (16 in) in length.

Satyu Yamaguti was a Japanese parasitologist, entomologist, and helminthologist. He was a specialist of mosquitoes and helminths such as digeneans, monogeneans, cestodes, acanthocephalans and nematodes. He also worked on the parasitic crustaceans Copepoda and Branchiura. Satyu Yamaguti wrote more than 60 scientific papers and, more importantly, several huge monographs which are still in use by scientists all over the world and were cited over 1,000 times each.

Hosts and localities

The type-host is the Silver eye, Polymixia japonica (Polymixiidae). The type-locality is off Hawaii.^[1] No other mention of this parasite seems to exist in the scientific literature. Yamaguti ^[1] described two other species of Microcotyle from Hawai: Microcotyle bothi and Microcotyle emmelichthyops , from different host-fish.

Hawaii is a state of the United States of America. It is the only state located in the Pacific Ocean and the only state composed entirely of islands.

Microcotyle is a genus which belongs to the phylum Platyhelminthes and class Monogenea. Species of Microcotyle are ectoparasites that affect their host by attaching themselves as larvae on the gills of the fish and grow into adult stage. This larval stage is called oncomiracidium, and is characterized as free swimming and ciliated.

Microcotyle bothi is a species of monogenean, parasitic on the gills of a marine fish collected in Hawaii. It belongs to the family Microcotylidae.

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References

1 2 3 4 5 Yamaguti, S. (1968). Monogenetic Trematodes of Hawaiian Fishes. Honolulu: University of Hawaii Press.

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[Yamaguti1968-1] 1 2 3 4 5 Yamaguti, S. (1968). Monogenetic Trematodes of Hawaiian Fishes. Honolulu: University of Hawaii Press.