''Pseudomonilicaryon anser'' is a species of

unicellular A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic organisms and ...

ciliate The ciliates are a group of alveolates characterized by the presence of hair-like organelles called cilia, which are identical in structure to flagellum, eukaryotic flagella, but are in general shorter and present in much larger numbers, with a ...

s in the family Dileptidae, also known under the names ''Dileptus anser'' and ''Dileptus cygnus''. The species is common in fresh water ponds, stagnant pools, mosses and soils. For nearly a century and a half, the species was classified in the genus ''

Dileptus ''Dileptus'' is a genus of unicellular ciliates in the class Litostomatea. Species of ''Dileptus'' occur in fresh and salt water, as well as mosses and soils. Most are aggressive predators equipped with long, mobile proboscides lined with toxic ...

''. In 2012, following a comprehensive review of the dileptid group, it was moved to the genus ''Pseudomonilicaryon'', which is distinguished from ''Dileptus'' by the shape of its

macronucleus A macronucleus (formerly also meganucleus) is the larger type of nucleus in ciliates. Macronuclei are polyploid and undergo direct division without mitosis. It controls the non-reproductive cell functions, such as metabolism Metabolism (, ...

. The macronucleus of ''Pseudomonilicaryon'' is arranged like a string of beads, whereas that of ''Dileptus'' is composed of small nodules scattered throughout the

cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...

of the cell.Vďačný, Peter, and Wilhelm Foissner. Monograph of the dileptids (Protista, Ciliophora, Rhynchostomatia). Land Oberösterreich, Biologiezentrum/Oberösterreichische Landesmuseen, 2012: 361-70

History and classification

''Pseudomonilicaryon anser'' has had a long and confusing history, complicated by a series of name changes and misidentifications. The species was first described and illustrated by Otto Müller in 1773, under the name ''Vibrio anser'', and redescribed by Ehrenberg in 1838, as ''Amphileptus anser''. In 1841,

Félix Dujardin Félix Dujardin (5 April 1801 – 8 April 1860) was a French biologist born in Tours. He is remembered for his research on protozoans and other invertebrates. Biography In 1840 Dujardin was appointed professor of geology and mineralogy at t ...

moved the species to the new genus ''

''. However, Dujardin's ''Dileptus anser'' was actually a misidentified specimen of ''Dileptus margaritifer (Ehrenberg, 1834''), a dileptid of similar size with a shorter

proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular arthropod mouthparts, mouthparts used for feeding and sucking. In vertebrates, a pr ...

and scattered macronucleus. In 1931, Alfred Kahl entrenched the error by treating ''D. margaritifer'' as a

synonym A synonym is a word, morpheme, or phrase that means precisely or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are a ...

of ''D. anser''. Muller vibrio anser

The identity of ''Dileptus anser'' is also entangled with that of another long-necked dileptid, the nominal species ''Dileptus cygnus (Clap. & Lach., 1859)''. Kahl describes and illustrates ''Pseudomonilicaryon anser'' under this name, and most studies of the organism have used this nomenclature. In 1984, ''Dileptus cygnus'' was formally identified as a

junior synonym In taxonomy, the scientific classification of living organisms, a synonym is an alternative scientific name for the accepted scientific name of a taxon. The botanical and zoological codes of nomenclature treat the concept of synonymy differently. ...

of ''Vibrio anser'' (Müller, 1773).Wirnsberger, Von Erna, Wilhelm Foissner, and Hans Adam. "Morphologie und Infraciliatur von ''Perispira pyriformis'' nov. spec., ''Cranotheridium foliosus'' (Foissner, 1983) nov. comb. und ''Dileptus anser'' (OF Müller, 1786)(Protozoa, Ciliophora)." Archiv für Protistenkunde 128.4 (1984): 305-317. In 2012, Peter Vďačný and Wilhelm Foissner transferred ''Dileptus anser'' to the genus ''Pseudomonilicaryon'' Foissner, 1997.

Morphology

''Pseudomonilicaryon anser'' is about .5 mm long, with a narrow, flattened body tapering at the posterior into a distinct tail. At the front end, is a long, extremely mobile proboscis, making up about 55% of the cell's entire length. The oral aperture (

cytostome A cytostome (from ''cyto-'', cell and ''stome-'', mouth) or cell mouth is a part of a cell specialized for phagocytosis, usually in the form of a microtubule-supported funnel or groove. Food is directed into the cytostome, and sealed into vacu ...

) sits at the base of this proboscis, within a visible swelling called the "oral bulge." The macronucleus is composed of 7 to 25 nodules, like a string of beads. Along the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

surface is a row of 15-20

contractile vacuole A contractile vacuole (CV) is a sub-cellular structure (organelle) involved in osmoregulation. It is found predominantly in protists, including unicellular algae. It was previously known as pulsatile or pulsating vacuole. Overview The contrac ...

Habitat and feeding

''Pseudomonilicaryon anser'' is found in mud and soft sediments at the bottoms of stagnant ponds and puddles. A rapacious predator, described by one writer as "surely the king of beasts of the Protozoa," it feeds exclusively on other microscopic organisms.Hausman, Leon Augustus. "Observations on the Ecology of the Protozoa." American Naturalist (1917): 168. ''P. anser'' hunts by clinging to the substrate and waving its long proboscis in a counter-clockwise direction. When the proboscis makes contact with its prey, toxic

extrusome Extrusomes are membrane-bound organelles found in eukaryotic cells that are capable of discharging material contained within to the exterior of the cell. Due to the diversity in structure and function, it is unlikely that different types of extruso ...

s are released, disabling the smaller organism, which is then gathered into the dileptid's

. Smaller prey are swept into the mouth by the movement of cilia, while large organisms are pushed toward the oral bulge by "the writhings of the proboscis."

References

{{Taxonbar, from=Q5276757 Protists described in 2012 Litostomatea Ciliate species