Pseudomonilicaryon anser
Pseudomonilicaryon anser is a species of unicellular ciliates 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". 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. The macronucleus of "Pseudomonilicaryon" is arranged like a string of beads, whereas that of "Dileptus" is composed of small nodules  scattered throughout the cytoplasm of the cell. 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 moved the species to the new genus "Dileptus". However, Dujardin's "Dileptus anser" was actually a misidentified specimen of "Dileptus margaritifer (Ehrenberg, 1834"), a dileptid of similar size with a shorter proboscis and scattered macronucleus. In 1931, Alfred Kahl entrenched the error  by treating "D. margaritifer" as a synonym of "D. 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 of "Vibrio anser" (Müller, 1773). 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) 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 surface is a row of 15-20 contractile vacuoles. 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. "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 extrusomes are released, disabling the smaller organism, which is then gathered into the dileptid's cytostome. 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."