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Distribution of Reticulomyxa filosa, Reticulomyxa cf. filosa
According to the presently known geographic range, Reticulomyxa filosa (Reticulomyxa cf. filosa) may be considered as a cosmopolitan species, even though records from the Southern Hemisphere are still missing. The distribution encompasses temperate to (sub)tropical regions. The occurrence of known strains – isolated in principally semi-natural environments and in potential natural vegetation – is documented from:
(1) rotted wood (1937: New York City/USA, Nauss 1949); and
aquatic habitats (freshwater)
(2) a depressed, soggy area among decaying leaves (1937 and later on: New York City/USA, Nauss 1949);
(3) a lake among Sphagnum and algal trichoms (“Brandenburg strain”: 1993, Möwensee/Brandenburg/Germany, Hülsmann 2006);
(4) aufwuchs at riverbanks of the middle Elbe (2014: near Schnackenburg/Lower Saxony/Germany, Dagmar Borgwardt (Berlin/Germany), pers. comm.).
Additionally, Reticulomyxa filosa was reported from anthropogenic biomes or artificial ecosystems (terrestrial, aquatic, semiaquatic):
(5) a shallow, zinc-coated through (about 4 m2 area) used for cultivation of aquatic plants, among characeans (“Bochum strain” 1982: greenhouse, Botanical Garden of the Ruhr-Universität Bochum/Germany, Hülsmann 1984, 2006);
(6) an aquarium (fish tank) (“Berkeley strain” 1984: Berkeley/California/USA, Koonce & Schliwa 1985; Mitchison 1986;
(7) garden soil periodically irrigated with tap water and suspensions of bakery yeast (1990: Berlin/Germany, Hülsmann, unpublished);
(8) paddy fields (1999: Saitama/Japan, Tsukii 1999);
(9) paddy fields (2004: Okayama/Japan, Tsukii 2004);
(10) paddy fields (2004: Saitama/Japan, Tsukii 2004);
(11) paddy fields (2007: Tochigi/Japan, Tsukii 2007);
(12) an aquarium (fish tank) (2011: Witten/Germany, Ralf Schulz (Breuker), Witten/Germany, pers. comm.).
From the above lists, the strains (3), (5), and (6) are well documented and considered to represent conspecific strains of the type material (2) (= Reticulomyxa filosa Nauss 1949). Due to its frequent accidental presence in artificial freshwater tanks or aquarium-like containers, Reticulomyxa filosa (or potentially related strains) may be treated as species or species complex whose cysts – as long as kept damp – may become quite easily spread by human activities (global trade in ornamental animals and plants, fishkeeping, fish farming, paddy field farming, agriculture etc.). It is likely that e.g. in aquarist forums, blogs and periodicals additional indications of the occurrence and macro shots or figures of Reticulomyxa cf. filosa exist, under misnomers such as “Amoeba porrecta”, “giant amoeba” or “aquatic slime mold”. In view of the huge dimensions of the world area harvested (ca. 165 million ha, FAO 2015), regions with moist natural and anthropogenic grasslands and native perennial plants and semiaquatic cultivars of Asian rice (Oryza sativa) and related Poaceae seem to be the hotspots of the presently known natural distribution. Consequently, Reticulomyxa spp. may be considered to appear indigenous to East Asia (and other regions with extensive cultivation of semiaquatic cereals). This working assumption may be also based on the fact that all successful and long-lasting cultivation attempts are centering on feeding protocols with corn products – such as wheat germ flakes, oat flakes, cooked rice grains etc. (Nauss 1949, Koonce & Schliwa 1985, Hülsmann 1986/2006, Wylezich et al. 2014).