Saccamoeba stagnicola CCAP 1527/3. Locomotive forms, cysts. Olympus BH2, DIC. Scale 20 mkm. Photo: A.Smirnov   An amoebae strain from Valamo Island (North-Western Russia) that I beleive to be Saccamoeba stagnicola. Cyst structure of this strain (not illustrated) corresponds to that of S. stagnicola shown above. MBI 15-2, Phase contrast. Scale 20 mkm. Photo: A.Smirnov Basic references for identification: Page F.C. (1974) A further study of taxonomic criteria for Limax amoebae, with description of new species and a key to genera. Arch.Protistenk. 116:149-184 Page F.C. (1985) The limax amoebae: comparative fine structure of the Hartmannelidae (Lobosea) and further comparisons with the Vahlkampfiidae (Heterolobosea). Protistologica 21: 361-383 Page F.C. 1988. A new key to freshwater and soil gymnamoebae. FBA, Ambleside. 122p. Page F.C. 1991. Nackte Rhizopoda. in: Protozoenfauna, b.2. Gustav Fisher, Stuttgart. 3-172.

Saccamoeba stagnicola Page, 1974 CCAP 1527/3 (Strain originating from F.C. Page, but not the type strain) Limax amoeba, subcilindrical in cross-section, slightly clavate in locomotion. Frontal hyaline cap is not very obvious, and often is invaded with the stream of small granules (but not crystals or any other larger inclusions) from the granuloplasm. Single contractive vacuole is often located posteriorly or, rare, in the uroid. Typical villous-bulbous uroid present in most of specimens (uroidal villy may be not evident under low magnifications, and the uroid may appear to be morulate or bulbous). Few trailing uroidal filaments may be seen in amoebae moving in the liqud culture. Length of the locomotive form 30-75 mkm (average 50 mkm); Length/Breadth ratio about 4.2 Floating form rounded, urregular, with 4-8 short, thick, twisted pseudopodia Uninucleate, vesicular nucleus 4.5 - 8.5 mkm in diameter (average 6.5 mkm). Single, central nucleolus often conetins large lacune and appears to be ring-shape in LM. Cell contains a number of bypiramidal and plate-shaped crystals in the cytoplasm. Cysts rouned, single-walled, 12-19 mkm in diameter (average 15 mkm). The capacity to form cysts may be lost during the maintenance of cultures. The strain, illustrated here, formed cysts only in the liquid culture, but not on the agar. Cell coat in TEM often appears to be amorphous, in teh most sucessful preparations it is possible to distinct very fine cup-like pentagonal structures on the cell surface. Page (1988; 1991) noted that S.stagnicola often has elongate mitochondria, in contrast with S. limax. Despite the seemingly obvious appearnace the identification of S. stagnicola may be a challenging task. All limax amoebae are generaly very similar, and it is hard to beleive that their real diversity is limited with few curently named species. I would offer to assign an isolate to this species only in case of exceptionally good fitting of all observed features to the descriptions by Page (1974; 1988; 1991) and the current description. The only features that distinct S. stagnicola from S.limax are the size of the cell (S. limax is generally larger and more clavate, if to consider Page's strains), the number of crystals (there is much less of them in S. stagnicola and they are more fine) and the cyst structure. TEM is not of much use in species identifiation for hartmannellids, as the observed details of the ultrastructure of the cell are in great dependence of the fixation artefacts caused by osmotic shock, differences in the penetration rate of the fixatives and other reasons. I would offer even not to rely on the shape of mitochondria, as it is highly variable. SSU rRNA sequence of both S. stagnicola and S. limax are available from the GeneBank and the comparison of sequences may be very valuable addition for precise identification of saccamoebians. Back to checklist of species