Cucurbitella vlasinensis Ogden and Zivkovic, 1983
Diagnosis: Shell brown or opaque, subcircular or ovoid, with a distinct apertural collar; shell composed of a mixture of small to medium pieces of quartz to give a rough surface, but arranged so that the outline is more or less regular; particles are packed close together, with only small areas of organic cement visible; cement in the form of a network whose mesh is covered by a smooth membrane; collar trilobed and composed of small pieces of quartz arranged randomly; a double thickness of particles strengthens the three tooth-like projections where they form a dividing banier with the inner apertural opening; these ‘teeth’ are usually well defined and composed of small particles; each lobe has a small recess or cavity so that the internal opening is smaller than the external collar, the floor of these recesses appears as a continuation of the shell matrix; apertural opening trilobed in sequence with the collar and lined with flattish pieces of quartz with smaller pieces filling the junctions. Nucleus vesicular, with a spherical, hollow nucleolus.
Dimensions: Length 81-113 µm, breadth 69-97 µm, diameter of collar 36-51 µm, depth of collar 9-16 µm, diameter of aperture 19-35 (n=41) µm; my measurements 110-115 µm long, nucleus 34 µm.
Ecology: On waterplants and in sediment. Rare.
Remarks: This species resembles Difflugia lobostoma and large specimens of Difflugia gramen. Both species can have a collar, made of small particles. The main difference is the high collar of Cucurbitella vlasinensis. I found this remarkable species in the sediment of a ditch with Sphagnum contact in the nature reserve Naardermeer (south of De Machine) in the Netherlands.
I found this species also in a sample from Cocococha Lagoon in Peru. Specimens from this location were more spherical and larger, had a more pronounced collar and a much narrower diaphragm. The nucleus has two large nucleoli.
Ogden and Zivkovic, 1983: “In a review of the genus Cucurbitella by Gauthier-Lièvre & Thomas (1960) the number of lobes surrounding the aperture was used to differentiate species into a number of varieties and forms. Ogden (1986) considered that the three and four lobed specimens of C. mespiliformis were otherwise identical in all but that feature, and should therefore be designated as a single species until adequate morphological information was available on the variability of lobe formation. Nevertheless, observations on many specimens by Ogden show that there is little or no variation in the number and shape of the lobes. C. vlasinensis is similar to C. modesta Gauthier-Lièvre & Thomas, 1960 and C. modesta forma trilobata Gauthier-Lièvre & Thomas, 1960. It differs from C. modesta, which has four lobes, in that feature and general measurements, and from C. modesta forma trilobata in having well-defined teeth, a more extensive inner lining to each lobe and in overall larger general dimensions.
An interesting ecological point to note is that C. modesta forma trilobata was reported only from Morocco which has similar climatic conditions to the region of Yugoslavia where the type species were collected.
This species is named after the location where the samples were collected, Lake Vlasina.”