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The World of Protozoa, Rotifera, Nematoda and Oligochaeta


Nucleosphaerium Cann & Page, 1979 (ref. ID; 4670 original paper)

Phylum Sarcomastigophora Honigberg & Balamuth, 1963: Subphylum Sarcodina Hertwig & Lesser, 1874: Superclass Rhizopoda von Siebold, 1845: Class Filosea Leidy, 1879: Order Aconchulinida De Saedeleer, 1934: Family Nucleariidae nov. fam. (ref. ID; 4670 original paper)

[ref. ID; 4224]
Cells always spherical, except when feeding. With radiating filose pseudopodia. Branching of pseudopodia not observed. Relatively inactive. Feeding by ingestion. No penetration of either healthy or old/damaged eukaryotic algal filaments. (ref. ID; 4224)

[ref. ID; 4670]
Cells always spherical with radiating filose pseudopodia. Branching of pseudopodia not observed in known species. Not motile. Feeding by ingestion, not penetration of algae. Nucleus in the one described species with a single central nucleolus. (ref. ID; 4670)
  1. Nucleosphaerium radians comb. nov. (ref. ID; 4224)
    Syn; Nuclearia radians (ref. ID; 4224)
  2. Nucleosphaerium tuckeri Cann & Page, 1979 (ref. ID; 4670 original paper) reported year? (ref. ID; 4224)

Nucleosphaerium tuckeri Cann & Page, 1979 (ref. ID; 4670 original paper) reported year? (ref. ID; 4224)


Cell spherical, mean 30 um in diameter, with radiating, non-branching filose pseudopodia. Mucilaginous coating, usually with adherent bacteria. Numerous contractile vacuoles. Large central nucleus with central nucleolus, sometimes appearing slightly lobed. Endozoic bacteria in cytoplasm. Reproduction by binary fission. (ref. ID; 4670)


Light microscopy showed the cell form to be spherical with a diameter of 10 um to 50 um. The average diameter of 100 cells was 30 um. The spherical form is observed on the bottom of a glass dish, and elongated forms are never normally observed unless the cells are actively feeding on algal filaments, when the cells may become spindleshaped but never flattened. There is no obvious hyaline region when the cells are examined by light microscopy, the cytoplasm appearing slightly granular. Fine filose pseudopodia up to three times the cell body diameter radiate from all regions of the cell surface. The width of the filose pseudopodia at their proximal ends ranges from 0.3 um to 0.7 um, and they taper to a fine terminal end. Pseudopodia up to 100 um in length were seen radiating from larger cells. They are seen to extend and withdraw, taking an average of 40 sec to extend fully, and only 16 sec to withdraw totally. Branching of the pseudopodia was not observed. No axonemes were observed by light microscopy. There is usually "halo" of what appear to be bacteria adherent to an exterior mucilaginous coating. These are approximately 1.5 um in length by 0.7 um in width. The Gram stain showed the presumed bacteria to be Gram negative. The mucilaginous coating on average extends 7 um around the cell. A pink colouration of the coat after the PAS procedure indicates that it is a mucopolysaccharide layer. When the cells are fixed in 2% osmium tetroxide, the coating appeared to be composed of three distinct layers. The bacteria soon disperse when a cover slip is placed over the specimen. The cells are devoid of any form of locomotion, the only movement observed being due to currents present in the medium. In feeding, the cell appears to ingest one end of an algal filament as far as possible, and then rapidly expel it, the process taking under a minute to complete. Eventually a length is completely engulfed a round vacuole fully formed around it. Food vacuoles range in size from 9.5 um (with little contents remaining), to a recently formed vacuole which is as long as the engulfed food particle and usually up to 30 um in length. Food vacuoles containing algal remains in varying stages of digestion can be observed. Presumably the active ingestion and expulsion of the algal filament finally serves to break off a suitable length, which can be totally engulfed by the cell, although this was not actually observed. Under a sealed coverslip the cell soon takes on an irregular form, and the cell contents can be more easily observed. However, abnormal processes are produced which can exhibit active cytoplasmic streaming, and the cell rapidly changes shape. Some of the remaining filose pseudopodia were observed to contain small swellings which travelled towards the cell body. The nucleus is central, approximately spherical and 12 um in diameter in the average-sized organism, and the central nucleolus is 5 um in diameter. Contractile vacuoles are numerous and become more obvious when the cells have been left under a sealed cover slip for several minutes. Vacuoles reach a maximum diameter of 4 um, empty quickly, and fill again in approximately 42 seconds, under the condition described under Methods. No crystals were observed in the cytoplasm. Reproduction is by binary fission, the two daughter cells being finally connected by a thin cytoplasmic strand. A flattened locomotive form of this organism was not observed over a period of seven years in culture. Electron-microscope examination shows the cell to be bounded by single plasma membrane. The mucilaginous coat was not present after material had been fixed for sectioning. Glycocalyces in the usual sense are retained by electron-microscopical fixation procedures. Pseudopodia in section contained cytoplasm of the same nature as that found inside the cell, although alignments of very filaments are possibly present. They also contained inclusions which are membrane bound, and up to 1 um in length. The nucleus contained a large, lobed nucleolus. Nuclear pores of 0.08 um are observed in most regions of the nuclear membrane. The nuclear envelope consisted to two membranes with a gap of varying thickness. Mitochondria, found throughout the cell, range from 0.4 um to 0.8 um in length and 0.32 um to 0.48 um in width. The tubular cristae are at varying angles to the mitochondrial membrane and are unbranching. Endozoic bacteria are found in all regions of the cytoplasm and are approximately 0.6 um in length, although when dividing, bacteria reach 1.2 um. They are all membrane-bound. Dictyosomes were closely associated with the nucleus, and a maximum of four were observed in one single plane. The thickness of each saccule is on average 22 nm, and the distance across the stack of saccules 1 um. Vesicles associated with the dictyosomes are concentrated around the region of the nucleus and are up to 0.2 um in diameter. Food vacuoles were observed in several cells, the larger ones approximately 12 um by 8 um. Thylakoid remains of the algal food are clearly visible. Other vacuoles are observed throughout the cell and range in size from 0.4 to 4 um in diameter. No centrioles or microtubules were observed in the cytoplasm of the sections of Nucleosphaerium which were examined. (ref. ID; 4670)