world of amoeboid organisms


Genus Nuclearia Cienkowsky, 1865

Diagnosis: Cell amoeboid, normally spherical to subspherical, with sharply pointed fine radiating pseudopodia; actively moving form varies in shape; cell readily adopt a flattened form without severe compression being applied; branching of pseudopodia occurs; with or without a mucous envelop; with one or many nuclei.

Ecology: Fresh water. Feeding by either ingestion of food particles or penetration of eukaryotic algal filaments.

Key to the species:

Note: the weak point of this key is that it is very difficult to detect any nucleus in a Nuclearia-species.

  1 Organisms not adopting a rounded form when free from compression 2
  – Organisms readily adopting a spherical form when uncompressed 9
  2 Organisms typically with 1, occasionally 2, nuclei 3
  – Organisms typically with more than 2 nuclei. The nucleoli appear spherical and smooth. Body diameter typically 30 – 60 µm. No cysts reported. Polymorphic, adopting either a spherical or flattened body form, and with or without a mucus sheath. Food includes filamentous blue-green algae. N. delicatula
  3 Nucleus without evident nucleolus. Body typically about 16 µm in diameter. A spherical and a flattened form have been described, but cysts and enveloping mucus sheath have not. N. polypodia
  – Nuclei with evident nucleolus 4
  4 Body typically 10 µm or less in length. The nucleoli appear spherical and smooth. A spherical form has not been described, nor have cysts nor an enveloping mucus sheath. N. leuckarti
  – Body typically 15 µm or more in length 5
  5 Body enveloped by mucus sheath through which radiating pseudopodia can protrude 6
  – Mucus sheath not evident 7
  6 Mucus sheath in 2 layers. Cells typically 30 µm in diameter, having one  nucleus with a smooth spherical nucleolus N. rubra
  – Mucus sheath single. see note below
  7 No cysts evident 8
  – Cysts produced See note below
  8 Body typically 15 µm in length. Only a flattened form has been described. The nucleolus is spherical and smooth. No cysts nor spherical form of the body have yet been described. N. moebiusi
  – Body  typically 30 µm in diameter. Two organisms,  N. rubra  and N. simplex satisfy this diagnosis See note below
  9 With evident enveloping mucus sheath 10
  – Without any evident mucus sheath 16
10 Sheath double N. rubra
  – Sheath single 11
11 Nuclei without any evident nucleoli 12
  – Nuclei with nucleoli 13
12 Cell body diameter typically about 15 µm N. polypodia
  – Cell body diameter typically about 30 µm. Only a spherical form with a single-layered mucus sheath has been described. No report of a flattened form nor of a cyst. N. flavescens
13 Nucleolus tends to spherical but has a folded appearance. The cell body is typically about 30 µm in diameter. The normal body form is spherical with a single-layered mucus sheath. A flattened form can be adopted under severe compression. Relatively immobile. N. radians
  – Nucleolus  spherical  and  smooth  in  appearance 14
14 With more than 2 nuclei N. delicatula
  – With 1, occasionally 2, nuclei. 15
15 Filopodia sometimes with knobs N. thermophila
  – Filopodia never with knobs; two polymorphic species satisfy this diagnosis, and can only be distinguished on the basis of appearance of other cells in the population See note below
16 With more than 2 nuclei N. delicatula
  – Uninucleate, or occasionally with 2 nuclei 17
17 Cysts also present. Could be 1 or 2 species N. simplex or
N. rubra
  – No cysts seen. Organisms satisfying this diagnosis could belong to 1 of 3 taxa N. simplex
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