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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.

  1Organisms not adopting a rounded form when free from compression2
  –Organisms readily adopting a spherical form when uncompressed9
  2Organisms typically with 1, occasionally 2, nuclei3
  –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
  3Nucleus 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 nucleolus4
  4Body 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 length5
  5Body enveloped by mucus sheath through which radiating pseudopodia can protrude6
  –Mucus sheath not evident7
  6Mucus sheath in 2 layers. Cells typically 30 µm in diameter, having one  nucleus with a smooth spherical nucleolusN. rubra
  –Mucus sheath single.see note below
  7No cysts evident8
  –Cysts producedSee note below
  8Body 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 diagnosisSee note below
  9With evident enveloping mucus sheath10
  –Without any evident mucus sheath16
10Sheath doubleN. rubra
  –Sheath single11
11Nuclei without any evident nucleoli12
  –Nuclei with nucleoli13
12Cell body diameter typically about 15 µmN. 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
13Nucleolus 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  appearance14
14With more than 2 nucleiN. delicatula
  –With 1, occasionally 2, nuclei.15
15Filopodia sometimes with knobsN. 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 populationSee note below
16With more than 2 nucleiN. delicatula
  –Uninucleate, or occasionally with 2 nuclei17
17Cysts also present. Could be 1 or 2 speciesN. simplex or
N. rubra
  –No cysts seen. Organisms satisfying this diagnosis could belong to 1 of 3 taxaN. simplex
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