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