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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Stygamoeba

Stygamoeba Sawyer, 1975 emend. Smirnov, 1995/96 (ref. ID; 4874)

Phylum Rhizopoda Von Siebold, 1845 (ref. ID; 4874)

[ref. ID; 4874]
Locomotive form thin and elongate resembling tooth-picks or splinters but capable of temporarily acquiring a forked or branched morphology. Anterior hyaloplasm can form very narrow, lateral hyaline extensions in some moving amoebae. Locomotion by steady cytoplasmic flow although cytoplasmic streaming difficult to observe. In non-directed movement, or when stationary, amoebae can adopt a broad, leaf-like shape, the body of which may be branched. Floating form with radiating pseudopodia in known species. At the ultrastructural level, in the case of the only species studied, the cytoplasm contains dictyosomes and mitochondria with flattened cristae. The cell coat consists of a thin, undifferentiated glycocalyx. Cells uninuleate. No flagellate stage in the life cycle. (ref. ID; 4874)
Type species; Stygamoeba polymorpha Sawyer, 1975 (marine) (ref. ID; 4874)

[ref. ID; 5694]
Amoeboid protists. (ref. ID; 5694)
  1. Stygamoeba polymorpha Sawyer, 1975 (ref. ID; 4874) reported year? (ref. ID; 3847)
  2. Stygamoeba regulata Smirnov, 1995/96 (ref. ID; 4874 original paper)

Stygamoeba polymorpha Sawyer, 1975 (ref. ID; 4874) reported year? (ref. ID; 3847)

Descriptions

Marine amoebae. (ref. ID; 3847)

Type locality

From the Western and North Atlantic Ocean. (ref. ID; 4874)

Stygamoeba regulata Smirnov, 1995/96 (ref. ID; 4874 original paper)

Differential diagnosis

Stygamoeba regulata differs from S. polymorpha in that it has a much more regular locomotive form and has a distinct uroid during locomotion. When not moving, or during non-directed movement, S. regulata never adopts the markedly branched form characteristic of S. polymorpha. Moreover, it has a distinct vesicular nucleus unlike S. polymorpha which lacks a discernible nucleolus at the LM level. It should also be noted that the locomotive forms of S. regulata, under LM, sometimes resemble Hartmannella spp. But the shape of the amoebae in non-directed movement or when stationary distinguishes these two genera at the LM level while the form of mitochondrial cristae and presence of the dense cytoplasmic bodies is an important and distinguishing feature at the ultrastructural level. (ref. ID; 4874)

Descriptions

The anterior hyaloplasm occupies 1/4 to 1/3 of the total cell length, and sometimes forms very narrow lateral extensions. At the posterior, a bulbous uroid is common. Furcation of the anterior end common when actively moving cells change direction of locomotion. Amoebae never considerably branched. Floating form with 3-6 thin, hyaline pseudopodia with rounded ends. Lengths 2-3 times greater than the diameter of the central cytoplasm mass. Nucleus of vesicular type, spherical or elongate, about 2.5 um in diameter, no nuclear lamina. Central nucleolus about 1.5 um in diameter. Thickness of glycocalyx about 13 nm. Electron-dense bodies obvious in the cytoplasm. Cysts spherical, with a single wall about 100 nm thick. (ref. ID; 4874)

Type locality

The upper layer of sediments in Niva Bay, The Sound, Denmark, where salinities were about 15 0/00. Can also multiply in marine water with full salinity around 35 0/00. (ref. ID; 4874)

Type slides

Holotype: preparation number 1995:2:9:1, paratype number 1995:2:9:2. Type slides and a 15 minutes video-recording of live amoebae (provisional number: 1995:2:9:1a) are deposited in the Natural History Museum, London, U.K. (ref. ID; 4874)

Measurements

Length of the locomotive form ranges between 19-38 um (average 27 um), and the breadth between 3.4-5.7 um (average 4.6 um); L/B ratio 4-8.6 (average 6.1). (ref. ID; 4874)