Microworld

world of amoeboid organisms

Menu

Genus Microheliella Cavalier-Smith and Chao, 2012

Diagnosis: As for the order Microhelida.

 

Microheliella maris Cavalier-Smith and Chao, 2012

Diagnosis: Characters of the genus; cell body about 4 µm, axopodia about twice that but so slender that easily overlooked.

Ecology: brackish habitat. River Ebro Delta, Spain

Remarks: Microheliella maris is so small that it is hard to see morphological characteristics under the light microscope, but it can be recognized by four:

1) radiating axopodia,
2) central centrosome,
3) the nucleus situated aside from the cell centre,
4) absence of cilia.

This morphological combination is shared only with centrohelid heliozoa and gymnosphaerids; in the light microscope alone one cannot see their tiny extrusomes and cannot tell that the axopodia actually have microtubules, as shown here for the first time. Gymnosphaerids are far larger, more complicated and adaptively quite distinct; none of those known could be confused with Microheliella. It would be hard to separate Microheliella from the smallest scale-free centrohelids (Oxnerella, Chlamydaster); the smallest of these so far described is typically three times as large as Microheliella, but there is a new species of Oxnerella which is nearly as small (7 µm as opposed to Microheliella’s 4 µm (Chao and Cavalier-Smith, unpubl. observ.). It can be distinguished from Microheliella by careful light microscopy that reveals its much larger and more obvious extrusomes (Cavalier-Smith and Chao, 2012).

Similar looking amoeboids are specimens of the genus Limnofila, which are also very small, but lack microtubules.

Recent posts

Euglypha bryophila

Euglypha bryophila, after Brown, 1911 (L), from Ecuador (R) Euglypha bryophila  Brown, 1911 Diagnosis: (Original description) The test is very regular in form and subject

Read More »

Vernalophrys

(A) A Scenedesmus cell (arrow) is engulfed by a trophozoite. (B) Several Scenedesmus cells adhere to the surface of a plasmodium that has numerous vacuoles

Read More »

Actinosphaeridium spec.

Actinosphaeridium spec. Diagnosis: Cell surrounded by a membranous shell, with an outer mucous layer. Filopodia with granules, sometimes branching. Cell stalked. Ecology: I found this

Read More »

Euglyphidion

Euglyphidion enigmaticum – after Bonnet, 1960 Genus Euglyphidion Bonnet, 196 Diagnosis: Shell hyaline, ovoid, pseudostome circular or slightly elliptical. Shell loosely covered with two types of

Read More »

Leptomyxa spec.

Leptomyxa sp., slowly retracting in response to the light of the microscope Leptomyxa sp. Diagnose: This is a very large amoeba which I found in

Read More »

Zivkovicia spec.

Zivkovicia spec., 200 µm long; the right image is viewed through the aperture Zivkovicia spec.  Diagnosis: Shell pyriform, circular in oral view, with a clear

Read More »