Genus Reticulamoeba Grell, 1994


Diagnosis: Reticulamoeba species are amoebo-flagellate; they have a stationary, more or less flattened amoeboid stage, of roundish to irregular outline and measuring c. 3-8 mm across. Thin reticulopodia radiate outwards from around the cell across the substrate, fusing at points to form networks that radiate out across the substrate. The area covered by the granular reticulopodia can be orders of magnitude greater than that occupied by the cell itself. Bidirectionally streaming granules can be seen on the reticulopodia. The reticulopodia themselves can move slowly, rearranging the size and shape of the network formed. When feeding, the reticulopodia penetrate diatom frustules rather than phagocytosing whole diatoms.
Grell observed that networks from different individuals can fuse with each other, forming 'feeding communities', at least in R. gemmipara. He also describes a bi-flagellate stage, which is initially roundish in shape, becoming more irregular. These 'swarmers' or 'zoospores' have short anterior and long posterior flagella, and swim by active beating of the anterior flagellum, the posterior trailing behind. The flagellates can both swim and glide across a surface. They eventually settle, resorb their flagella and issue reticulopodia from around the cell, thereby transforming to the amoeboid stage.

Ecology: Mediterranean marine littoral zone, feeding on diatoms


Two known species:
R. gemmipara Grell, 1994
R. minor Grell, 1995

The main differences between R. gemmipara and R. minor are:
a) the flagellate and amoeboid stages of the latter are smaller,
b) flagellate formation in R. minor occurs by fission of the amoeboid stage, resulting in two, four, or more zoospores, whereas in R. gemmipara zoospores are formed by unequal fission (budding) from the edge of the amoeboid cell.

The reticulate amoeba morphotype is generally very poorly known. Further reading Bass et all, 2012.