Haplomyxa retiforma Siemensma and Holzmann, 2023
Diagnosis. Naked multinucleated cell without distinct shape. The whole cell body can transform into a large flat extended reticulum with many branches and holes up to 3,500 µm long and 70 µm wide, but cells can also be globular or irregularly shaped. Cytoplasm with bi-directional streaming, producing a few large and extended pseudopodial strands and a network of numerous interconnected granuloreticulopodia. Cytoplasm with numerous cytoplasmic granules and contractile vacuoles. Hundreds of small spherical nuclei with nucleoli scattered along the nuclear membrane, diameter 5.7-6.7 µm. Migration through one large leading pseudopodial strand.
Ecology. (Type locality) The upper layer of organic-rich sediment of a very shallow pond, some cm deep, in nature reserve Lagieskamp, Netherlands (52°16’39.6″N 5°08’22.4″E). This species was also collected from submerged basalt blocks at the foot of the northern dike of Gooimeer (Lake Gooi), Netherlands, May 2020 (52° 18’17.7 “N 5° 18’51.6” E).
Description. The cell usually consists of an elongated central body mass, about 700 µm in length and 130 µm width, and can reach up to 3,500 µm in length and 70 µm in width when moving. The cell can change it shape from rod-like to spherical or irregular. Commonly, two or three pseudopodial strands emerge from two terminal opposite apertures building an elaborate granuloreticulopodial network. Numerous thin anastomosing granoreticulopodia emerge from the cell body. Sometimes the cell body transforms into a wide spaced flat reticulum with relatively thin branches. The cell cytoplasm is packed with granules and vacuoles, but no crystalline inclusions were observed. A piece of plasma, removed from the main body when pipetted into guanidine, was observed under the light microscope. Many small spherical nuclei could be observed. In each nucleus, pieces of nucleolar material are scattered along the nuclear membrane resembling a thin ring. The diameter of the nuclei is 5.7-6.7 µm (mean 6.2 µm, n=30). Migration to a new location takes place by transferring the whole cytoplasm through a large pseudopodial strand. During migration, plasma blobs occur on reticulopodia. No cysts or division was observed during the ten days the type specimen survived in a petri dish.
Differential diagnosis. Morphologically H. retiforma can be distinguished from H. saranae by its larger nuclei, about 6 µm versus 2-4 µm respectively. The obtained sequences of H. retiforma contain 366 to 368 nucleotides. The GC content amounts to 32%.
Observed food. Various types of algae, e.g. Closterium sp., Euglena sp., Phacus sp., filamented green algae, blue algae, diatoms.
