FAMILY NETZELIIDAE KOSAKYAN ET AL., 2016

Type species: Netzelia oviformis (Cash, 1909).

Updated diagnosis: Globular or oviform tests, with radial symmetry. Aperture is central, regular or lobed and forms a collar towards the outside of the test. Presence of irregular, ‘nail’-shaped idiosomes or/and exogenous materials, when these are available.

Included taxa: (Supporting Information, Appendix S1).

Difflugia lobostoma Leidy, 1874 and Difflugia lithophila Penard, 1902 share many traits with members of the genus Netzelia, such as Netzelia achlora (Penard, 1902), Netzelia gramen (Penard, 1902) and Netzelia oviformis (Cash, 1909), placed in the genus Netzelia by Gomaa et al. (2017). The main reason for the similarity between these species was the capacity to build a test with idiosomes independently from the presence of building material (Ogden, 1979). Later works showed that Difflugia lobostoma also had this ability, justifying its inclusion within the genus Netzelia (Medioli et al., 1987). Furthermore, both D. lobostoma and D. lithophila have planktonic life-stages, like many Sphaerothecina. Cucurbitella in turn, has been included into Sphaerothecina (Lahr et al., 2019) based on its round/oval-shaped test and the presence of a collar around the aperture, but classified as incertae sedis. Nevertheless, this genus shares with the genus Netzelia the ability of building a test without incorporating foreign particles (Medioli et al., 1987). Our phylogenetic tree shows (Fig. 1) that D. lithophila, D. lobostoma and Cucurbitella mespiliformis form a clade sister to the familyArcellidae, therefore we include the genus Cucurbitella with the family Netzeliidae and transfer D. lithophila and D. lobostoma to the genus Netzelia (see Supporting Information, Appendix S1).

Differential diagnosis between genera: Cucurbitella differs from Netzelia as the development of its collar creates an internal diaphragm, forming a second chamber with a central aperture (Fig. 9).