Bithekammina Silva, Gooday, Pearse & Cunha, 2011, gen. nov.

Bithekammina gen. nov.

The systematic division of higher taxa based on morphology has little support from molecular studies (Pawlowski et al. 2002). We therefore recognise the family Saccamminidae only in order to provide a systematic context for our new taxa that is consistent with previous studies.

Etymology. The first part of the name (the suffix bi) means two; the middle part (theka) derives from the Greek theke (θηκη) meaning case or test; the last part (-ammina) is a common ending for generic names of agglutinating foraminiferans and is derived from the Greek word ammos (αμμος), meaning sand.

Type species. Bithekammina occulta Aranda da Silva and Gooday

Diagnosis. Test free, monothalamous, spherical to ovate in shape, and generally 200–400 µm in size. Test surface very smooth, translucent with diffuse silvery highlighted in reflected light. Single aperture forms round opening with slightly raised rim but otherwise without any associated structures. Wall thin and composed largely of tiny (usually 1–2 µm) plate-like clay particles overlying organic lining. Cell body with large nucleus, but without any other obvious inclusions. Test typically enclosed within larger, more coarsely agglutinated case (‘secondary test’), which gives rise to long, narrow tubular extension that corresponds to the aperture of the primary test.

Remarks. The most interesting characteristic of Bithekammina is the fact that the test is enclosed in an outer agglutinated case, a feature not present in any other named ‘saccamminid’. The test itself resembles that of the newly-described genus Niveus Altin, Habura & Goldstein 2009 (type species N. flexilis) in being rather small, flexible and ovate in shape with an outer surface composed of tiny, flake-like clay particles. In N. flexilis, however, these particles overlie a much thicker inner organic lining, so that the test appears to have an organic wall when viewed under a dissecting microscope. The organic lining is thin in our new genus and the wall is separated from the cell body by what appears to be an open space, which is wider near the distal end than the proximal end. Another recently described ‘saccamminid’ genus, Leptammina Cedhagen, Gooday & Pawlowski 2009 (type species L. flavofusca), is much larger (up to 2 mm diameter) than Bithekammina and has a thicker test wall. It also has a clearly developed endosolenial tube, a feature absent in Bithekammina.

Apart from the presence of a secondary agglutinated case, Bithekammina differs from Ovammina (type species O. opaca Dahlgren, 1962) in having an oval rather than egg-shaped to fusiform shape, a much thinner and more finely agglutinated test wall, and in lacking a well-developed endosolenial tube.