Dear Marcus: Your Mystery rad that you just have posted is something that I have not seen before, not in my material nor in the literature! However, in her book, Petrushevskaya (1981) do give some line-drawings that can be related to your bug, and I am referring you to her pp. 63-70. The following text has been translated here in Oslo, and I ask colleagues who are competent in both English and Russian to compare this English translation with the original Russian text. Please report back if something is wrongly translated!!! Could you look through the two genera below and see if you agree to one of the two, or none of them?
1.Subfamily CLATHROMITRINAE Petrushevskaja, 1971
Clathromitrinae Petrushevskaya, 1971 "b" :69.
Clathromitridae with developed porous or netted wall of the shell (see above). The spicules D and L are directed down in the curved way, they are often slightly curved.
8.Genus Clathromitra Haeckel, 1881, sensu Petrushevskaja, 1971 "b" (fig. 29).
Clathromitra Haeckel, 1881:432, 1887:1218; Petrushevskaja, 1971 "b":71. Type species - Cl.pterophormis Haeckel, 1887, pl.57, figure 8 ("Chall.", 265, center of Pacific, sediments) - according to the following terminology (Campbell, 1954:122).
Clathromitrinae with the subconical, porous cephalis. The pores have different shape and size, irregular distribution.
Usually there are ridges and callosities on the external pole which divide the wall into separated parts often convex or concave. They form subdivisions of the general wall of the shell. Sometimes a similarity of the spongy layer is developed. The wall of the cephalis becomes the wall of the thorax without any external border. The thorax is shorter than the cephalis. Three "feet" are included in the walls of the thorax; they are usually shorter than the apical horn. The horn and "feet" are flat, cut. The edges are connected to the wall by additional appendages. 2 or 3 porous poles are located around the apical horn. The spicule A, perpendicular to MB passes like a pillar, the appendages and start from the middle part of the cephalis. The spicule Vert is directed up in a curved way and externally forms a small horn. The spicules D and L form the lateral appendages inside of the shell which perform the walls. The spicules l are not developed. The branched axobate often is well developed.
Cenozoic. All latitudes. Seldom. Cl. pentacantha Haeckel, 1887.
12.Genus Verticillata Popofsky, 1913 (fig.33).
Verticillata Popofsky, 1913:281 - Verticellata Campbell, 1954:104. Type species - V.hexacantha Popofsky, 1913, Text fig.11 (South Atlantic, plankton) - according to monotypy.
Clathromitrynae - dome(copula)-like the cephalis becomes a tube of the apical horn, which has small pores. It differs from Clathromitra in having the small pores in the thin wall of the cephalis. The internal structure is similar to Clathromitra described here. According to figure drawn by Popofsky it differs because the spine A is not perpendicular to MB but is directed a little forward. There are a lot of lateral appendages situate on the spicules A, D, L, which are founded also in Clathromitra..
In Clathromitra these appendages are included in the external, porous poles and form the bars between pores, but in Verticillata the appendages inside support the porous wall, which covers not only the base volume of the cephalis but also apical horn and "feet", and form tubes around the "feet". The thorax is very short, not separated from the cephalis.
? - present. Temperate latitudes.
Seldom. Likely Pteroscenium arcuatum. Haeckel, 1887.
Kjel R. Bjørklund
Sorry, I forgot to write a blurb to go with the previous comment and name. The pictured species appears to be a form I described as Lithomelissa ? sakaii in Micropaleontology 46(3) pp.189-228. Unfortunately the publishers got names mixed up in the Text-Fiures so the genus in the caption of Text-Figure 9 should be Lithomelissa, not Plannapus. I found a lot of these in strewn slides, but when I searched the residues for specimens to SEM I couldn't find any, and I didn't have the time to process any new material, hence no SEM pictures in the paper.