A Question And Perhaps A Puzzle

I have a question for the geo- and paleo-minded folks out there:

How deep can a benthic diatom burrow?

Now the reason I ask this question is that the worm Paraonis makes spiral burrows (pictured above) that have been identified as "traps" for diatoms (Minter et al, 2006). This means that the diatoms must be able to burrow to at least the depth that the sprials are produced but I have read that diatoms have only been identified as burrowing up to 3 mm (which is a big deal for such a small creature) (Hay et al, 1993) but Paraonis burrows have been identified up to 10 cm down (Risk and Tunnicliffe, 1978). Quite a contrast.

This means that either they are wrong (this is not a diatom trap), they are eating other things (which they don't think so), or diatoms are burrowing deeper than I can find literature on.

So I was wondering if anyone has any knowledge of diatom burrowing depths. If you do please comment or send me an email.

Hay, S.I., Maitland, T.C., & Paterson, D.M., 1993, The speed of diatom migration through natural and artificial substrata: Diatom Research, v. 8, p. 371-384.

Minter, N.J., Buatois, L.A., Lucas, S.G., Braddy, S.J., & Smith, J.A., 2006, Spiral-shaped graphoglyptids from an Early Permian intertidal flat: Geology, v. 34, p. 1057-1060.

Risk, M.J., & Tunnicliffe, V.J., 1978, Intertidal spiral burrows; Paraonis fulgens and Spiophanes wigleyi in the Minas Basin, Bay of Fundy: JOURNAL OF SEDIMENTARY RESEARCH, v. 48, p. 1287-1292.