Tubulohyalichnus McLoughlin et Furnes, 2009

Microboring; substrate siliceous; tracemaker bacterium

Category of architectural design: 2.59. Cylindrical vertical to oblique borings.

Unbranched, cylindrical.

Diagnosis. Tubular structures that radiate away from fractures, vesicle walls and inwards from the margins of volcanic glass fragments. Tubes range in diameter between c. 0.4
m and c. 6
m with an average diameter of 1.4
m and the mineralized tubes being higher in this range (data presented by Furnes et al. 2007, fig. 6). Their lengths are highly variable, from a few microns to several hundred microns, with only limited variation in diameters along their lengths. Tubes may be straight, curved, branched or helical, and may exhibit annulations along their walls. They occur as isolated tubes or dense clusters of subparallel tubes that may be hollow, partially or wholly infilled with mineral phase(s).

Differential diagnosis. Extended tubular structures that propagate away from fresh surfaces along fractures, vesicle walls and the rims of volcanic glass fragments. They can be distinguished from Granulohyalichnus igen. nov. by their much greater length-towidth ratio. Tubulohyalichnus igen. nov. is comparable with the ichnogenus Fascichnus ispp. found in carbonate substrates (Radtke & Golubic 2005), which is produced by cyanobacteria, and, in particular, ichnotaxa such as Fasciculus dactylus, first described by Radtke (1991). This trace is characterized by a carpet or radiating bundle of tubes up to 150
m long and 3–8
m in diameter that show only rare bifurcations (e.g. Wisshak et al. 2005, fig. 6A). These tubes are of constant diameter except sometimes for slight thickening seen towards their distal ends. This ichnotaxon is known to be produced homeomorphologically and at least three cyanobacteria species are capable of forming this trace (see Wisshak et al. 2005).