?Family Siboglinidae Caullery, 1914

‘West Fork Satsop River tubes’

(Fig. 4)

Material. JLG459C, WFSR-3B, several wavy tubes. WFSR-3A-1, several tubes observed in thin section. Donated by J. L. Goedert.

Occurrence. West Fork Satsop River, Grays Harbor County, Washington State, USA (~ 47 º 16 ' N, 123 º 33 ' W). Float seep limestone blocks. Lincoln Creek Formation, Oligocene (Campbell & Bottjer 1993; Kiel & Amano 2013).

Description. Carbonate tubes up to 2.4 mm in diameter, somewhat sinuous, non-branching, and not appearing to have been agglutinated or to taper in the observed fragments (Fig. 4A, B). Tubes appear inflexible and unattached, and the tube walls are free of ornamentation. In thin section, the tube walls are brown, of variable thickness but finely multi-layered (Fig. 4C, D). An originally organic composition of the tube walls is also supported by confocal microscopy (Fig. 25), and breaks in the tube wall can be observed showing potential frayed fibre endings (Fig. 4D).

Remarks. These tubes were resolved only within the cladistic analysis that allowed for more homoplasy (Fig. 23B), in which they fall among siboglinids. The fibrous organic composition and concentrically multi-layered walls are, however, also consistent with the tubes of chaetopterids, although the smooth walls and sinuosity of these tubes suggest that they are possibly more likely to have been made by siboglinids. We therefore tentatively suggest a siboglinid affinity.