Siboglinidae Caullery, 1914

Georgieva, Magdalena N., Little, Crispin T. S., Watson, Jonathan S., Sephton, Mark A., Ball, Alexander D. & Glover, Adrian G., 2019, Identification of fossil worm tubes from Phanerozoic hydrothermal vents and cold seeps, Journal of Systematic Palaeontology 17 (4), pp. 287-329 : 296-297

?Family Siboglinidae Caullery, 1914

‘Murdock Creek tubes’

( Fig. 5 )

Material. WA-MC LACMIP loc. 6295, one spiralling tube ( Fig. 5A ), another tube with a ~ 90 º bend, and a smaller tube observed in thin section only. Donated by J. L. Goedert.

Occurrence. Murdock Creek, Clallam County, Washington State, USA (~ 48 º 9 ' N, 123 º 52 ' W). Loose seep carbonate blocks. Pysht Formation, late Early Oligocene ( Goedert & Squires 1993; Kiel & Amano 2013; Vinn et al. 2013).

Description. Carbonate tubes 0.7–3.0 mm in diameter, appearing non-branched, non-agglutinated and nontapering in the tube fragments observed. The spiralling tube ( Fig. 5A ) appears to have coarse longitudinal wrinkles on its surface, but whether these are original is uncertain. In thin section, tube walls are thick and concentrically multi-layered ( Fig. 5B–D ), and occasionally delaminated ( Fig. 5B ). Some of the tubes appear to have originally been flexible ( Fig. 5C ) and to have had fibrous walls due to visible preserved wall tears in thin section ( Fig. 5D ).

Remarks. These tubes appear to have been organic originally due to preserved tube wall tears that reveal a fibrous nature. The size of the tubes, their thick, multi-layered walls and the spiralling that they exhibit suggest that the tubes may have been made by vestimentiferans, as the combination of these features are not commonly encountered in other organic tube-building annelids that occur at vents and seeps. Due to a limited amount of material available for study, and as these tubes were only resolved among those of siboglinids when homoplastic characters are downweighted less within cladistic analyses ( Fig. 23B ), the tubes are only tentatively assigned to the siboglinids.

Figures

Figure 5. ‘Murdock Creek tubes’, WA-MC LACMIP loc. 6295, Early Oligocene, Washington State, USA. A, a single tube in hand specimen possibly bearing longitudinal wrinkles. B, detail of tube wall in transverse section with thick, multi-layered and delaminated tube wall. C, transverse section of tube which appears to have originally been flexible. D, detail of tube wall where a preserved tear occurs, revealing fibre endings (grey arrow). Scale bars: A = 5 mm; B = 150 µm; C = 100 µm; D = 50 µm.

Figure 23. Strict consensus cladograms constructed using a total of 64 modern and fossil annelid taxa and 48 mostly morphological tube characters. Analyses were performed using implied character weighting, with the concavity constant set as default (k = 3; A), and also set to downweight homoplastic characters less (k = 4; B). Numbers on nodes represent groups present/contradicted support values. Modern taxa are coloured according to taxonomic groups; fossil taxa are in grey. A, consensus of 271 most parsimonious trees (best score = 15.387, consistency index = 0.195, retention index = 0.264); B, consensus of 60 most parsimonious trees (best score = 13.568, consistency index = 0.232, retention index = 0.569). Symbols/colours indicate taxonomic affinities.