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 : 301

?Family Siboglinidae Caullery, 1914

‘Okukinenbetsu brown tubes’

( Fig. 9E–I )

Material. OKb4-3, larger tubes with brown walls largely obscured by rock matrix. Donated by F. Gill.

Occurrence. Okukinenbetsu River (Kanajirisawa Creek) seep carbonate, Obira-machi, north-western Hokkaido, northern Japan. Mudstone of Middle Ezo Group, Cenomanian, Cretaceous ( Majima et al. 2005; Kaim et al. 2008; Kiel et al. 2008a).

Description. Large brown silicified tubes 3.7–4.3 mm in diameter, uncompressed in section ( Fig. 9E ) and with clear multi-layering ( Fig. 9F–I ) that is very thick and well consolidated in some of the tubes ( Fig. 9I ). Highly frayed edges can be seen, suggesting that tubes were originally organic and fibrous ( Fig. 9F ).

Remarks. The clear round transverse sections of the larger brown tubes suggests that the tubes were originally rigid. Their size may indicate that the inhabitants were not frenulates, while the structure of the tube wall indicates that they are more likely to have been made by siboglinids than chaetopterids due to the thick, well-consolidated multi-layering. These tubes fall among siboglinids when more homoplasy is permitted in the cladistic analyses ( Fig. 23B ); therefore, this affinity is only tentatively suggested.

Figures

Figure 9. Cenomanian tubes from Okukinenbetsu River, Japan. A–D, ‘Okukinenbetsu yellow tubes’; A, OKb4-5, long fragment of a tube exhibiting fine longitudinal wrinkles; B, OKb4-5, short tube fragments also exhibiting fine longitudinal wrinkles; C, OKb4-4, transverse section of tube with yellowish walls; D, OKb4-2, detail of a yellow tube wall, showing some evidence of multi-layering. E–I, ‘Okukinenbetsu brown tubes’; E, OKb4, partial longitudinal and transverse sections of a tube with brown walls; F, OKb4, detail of brown-walled tube revealing a multi-layered, fibrous nature; G–I, detail of thick, multi-layered brown-walled tubes in OKb4-3 (G), OKb4-2 (H) and OKb4 (I). Scale bars: A, B = 2 mm; C, F = 300 µm; D, I = 50 µm; E = 1 mm; G = 150 µm; H = 200 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.