Friday, 8 January 2016

Possible Annelid Worm tubes from the Early Devonian of Brazil.

Worm tubes first appear in the fossil record in the Ediacaran and become increasingly common through the Palaeozoic. Most Worm tubes today are made by Polychaete Annelids, a group which have existed since at least the Cambrian, however in the Palaeozoic a variety of other groups, such as Tentaculitoids (thought to have been related to Molluscs and Lophophorates) and Hyolithelminths (possibly Cnidarians) are known to have made tubular structures, making it difficult to assess when tube-building Polychaetes first appeared.

In a paper published in the journal Acta Palaeontologica Electronica on 21 December 2015, Olev Vinn of the Department of Geology at the University of Tartu, Carolina Zabini and Gustavo Sene-Silva of the Universidade Tecnológica Federal do Paraná, Kalle Kirsimäe also of the Department of Geology at the University of Tartu and Lara Susan-Marcos, also of the Universidade Tecnológica Federal do Paraná, describe a series of tubes from the Early Devonian Ponta Grossa Formation of Paraná State in Brazil.

The tubes are fragmentary and have been reworked prior to preservation in sediment, The sample examined contains about 50 such tubes with a maximum length of 2.5 cm. They are 2.9–5.8 mm in width and eliptical, though this is thought to be due to compression. They are banded, with seven-to-ten rings every 5 mm, and do not taper or branch. Vinn et al. describe these as Annulitubus mutveii, where 'Annulitubus' means 'ringed-tube' and 'mutveii' honours palaeontologist Harry Mutvei for his work on the skeletal structures of extinct invertebrates.

Sample (MN 9571-I) from Rio Caniú outcrop, Ponta Grossa Formation, Upper Emsian, Lower Devonian. (A) Fragment showing numerous tubes; holotype of Annulitubus mutveii  (MN 9571-Ia) and paratypes (MN 9571-Ib–e). Note that all tube fragments are straight and have similar orientation, some show smooth surfaces, with very subtle striae, in others it is possible to see shallow rings. (B) Enlarged holotype (MN 9571-Ia), note the smooth rings. (C) Fragment showing paratype (MN 9571-Ig). Vinn et al. (2015).

The Worms are interpreted as having grown close to the site of deposition, probably in dense clusters but not attached to one-another. The locality is not thought to have had any solid rock close by, but shells were available and could possibly have served as points of attachment, or the worms could have lived and formed tubes partially or wholey within the sediment. The tubes are preserved in silica, a mineral not known to have been used to make tubes by any Worm group, and therefore Vinn et al. interpret this as a secondary material which has replaced the original tube material. Silica requires very alkaline conditions to form, conditions under which calcite tubes would be expected to lose much of their original structure, leading Vinn et al. to suggest that the tubes were originally formed from organic material rather than mineral. Such a structure, with non-tapering, non-branching organic tubes with a banded structure is typical of several Polychaete groups, but not associated with any non-Polychaete group, leading Vinn et al. to conclude the tube-builder was almost certainly a Polychaete.

See also... lizae: A new species of Ampharetid Worm from Lizard Island on Australia's Great Barrier Reef.               Ampharetid Worms are small, usually marine, Annelid Worms related to the tube-building Trumpet Worms... Bone-eating Worms from England.                                                 Siboglinid Worms are a distinctive group of Annelids which lack mouths and digestive tracts in their... new species of Serpulid Worm from the Caribbean.                                                 Serpulids are distinctive Polychaete Worms found throughout the world’s oceans, from the intertidal zones to the deep seas. They live in calcareous tubes, which they cement to hard substrates, and are...
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