DOI 10.1111/j.1502-3931.2008.00093.x © 2008 The Authors, Journal compilation © 2008 The Lethaia Foundation LETHAIA Blackwell Publishing Ltd Microscopic evidence of serpulid affinities of the problematic fossil tube ‘Serpula’ etalensis from the Lower Jurassic of Germany OLEV VINN, MANFRED JÄGER AND KALLE KIRSIMÄE Vinn, O., Jäger, M. & Kirsimäe, K. 2008: Microscopic evidence of serpulid affinities of the problematic fossil tube ‘Serpula’ etalensis from the Lower Jurassic of Germany. Lethaia, Vol. 41, pp. 417–421 Tube structure, ultrastructure and mineralogy support serpulid affinities of the problematic worm fossil ‘Serpula’ etalensis from the Lower Jurassic of Germany. The original tube mineralogy of ‘Serpula’ etalensis is purely aragonitic and is preserved in Upper Pliensbachian specimens from eastern Germany. ‘Serpula’ etalensis represent the earliest record of aragonitic mineralogy for serpulids. The tube is formed of irregularly oriented prismatic crystals that are 3–6 μm in length and 0.5–1.0 μm in diameter. Calcitic specimens of ‘Serpula’ etalensis from Upper Sinemurian of southwestern Germany were recrystallized during the diagenesis and lack the original tube ultrastructure.  Aragonite, Jurassic, problematic fossils, Serpulidae, tube ultrastructure. Olev Vinn [olev.vinn@ut.ee], Department of Geology, University of Tartu, Vanemuise 46, 51014 Tartu, Estonia; Manfred Jäger [manfred.jaeger@holcim.com], Holcim (Baden-Württemberg) GmbH, D-72359 Dotternhausen, Germany; Kalle Kirsimäe [kalle.kirsimae@ut.ee], Department of Geology, University of Tartu, Vanemuise 46, 51014 Tartu, Estonia; manuscript received: 30/9/2007; manuscript accepted: 20/12/2007. ‘Serpula’ etalensis (Piette, 1856) is a carbonatic tubicolous fossil of probable serpulid affinities, found in the Lower Jurassic of France, Germany and England (M. Jäger, personal observation). It differs from typical serpulid tubes in terms of its regularly spaced peristomes and free unattached tube (Fig. 1A), which may have been attached to a substrate during the juvenile stage. These well-developed, closely spaced regular peristomes were probably an adaptation to the life on the surface of soft sediment, acting as anchors (Jäger 1996). The unattached tube of ‘Serpula’ etalensis somewhat resembles scaphopods and, more closely, heteromorphic ammonites (Piette 1856). Quenstedt (1856) described a similar although somewhat different species as a tentaculitid-like problematic fossil from the Jurassic of Germany. There are presumably several closely related species described under the name of ‘Serpula’ etalensis in the Lower Jurassic and the whole group needs a systematic revision (M. Jäger, personal observation). In the Triassic Period, majority of worm tubes revealed to belong to the microconchids (Taylor & Vinn 2006; O. Vinn personal observation). The Jurassic Period was a time of first major diversification of serpulid polychaetes (Parsch 1956) and one could expect a large variety of serpulid tube morphologies from that period. However, the morphologically convergent microconchids did not become extinct until the end of Middle Jurassic (Taylor & Vinn 2006; Vinn & Taylor 2007). Thus, serpulid affinities of Lower Jurassic worm tubes need a support from the data of tube structure and ultrastructure. The aim of this paper is to verify the probable serpulid affinities of ‘Serpula’ etalensis through scanning electron microscope (SEM) observations of tube structure and ultrastructure. This paper also deals with mineralogy of the tube, focusing on the effects of diagenetic changes on the tube ultrastructure and original mineralogy. Material and methods The current research comprises the following fossil material: (1) ten tube fragments from the Upper Pliensbachian of eastern Germany, from borehole ‘Barth 5/64’ near the town of Stralsund, depth is 444.4 – 446.2 m, box no. 165, sample no. 51 (Fig. 1A, B, D, E); (2) ten tube fragments from the Upper Sinemurian of southwestern Germany, from a small pit situated at the lowest point of the ‘B27’ motorway between the towns of Hechingen and Bisingen, ca. 60 kilometres southwest of Stuttgart (Fig. 1C, F, G). Examined tube fragments were ground in longitudinal and transverse direction in epoxy resin, polished and treated with a 1:1 mixture of 25% glutaraldehyde and 1% acetic acid, to which Alcian blue was added (Mutvei’s solution) for 20 min before SEM study