taxonID	type	description	language	source
080373171C49FFC4FC63F9C9FE95E86F.taxon	description	Figures 2 - 7 Description. Simple tusk-like curved tubes, expanding towards aperture, typically 1 - 2 mm in diameter, up to 15 mm in length. A notable swelling of the tube is commonly developed at the apertural end. Two distinct layers are clearly observed (Figure 2). The tube has a chevron-shaped growth lamellae passing through both the major layers (Figure 2). In the inner layer the chevron is vertical to ‘ C’ - shaped, whereas in the outer layer it continues at an angle of approximately 10 ˚ from the interface between the two layers. The outer layer comprises regularly ridged prismatic crystals (RRP) (Figures 3 - 5), arranged approximately perpendicular to growth lines. Crystals have a typical width of 1.54 to 5.88 µm, by up to 300 µm in length (the thickness of the layer), with a distinct parallel ridge and groove texture on the outer surface of the crystals. Ridges and grooves in the order of 23 to 155 nm wide. Ridge and grooves on adjacent crystal faces (within a single crystal) are arranged in a V-shaped pattern (in which the ‘ V’ points towards the interior of the tube). Organic matter rarely observed between crystals (Figure 3 B, D). Cross-sections of the crystals form a range of triangular, wedge-shaped, polygonal to more irregular shapes (Figure 4), with margins marked by peglike facets (Figure 4), that mark the position of surface ridges and grooves. Pegs range from tightly to loosely interlocking (Figure 4 F). One cross-section illustrates internal structure, comprising 500 - 700 nm euhedral, zoned crystals (Figure 6 A, B). Transverse breaks appear smooth, though closer examination shows that they often display irregular stepped conchoidal fractures, and that these surfaces have a rough undulating nature, with structure in the sub-micron range (Figure 5). Other crystals broken along their length have an apparent ‘ laminated’ structure approximately perpendicular to the crystal long axis (Figures 3, 5), although some breaks illustrate that these are divided into micron-sized packages that are strongly inclined to the tube surface (Figures 3 B, 5 D, E). The interface between the outer and inner layers is sharply defined (Figures 2, 6 C, D), with the regular ridged prismatic (RRP) crystals each initiating from a single point locus (Figure 6 D). The inner layer comprises long thin acicular crystals, with polygonal, occasionally observed as hexagonal, cross-section, typically 94 to 393 nm by ~ 1.5 µm to 11.5 µm. Along the inner tube surface crystals are roughly parallel to the circumference of the lumen (Figure 7 A), perpendicular to the tube long axis, and appear to occur in loose bundles, angled at up to 10 ˚ to the line of the tube circumference (Figure 7 B, C). In addition, transverse sections across tubes illustrate similar groupings and orientations (Figure 7 D, E). Both the latter have a “ woven ” appearance (Figures 7 A-D, 8). In the longitudinal section, this layer has a ‘ granular’ appearance (Figures 7 F-H, 8). The outer layer is typically four or five times as thick as the inner layer. Composition. Powder XRD analysis indicates the occurrence of calcite, with a d 104 spacing of between 3.02 - 3.04 (Figure 9), which equates to approximately 4 - 10 mol % MgCO 3 (see Goldsmith and Graf 1958, table 5). EDX analysis of selected areas (approximately 50 µm 2) indicates that the inner layer has a higher Mg content (Ca: Mg ratio ~ 15: 1 to 19: 1) compared to the RRP layer (21: 1 to 30: 1).	en	Buckman, James O. (2020): The tube of Ditrupa bartonensis (Annelida, Serpulidae), from the Eocene of southern England: Observations on microstructure and its significance. Palaeontologia Electronica (a 37) 23 (2): 1-13, DOI: 10.26879/1098, URL: http://dx.doi.org/10.26879/1098
