Lepidocoleus kuangguoduni, Gügel & Baets & Jerjen & Schuetz & Klug, 2017

Gügel, Benjamin, Baets, Kenneth De, Jerjen, Iwan, Schuetz, Philipp & Klug, Christian, 2017, A new subdisarticulated machaeridian from the Middle Devonian of China: Insights into taphonomy and taxonomy using X-ray microtomography and 3 D-analysis, Acta Palaeontologica Polonica 62 (2), pp. 237-247 : 242-245

Lepidocoleus kuangguoduni sp. nov.

Figs. 1 , 3–7 , 9 .

Etymology: Species named after Kuang Guodun, honouring his contributions to research on Paleozoic invertebrates.

Holotype: PIMUZ 32127 , part and its fragmented counterpart, over 20 sclerites.

Type locality: 500 m E of the village Napiao and about 1 km NW of Luofuxiang, NW Guangxi, China .

Type horizon: Tentaculite claystone with the trilobite Ductina vietnamica, Eifelian, Nandan Formation, Middle Devonian.

Diagnosis.— Lepidocoleus with presumably a low number of sclerites (around 22). The slightly alternating sclerites are elongated dorsoventrally with pronounced anterior and posteriorly projecting points as well as an arched dorsal edge. The width of the dorsal depression is about one third of the entire width of the scleritome. Density of rugae is ca. 9–11 per mm with about 40 rugae per sclerite. Estimated length of the animal is around 20 mm.

Description.—The holotype and only specimen PIMUZ 32127 is a slightly disarticulated specimen with remains of over 20 sclerites. The sclerite-bearing patch is about 15 mm long, about 10 mm wide, and about 3 mm thick. The original skeletal material has been dissolved diagenetically and partially, the voids had been filled by limonite (likely primarily pyrite) and partially, the voids are empty, thus providing a reasonable density contrast for CT-scanning. The number of sclerites preserved indicates that each side had more than 10 sclerites per side.

In terms of number of sclerites per side, we presume that not many are missing due to the fact that so many sclerites are still in place and there are no signs for scattering due to currents. Additionally, no sclerites were seen around that patch. We thus suggest that this species had probably 22 sclerites.

The sclerites range between 2.5 and 2.9 mm in length (anterior-posterior), between 2.1 and 3.2 mm in height (dorsoventral) and between 1.0 and 1.5 mm in width (lateral). The depression in the dorsal hinge is 0.5 to 0.6 mm wide and 0.2 to 0.4 mm deep. The outline of the sclerites in lateral view ranges from subtrapezoidal (sclerite 7) via subtriangular (sclerite 6) to subrectangular (sclerite 1), but this might partially be due to incompleteness. The dorsal margins are quite strongly vaulted with the midpoint being 0.2 mm higher than the anterior and posterior edges in sclerite 2 (at a sclerite length of 2.7 mm). The anterior and posterior edges are slightly concave, with the edges being more strongly bent dorsally. This is linked with the presence of anterior and posterior processes at the margin of the dorsal depression.

The 3D-prints allowed the reconstruction of the dorsal depression, which has a width ratio of ca. 0.3 of depression width to articulated scleritome width when closed. The lateral edge of the dorsal depression is gently sinusoidally bent and visible in dorsal view ( Fig. 4 ). Heeding this viewing direction, the overlapping part of the sclerite becomes wider anteriorly. The concave part of the dorsal depression of the sclerites is subtriangular to subtrapezoidal and tapering posteriorly ( Fig. 4 ).

The rugae are discernible both optically and in the reconstructions based on the CT-image stack. At the ventral margin, sclerites 1 and 5 bear about 10 horizontal rugae on 1 mm, so the spacing appears to more or less uniform in the sclerites of both sides.

The exact position of the single sclerites is difficult to determine; none of the better preserved ones can be assigned unequivocally as being a terminal sclerite of either end. Nevertheless, the more subrectangular sclerites such as sclerites 1 and 2 likely belong rather to the middle of the tube while strongly tapering morphologies with pronounced differences in length between the anterior and posterior edges probably derive from one of the ends of the tube. Consequently, sclerite 5 was presumably positioned close to the posterior end of the tube. Due to its low overall height, we suggest that sclerite 7 might derive from near the anterior end.

Remarks.—Most members of the genus are clearly older, i.e., Silurian or Ordovician. Important characters apparently are the number of sclerites, the outline of the sclerites and the dimension of the dorsal furrow. Rugae spacing appears to be at least partially controlled by ecological factors as it is often quite irregular. The outline varies slightly through ontogeny as inferred from the course of rugae.

As discussed above, the number of sclerites of the new species might be as low as in Lepidocoleus britannicus , L. hohensteini , L. jamesi , and L. sarlei (see also Fig. 9 ). Its sclerite outline differs from most other known species in the elongate, often subtrapezoidal shape with anterior and posterior processes. Among all species, L. sarlei has the most similar sclerites, but even here, differences are evident such as the stronger dorsal arching and the longer anterior and posterior processes in the new species. As far as the dorsal furrow is concerned, it is again L. sarlei that is morphologically the closest: Both L. sarlei and L. kuangguoduni sp. nov. have a broad dorsal depression (width ratio of ca. 0.35 in L. sarlei and ca. 0.3 L. kuangguoduni sp. nov) with alternating left and right sclerites.

Stratigraphic and geographic range.— Type locality and horizon only.

A B C D E

Figures

Fig. 1. Machaeridian annelid Lepido- coleus kuangguoduni sp. nov., Nandan Formation, Eifelian, near Napiao, Guangxi (China). A. The main plate containing most machaeridian scler- ites. B. The counterplate of the same specimen (it was glued back onto the slab prior to CT-scanning); note the limonitic filling of the rugae and the chaotic arrangement of the plates.

Fig. 3. Overview over the assemblage of the sixteen 3D-objects which were created from different viewpoints. Orthographic top (A) and front (B) views. Orthographic top view (C), projected on the sample to show the position of the 3D-model in the correct position on the x-y-plane and corresponding viewing directions. Orthographic left side (D) and right side (E) views.

Fig. 4. Overview of the almost complete sclerites from the 3D-analysis (orthographic perspective). Group I: sclerites 1, 4, 6 (A–C) and group II: sclerites 2, 5, 7, 10 (D–G). Internal (A1–G1), lateral (A2–G2), dorsal (A3–G3), posterior (A4–G4), and anterior (A5–G5) views.

Fig. 5. Overview of the other objects found in the sample. A. Object 3 could not be identified with certainty, but is likely part of a sclerite from the flank. B. Sclerite 9 might be from the dorsal articulation. C. Objects 15 and 16 might belong to the same, incomplete sclerite. D. Sclerite 11 preserves only the dorsal flange. E. Objects 8, 12, 13, and 14 might actually be parts of two sclerites as indicated by the white lines.

Fig. 6. View of a pair of 3D-prints of articulated right (1) and left (2) sclerites from obliquely posterior (A) and dorsal (B) views. Note the perfect fit of the sclerites. Within the hinge of sclerite 1 in B, the indentation on the right of the hinge flange is an artefact from tresholding (probably, the shell was too thin in that place). Sclerites 1 and 2 were enlarged 25 times (for original dimensions see Fig. 4).

Fig. 7. Overview of objects interpreted as dacryoconarids surrounding the machaeridian sclerites. A. All objects including the ones discarded for further analysis (light grey). B. Dacryoconarids selected for measurements (red).

Fig. 9. Comparison between the known species of Lepidocoleus and L. kuangguoduni sp. nov. with number of sclerites, age, and geographic occurrence indicated; lateral (A) and dorsal (E) views of the fossils, images of sclerites (B), outlines of sclerites (C), cross sections, to show the proportions of the dorsal depression (D).