Bundenbachochaeta eschenbachensis (Bartels and Blind, 1995)


Diagnosis. Body elongate, oval; 15 to more than 20 parapodia-bearing segments – notopodia and neuropodia differ in the length and number of chaetae (c. 40 and c. 10, respectively). Acicula stout. Prostomium rounded with a pair of short stout appendages. (After Bartels and Blind 1995.)

Geological horizons and locality. Eschenbach Member (holotype) and overlying Wingertshell Member (additional specimens) of the Kaub Formation, Obereschenbach Quarry, Bundenbach.

Holotype. DBM:HS 717

Description. All specimens are somewhat flattened in parallel aspect. The worm is bilaterally symmetrical and elongate, tapering both anteriorly and posteriorly from a maximum width at about the mid-length, so it is also symmetrical about this point. The four complete specimens are 19 mm long (2 mm wide to the base of the parapodia, 11% of length), 46 mm long (Text-fig. 2C, NM:PWL 2002/222-LS, 7 mm wide, 15% of length), 48 mm long (Text-fig. 1, DBM:HS 717: 8 mm wide, 17% of length), and c. 100 mm long (Text-fig. 2A, B, DBM:HS 736: 23 mm wide, 23% of length). Thus, the width increases relative to length in larger individuals.

The holotype (Text-fig. 1; Bartels and Blind 1995) is the best-preserved specimen. The side of the worm exposed cannot be determined with confidence, but it is assumed to be the ventral (and left and right are designated accordingly below). The anterior part of the head is heavily pyritized (as it is in NM:PWL 2002/222-LS, Text-fig. 2C). The structure is not clear, but appears to show traces of two appendages, perhaps palps or antennae; there is no evidence of jaws. The trunk bears c. 20 pairs of parapodia. Those on the right appear to be offset slightly posteriorly (Text-fig. 1C). The parapodia are clearly biramous as evidenced by well-preserved examples anterior of the mid-length on the right side and more posteriorly on the left (Text-fig. 1). The ventral ramus of the parapodia (neuropodium) bears longer more robust chaetae; c. 10 are evident, which are near parallel. They are <10% of the total length of the body. The dorsal ramus (notopodium) bears more delicate chaetae, c. 40 in number, which diverge strongly and are attached over a wider distance. They appear shorter than the chaetae of the ventral ramus in the anterior left parapodia (the difference perhaps exaggerated by preparation) but are more similar in length in the posterior right. The X-radiograph shows strongly pyritized linear structures, particularly on the left side, which extend beyond the proximal part of the parapodia (Text-fig. 1B). At least two per parapodium are evident in some cases. These structures are interpreted as aciculae (Text-fig. 1C). Both chaetae and aciculae are fragmented along their length (Text-fig. 1C), but this is a taphonomic artefact reflecting the nature of pyritization. The trunk terminates in a bifid structure (which does not appear to be made up of parapodia) which may represent a pygidium. A linear structure about the mid-length may represent part of the gut trace (Text-fig. 1A, C).

The largest specimen, DBM:HS 736, is assumed to afford a dorsal view (Text-fig. 2A, B). It preserves evidence of 17 pairs of parapodia (there were presumably more), solely as the pyritized remains of the chaetae. The ramus bearing the large number of more slender chaetae is preserved uppermost. The soft tissues of the head and trunk have been lost, presumably through decay. The central area preserves a network of pyritized burrows, some of them revealed in the X-radiograph (Text-fig. 2B), which extend beyond the posterior of the trunk, perhaps representing the activities of a scavenger. The smallest specimen, DBM:HS 597 (Text-fig. 2D), shows evidence of c. 15 pairs of parapodia and presumably represents a juvenile. Only the notopodia appear to be preserved. The nature of the linear structures flanking the trunk axis is unknown, but they may represent longitudinal muscle bands. There are structures at the anterior that are difficult to interpret and might represent jaws or other head appendages.