Hallucigenia, Conway Morris, 1977
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publication ID |
https://doi.org/10.1186/s13358-025-00381-6 |
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persistent identifier |
https://treatment.plazi.org/id/03E687FC-2205-FFC5-FF6C-902D0399FE3E |
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treatment provided by |
Felipe |
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scientific name |
Hallucigenia |
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Hallucigenia ? sp.
Figure 3 View Fig
Material. — One specimen, part and counterpart. Jince Formation (upper Wuliuan, Miaolingian Series ), Acadolenus snajdri Biozone , hill slope of Vinice near Jince (outcrop 5 of Fatka & Szabad, 2014), Příbram–Jince Basin. Held in the National Museum , Prague, under catalogue number NM-L 40847 .
Preservation. —Te nearly complete specimen is preserved as dark carbonaceous compressions (part and counterpart) in weathered, light-brownish-grey fine greywacke. Te specimen is flattened, with slightly oblique lateral compaction.
Description. —Te specimen consists of a large part of the trunk with remains of the ventral appendages and dorsal spines. Te preserved part of the trunk is 19.05 mm long and up to 1.4 mm wide. Te interpreted anterior end of the specimen is incompletely preserved; a curved, slightly darker line could mark the outline of the head region (?HR in Fig. 3B View Fig ), defining the anterior–posterior orientation of the trunk. Tree incomplete and poorly outlined darker spots in the area between the inferred anterior region and the trunk most probably represent the remains of two pairs (?) of frontal appendages (FA in Fig. 3B View Fig ). On the interpreted ventral surface of the trunk, at least 22 long lobe-like appendages are preserved (4–25 in Fig. 3B View Fig ). Some of these appendages seem to be arranged in pairs (e.g. 8/9, 14/15, 16/18, 24/ 25 in Fig. 3B View Fig ). Te longest appendages are 8–9 mm long (appendage numbers 8, 13 – 15, 18, and 20 in Fig. 3B View Fig ); no terminal claw is seen. No trace of annulation is visible on the appendages or the trunk. Te inferred dorsal surface of the trunk bears at least 12 outgrowths interpreted as dorsal spines. Some of these spines seem to be organised in pairs (e.g. 2/3, 4/5, 6/7, 9/ 10 in Fig. 3B View Fig ).
Discussion. —Compared to material from well-studied Lagerstätten (such as the Burgess Shale, Chengjiang, Kaili, or Spence Shale), the Czech specimen is rather poorly preserved. Although the outline and the overall morphology are preserved, many details that could aid in the taxonomic classification of the specimen are missing. Te general size and proportions of the Jince Formation specimen correspond closely to some previously described specimens of Hallucigenia (cf. Figure 1 C View Fig of Caron et al., 2013), although the interpreted appendages and spines are more slender relative to the body than in previously described material. However, given the organic composition of the specimen, its general morphology, and size, alternative interpretations require further consideration; specifically, pterobranch, hydroid, and alga.
Tere is a relatively robust record of pterobranchs from Miaolingian strata ( Maletz, 2024), including from other stratigraphic levels within the Teplá-Barrandian Unit ( Maletz et al., 2005). However, the strongly asymmetric distribution and perpendicular onset of the “outgrowths”, interpreted herein as lobopods and spines, do not fit well with a pterobranch interpretation of the specimen (cf. Figure 4 A View Fig of Maletz, 2024). Te specimen does not correspond well to any known Miaolingian pterobranch (cf. Maletz, 2024). Te same argument can be applied to reject a hydroid interpretation of the specimen (cf., e.g. Song et al., 2021)—the distribution of “outgrowths” and their angle relative to the “main axes” make it difficult to accommodate a hydroid interpretation.
Considering an algal affinity, the macrofossil specimen is indeed broadly comparable to some stoloniform and/or monopodial macroalgae (sensu LoDuca et al., 2017). Te fossil record of both groups in the Cambrian is, however, very limited, and they only became more common in the Ordovician ( Bykova et al., 2020; LoDuca et al., 2017). Te only Cambrian member of the stoloniform macroalgae is Parallelphyton Wu & Zhao in Wu et al., 2011. However, Parallelphyton differs substantially from the Jince specimen in its general morphology, with closely bundled, uniformly oriented trichomes that are not dispersed along the entire axis. Te fossil record of monopodial macroalgae is also very limited in the Cambrian ( LoDuca et al., 2017). Notably in this regard, the lobopodian Acinocricus was initially compared to charophyte algae (see Conway Morris & Robison, 1988). Although possible charophyte-sourced cryptospores are known from Cambrian strata ( Strother & Foster, 2021), a macrofossil record of charophytes is only present from Silurian onwards ( Martín-Closas & Soulié-Märsche, 2015).
Given the morphology of the macrofossil specimen, the presence of lobopodian microfossils in the Jince Formation, and the demonstrable incongruence with other explanations, we tentatively describe the specimen as a lobopodian and identify it as Hallucigenia ? sp.
Caron et al. (2013) concluded that hallucigeniid spines were rigid but flexible with a variable degree of phosphatic mineralisation; however, lobopodian SSFs were likely secondarily mineralised, as suggested by Slater et al. (2018). Te lack of phosphatic components in SCFs cannot be explained by loss during laboratory treatment, because the HF-only treatment utilised in most SCF studies can preserve originally phosphatic microfossils ( Kovář et al., 2024). Spines in macrofossil remains of Hallucigenia contain only a limited amount of phosphorus ( Caron et al., 2013). In the Jince specimen, two of the structures interpreted as spines appear slightly bent (spines 7 and 10 in Fig. 3B View Fig ) further suggesting little to no primary mineralization.
All three known species of Hallucigenia bear fourteen dorsal spines organised in seven pairs; at least 12 spines appear to be present in the Jince specimen (see Fig. 3 View Fig ). Te number of lobopods in the Czech specimen is also noteworthy; the minimum of eleven pairs of lobopods exceeds the known number reported in earlier described species of Hallucigenia ( Conway Morris, 1977; Hou & Bergström, 1995; Steiner et al., 2012), thus also disagreeing with the original definition of Hallucigeniidae ( Conway Morris, 1977) ; however, the number would fit the redefinition of Hallucigeniidae by Caron and Aria (2017). Further material will be necessary to ascertain whether the Bohemian specimen could be accommodated within Hallucigenia , or whether establishing a new genus would be appropriate.
It would be challenging to ascertain whether the SCFs recovered from the O. hybridus Biozone originate from the same taxon as the Jince Formation macrofossil lobopod specimen. Caron et al. (2013) compared isolated sclerites similar to the specimens herein with individual species of Hallucigenia ; however, other lobopodian taxa, of both hallucigeniids and luolishaniids, also bear spines with a cone-in-cone structure, similar surface ornamentation (even though generally not figured in detail), and a comparable size range ( Caron & Aria, 2017, 2020; Yang et al., 2015).
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