Jianfengia, Hou, 1987
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publication ID |
https://doi.org/10.1038/s41467-025-62849-w |
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DOI |
https://doi.org/10.5281/zenodo.17038458 |
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persistent identifier |
https://treatment.plazi.org/id/D864325A-597B-0354-7C1C-4A726641F960 |
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treatment provided by |
Julia |
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scientific name |
Jianfengia |
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External attributes and diagnostic traits
Two Jianfengia specimens of similar size, YKLP11117 ( Fig. 1a – e View Fig ) and NIGPAS 100123b (Supplementary Fig. 1 View Fig ), provide views of the external morphology of this species, with an emphasis on its rostral carapace and its associated skeletal attributes. Jianfengia multisegmentalis has a segmented trunk, approximately 2.5 cm in length comprising 27-28 homonomous segments ( Fig. 1a View Fig ). A rostral carapace 5 mm in length and barely 3 mm in width covers the cerebrum and the first three postcerebral segments (Supplementary Table 1). Paired eyestalks extend laterally from the carapace immediately in front of a pair of uniramous postocular ‘ great appendages ’ that originate from beneath the carapace (Supplementary Fig. 1a – c View Fig ). Each ‘ great appendage ’ comprises six podomeres of which the second and third provide an elbow-like articulation 7. The elongated shaft of the third podomere terminates as three articulating blades that together furnish a stubby chela. These appendicular attributes conform to the general category of ‘ great appendages ’ ascribed to members of the paraphyletic clade Megacheira (Supplementary Table. 2), the significance of which is discussed later.
Rostrally, a pair of protrusions extending from the front of the carapace flank a substantial forward-projecting anterior sclerite,which arises from beneath the edge of the carapace with which it likely articulates ( Figs. 1b View Fig , 2a – c View Fig ). Despite considerable flattening typical of Chengjiang fossils, features of the anterior sclerite indicate that it is capped by three areas we interpret as ocellar-like lenses comparable to those described for the anterior sclerites of the deuteropodian Odaraia alata 8, thereby corresponding to frontal eyes of trilobites 9 and the nauplius eye/ocelli of extant pancrustaceans 10, 11. As shown in Fig. 2 View Fig a-c, these putative ocelli overlie a palisade of rod-like components here interpreted as photoreceptors at the base of the anterior sclerite. Superimposition of neural traces from the anterior sclerite of Jianfengia specimen YKLP17299 onto the corresponding exoskeleton of YKLP11117 ( Fig. 2d View Fig ) further supports the presence of ocelli represented by a system of diverging axons from the anterior sclerite.These extend into the most rostral neuropil of the brain in a manner identical to axonal projections from a pancrustacean ’ s ocelli into its rostral cerebrum 10, 11.
Proven by developmental genetics of extant pancrustaceans, the combinatorial activity of Six3, FoxQ2 and hbn gene homologs is required for the development of rostral ocellar photoreceptors whose axons project into the prosocerebrum of the forebrain 12 – 14. The corresponding organization in Jianfengia of axonal projections from the anterior sclerite ( Fig. 2d View Fig ) thus identifies the prosocerebral domain of its cerebrum. Conspicuously absent in extant Myriapoda (and in Fuxianhuiidae ), the nauplius/ocellar visual system therefore appears to be restricted to certain lineages of Artiopoda 8, Trilobita 9, and Pancrustacea 10, 11. Jianfengia further possesses compound eyes that crown each of the paired eyestalks extending laterally from beneath the carapace ( Fig. 1b – e View Fig ). This organization corresponds to eyestalk morphology typifying eumalacostracan crustaceans 15 and other members of Jianfengiidae 16 whose eyestalks evince two articles connected by a suture ( Fig. 1c – f View Fig ). In extant taxa, the combinatorial activity of Six3, Otx and Pax 6 defines the protocerebral domain of the pancrustacean forebrain 12, 17 and its nested optic neuropils, which receive information from the eye ’ s ommatidial array 18. Compound eyes on stalks and the areas to which their associated fossilized optic neuropils project thus indicate the protocerebral domain of the jianfengiid cerebrum.
Reconstructing the brain of Jianfengia
Our initial procedure for reconstructing the cerebrum of Jianfengia ( Fig. 3 View Fig ) followed a routine used previously on the large fuxianhuiid cerebrum where incomplete neural traces from several specimens were mapped as mirror symmetric profiles within an envelope representing the bilaterally symmetric fuxianhuiid head shield 1. For Jianfengia , the neural traces, manifested as blue-black residues or as clusters of grey to near-black granules, were mapped onto a mirror-symmetric envelope for each of four specimens. The initial envelope was defined by the outline of the right frontal carapace and eyestalk of specimen YKLP11117 (from Fig. 1b View Fig ). Flipping a copy of the outline across the animal ’ s midline provided the mirror symmetric envelope, as shown in Fig. 3b View Fig . The envelope was correspondingly adjusted to map neural traces in specimens that showed evidence of taphonomic misalignments, such as lateral displacements of the eyestalks or medial areas (e.g. specimen YKLP1367: Fig. 3c View Fig ). These adjustments facilitate mapping of neural traces irrespective of such distortions, as shown for YKLP11368 ( Fig. 3d View Fig ). Likewise, specimen YKLP11369, in which only half the frontal volume could be retrieved, provided neural traces that mapped into the eyestalk and laterally alongside the esophageal foramen ( Fig. 3e View Fig ). To obtain the final reconstruction, the envelopes and their traces of each specimen were readjusted and registered in the summary envelope as shown in Fig. 3g View Fig . Finally, each tracing in one half of the envelope was mirrored in the other ( Fig. 3h View Fig ). The symmetrical profile from each of the four specimens was then filled and made 33% opaque. All four profiles were superimposed to provide a summed reconstruction of the Jianfengia cerebrum and its connection to the first three contiguous trunk ganglia T1 – T3 ( Fig. 3h View Fig ).
With manual tracing, however, it is impossible to exclude anticipatory bias 19. To meet this challenge, we generated a second reconstruction using a minimum of human intervention. Two specimens were selected,YKLP 11367 and YKLP17299,both of which provide evidence of bilaterally preserved neuropils and tracts. Unlike specimen YKLP17299, whose mirror-symmetric neural traces suggest it is preserved flat ( Fig. 3o View Fig ), the asymmetric disposition of traces in specimen YKLP 11367 ( Fig. 3i View Fig ) indicates a slight taphonomic rotation around the fossil ’ s anteroposterior axis. Assuming that Jianfengia was a member of Bilateria, then these left and right traces in YKLP 11367 each represents a different depth within the specimen and are present on the contralateral side. These neural traces contribute to a mirror-symmetric organization as do the reflected outlines obtained by tracing. Reconstitution required four actions: the elimination of structures beneath a defined gray level (here 87% black of the CMYK scale), thus retaining the darkest puncta; inversion of the image to provide white profiles on a black background followed by the imposition of a Gaussian blur function (here radius expansion R = 10px) that expands and runs together puncta (compare Fig. 3j, k View Fig ). To counteract asymmetry around the midline ( Fig. 3k View Fig ), the right side of the processed image beneath its ipsilateral eyestalk was isolated ( Fig. 3l View Fig ), flipped to the other side and merged with the left half, guided by matching the perimeters of the esophageal foramen ( Fig.3m View Fig ). The left half was then copied, flipped back to become the right half with the two halves joined at the midline ( Fig. 3n View Fig ). This provides a mirror-symmetric depiction of all traces present in the original specimen ( Fig. 3n View Fig ). Finally, tracings pertaining to the ocellar/naupliar system of specimen YKLP17299 ( Fig. 3o View Fig ) were identically processed ( Fig. 3p View Fig ). The mirror-symmetric image of YKLP17299 was superimposed onto that of YKLP11367, aligning their prominent ocellar features to provide the final reconstituted view of the jianfengiid cerebrum ( Fig. 3q View Fig ). This second procedure precludes subjective bias, yet the resultant image corresponds well with that obtained by tracing.
Corresponding branchiopod and malacostracan cerebral organization in Jianfengia
Both reconstruction methods resolved cerebral neuropils rostral to the esophageal foramen and fossilized nerve cords that extend around the esophageal foramen giving rise to neuropils disposed lateral to it. These nerves converge caudally to provide a synganglion immediately posterior to the foramen. The dispositions of these neuropils as well as neuropils defining the lateral expansion of the protocerebrum into the eyestalks correspond to traits typifying the brains described for the crown groups Branchiopoda and Decapoda 5, 18, 20 – 22. As would be expected from observations of extant eucrustaceans, traces of neural tissue within the jianfengiid esophageal foramen ( Fig. 3h, q View Fig ) also align with the standard locations of the appendicular labrum 15. In both reconstructions fossilized axon bundles diverge laterally from the anterior sclerite ’ s ocellar/nauplius eyes to supply the rostral neuropil of the prosocerebrum ( Fig. 2d View Fig ) where they merge with bilateral neuropils anterior and lateral to the esophageal foramen.These protocerebral areas receive the eyestalks ’ nerves which connect a series of three nested neuropils originating from beneath the compound eyes. ( Fig. 3h, q View Fig ).
Next, we determined whether the reconstructed cerebra may correspond to the optic lobes and other neuropils that exist in today ’ s eucrustaceans.Both reconstructions of Fig. 3h, q View Fig allow an interpretive view of the jianfengiid brain ( Fig. 4a – c View Fig ). The lateral extension of the brain into the eyestalks comprises a small first optic neuropil (ON1) beneath the compound retina. This center is contiguous with a voluminous second optic neuropil (ON2) nestled against a smaller third neuropil (ON3). That the three neuropils are homologues of the lamina, medulla and lobula typifying pancrustaceans is supported by their alignment and similarity to the eye stalk neuropils exemplified here by the extant decapod malacostracan Astacus astacus 23 (upper left in Fig. 4a View Fig ). The organization of the circumstomodeal nerve cords and their neuropils, however, align with those of branchiopod crustaceans 21, 24, such as Triops longicaudatus and Artemia salina , whose cerebral nervous systems, other than the optic lobes, are nearly identical to that reconstructed for Jianfengia (lower left, Fig. 4a View Fig ). The jianfengiid brain thus features attributes of both the ground pattern of the malacostracan visual system 18 and the deutocerebral-synganglion circumstomodeal nervous system of adult Branchiopoda, which can also be observed during early development of the decapod brain 21, 22.
Is Jianfengia a member of Tetraconata?
A trait claimed to be exclusive to pancrustaceans,and that inspired the term ‘ Tetraconata ’ as the alternative name for Pancrustacea 25, is the presence of a quartet of Semper cells in each ommatidium of the compound eye. In living pancrustaceans each Semper cell sends four processes from the base of the ommatidium to secrete the transparent protein that builds the ommatidium ’ s light-focusing cone 26, 27. The presence of such an organization in Jianfengia could support its status as a protocrustacean. Specimen YKLP11117 shows a few ommatidia that appear to have lost their cuticular lenses, thus allowing a view beneath them. Combined UV and white light illumination reveal in four ommatidia a geometric arrangement of internal elements that are distinct from possible taphonomic artifacts (Supplementary Fig. 2 View Fig ). Resolving peak intensities in a defined chromatic range (see Methods) reveals grouped iridescent components in four ommatidia. Albeit a small sample,in two ommatidia the groups appear to be organized as a quartet, whereas in the other two ommatidia the resolution is ambiguous in suggesting more than four. Whereas the constrained tetrad arrangement is crucial for the patterning of the pancrustacean compound eye and its ommatidia 26, 27, in the Scutigeriidae — centipedes uniquely possessing compound eyes 28 — the Semper cells contribute at least eight prolongations that could provide the crystalline cone 28, 29. The implications that cone cell ambiguities exclude Jianfengia from Pancrustacea are considered next.
Neurocladistics identifies Jianfengiidae basal to total Mandibulata
Arrangements of putative Semper cells do not provide an unambiguous trait supporting pancrustacean affinity. To clarify the phylogenetic status of Jianfengia we used neural traits for cladistic determination of its relationship with representative mandibulates and chelicerates. This follows the strategy used for a previous neural cladistics study inferring phylogenetic relationships across extant euarthropods 30. Here we assembled a matrix of 120 characters comprising mainly neural traits with additions pertaining to the carapace, cephalic appendages,and tagmatization (Supplementary Table 1). The traits were scored as present/absent across 17 living euarthropod species as well as the Chengjiang fossil Fuxianhuia protensa and Alalcomenaeus 2, 7, the Wuliuan stage Kaili fossil Leanchoilia 5, the BST fossil Mollisonia symmetrica 31 and the fossil limuliid Euproops danae from the Carboniferous Mazon Creek Konservat-Lagerstätte 32. The cladistics analysis was rooted against three non-arthropodan outgroups, the spiralian Paranemertes peregrina , and the cycloneuralians Caenorhabditis elegans and Priapulus caudatus . For parsimony and likelihood analyses we employed PAUP* (Phylogenetic Analysis Using Parsimony*, version 4.0a168) 33 to infer evolutionary relationships. To avoid bias,due to the uncertainty of Semper cell numbers that trait was excluded. For maximum parsimony analyses,all traits were unordered and initially considered under equal weighting ( Fig. 5 View Fig ). We also performed Bayesian analyses on the same matrix in Mr. Bayes (version 3.2.7a), under the Markov k (Mk) model of character evolution 34. The resultant phylogenetic trees and evolutionary relationships were largely congruent across all inference methods, with minor variation in likelihood and parsimony bootstrap support values and Bayesian posterior probabilities (see Supplementary Fig. 4 View Fig ). Notably, Jianfengia multisegmentalis was resolved as basal and sister to Mandibulata in all phylogenetic analyses with various levels of support (Supplementary Fig. 4 View Fig ), whereas the short body megacheirans Alalcomenaeus and Leanchoilia were resolved as basal and sister to total Chelicerata. Fuxianhuia protensa was resolved as a stem mandibulate closely allied with extant Myriapoda.
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