A Cambrian soft-bodied conical animal illustrates the origins of lophophorate phyla

Abstract

The origin and early evolution of lophotrochozoans remain a difficult but crucial issue in reconstructing metazoan phylogeny. Exceptionally preserved fossils have provided hopeful information for resolving this lophotrochozoan problem. Here we identify that Conicula striata, a soft-bodied conical animal from the early Cambrian Chengjiang Lagerstätte, has mosaic characteristics of different lophophorate phyla. C. striata possesses a phoronid-like vermiform trunk housing a U-shaped gut and a coiled lophophore comprising ≥12 arms with numerous tentacles, but it also bears brachiopod-like features including an undivided mantle enclosing lophophore and a pedicle-like protrusion on annulated trunk. Phylogenetic analysis retrieves C. striata as a total-group lophophorate and as an intermediate taxon between Phoronida and Brachiopoda. This suggests that the bivalved architecture of brachiopods originated from an undivided mantle in a phoronid-like ancestor, and that the ancestral vermiform trunk became reduced during the origin of Brachiopoda, illuminating the origins of body plans in the lophophorate phyla.

An early Cambrian polyp reveals a potential anemone‐like ancestor for medusozoan cnidarians

“…100–150 μm wide; Zeng et al . 2022) is larger than the expected diameter of tentacles borne on paired arms of lophophorates (only 10–60 μm in size; see measured data in Fig. 7, Table S2).…”

“…The presence of such branches on arms is a feature already known, but not described in Zeng et al . (2022), to define the tentacle pattern of octocoral cnidarians, suggesting that if these features are substantiated by further specimens they might support a cnidarian affinity over a lophophorate affinity in any case.…”

“…1999) and this hypothesis was reformulated recently in a preprint, in which C. striata was interpreted as an intermediate taxon between brachiopods and phoronids (Zeng et al . 2022). These authors rejected the cnidarian hypothesis (Zhao et al .…”

“…Zeng et al . (2022) further interpreted a tubular extension as emerging from this patch laterally, as intestine with an anus opening near the conical skeleton wall (Zeng et al . 2022, fig.…”

“…There is no clear evidence to show that the presence of branches along the interpreted arm fringe, even when the ‘arms’ are stretched out of the body, as seen either in Zeng et al . (2022, fig. 2a, b) or this study (Fig.…”