Antennacanthopodia
A Cambrian lobopodian and stem-onychophoran with two antenna pairs.
Antennacanthopodia is a small lobopodian from the Chengjiang biota, dating to about 520 million years ago. It is the only widely accepted stem-onychophoran lobopodian from the Cambrian period, showing traits such as two pairs of antennae and stubby legs with foot pads. The animal is similar to modern velvet worms and helps clarify the early evolution of the onychophoran lineage.
Quick Facts
- Species
- gracilis
Facts from the source article.
Discovery and naming
The two known Antennacanthopodia fossils come from the upper Yu'anshan Member of the Lower Cambrian Heilinpu Formation, near the Maotianshan Shales in Yunnan, China, which links them to the Chengjiang Biota. The holotype (ELEL-EJ081876) was dug up at the Erjie section in the Eoredlichia-Wutingaspis Biozone, while the paratype (ELI-JS022643) was found at the Jianshan section. Both are roughly 520 million years old, from Cambrian Series 2 Stage 3. The genus name, from Latin "antennatus" and "acanthopodus," points to its many antennae and spiny lobopods; the species name "gracilis" is Greek for slender or graceful.
Description
Both fossils are dorsoventrally compacted in mudstone, with the holotype better preserved. Excluding appendages, the holotype is 1.4 cm long. Soft tissues appear as a purplish black film, while sclerotized cuticle details are reddish-brown. The animal has two pairs of antennae: the first pair is double the head length and one-quarter the body length, with faint ridges at the base; the second pair is shorter and likely a modified appendage. Which segment the second antennae belong to is unclear, as the animal apparently lacked jaws. The original description hypothesized they were homologous with slime papillae (third head segment), but later studies, noting the absence of jaws, placed them on the second head segment. At the base of the first antennae are rounded black specks interpreted as ocelli, similar to those in modern velvet worms in proportion, placement, and head segment origin. The mouth position is unclear; ancestral character reconstruction suggests a ventral-facing mouth, but this is not preserved. The trunk has nine segments, each with a pair of legs, and tapers to an end projection with two cirriform structures. The body surface bears rows of tiny spines, four per segment, found on dorsal and lateral sides from the second to fourth trunk segments, likely continuing along the entire trunk. Unlike many lobopodians, Antennacanthopodia lacks sclerotized plates or tube-like attachments on its back.
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