Qinscolex spinosus () is an extinct monotypic genus of armored stem-group scalidophoran from the early-Cambrian aged Kuanchuanpu Formation of South China.
Etymology Qinscolex derives its genus name from "Qin" the ancient name of the Shaanxi province where it was found, and σκώληξ is the Greek word for "worm", the species name spinosus is Latin for spinose which refers to elements found on the trunk of Qinscolex.
Description Qinscolex is a worm-like animal known from the fragmentary remains of a juvenile or subadult specimen that measures 1.8mm long and 1.13mm wide. The cuticle of Qinscolex was flexible, resulting in deformed fragments after fossilization.
Proboscis The proboscis is composed of an introvert with the capability to fully invert itself into the trunk, 100 hollow spine-shaped scalids are present on the introvert and are densely packed in irregular arrangements.
Scalids vary in size from the shortest 100μm long and 40μm wide at the scalid's base to 400μm long at the introvert's anterior. Since the holotype was found with its proboscis inverted it is unknown if a pharynx and a set of pharyngeal teeth were present on the anterior are of the proboscis.
Trunk
There is a clearly defined boundary between the trunk and proboscis due to the expanded base of the spinose sclerites providing enough differentiation from scalids on the proboscis. Sclerites are confined to 10 annuli with 40-50 spinose sclerites being present on a given annulus as well as an unusually large sclerite between the sixth and seventh annulus that measures 340μm long and 300μm wide.
The size of a given sclerite and the annulus it resides on vary, following a trend of increasing in length from the first to tenth annulus with the sclerites getting wider as well as longer. The smallest sclerites are measured at 35μm long and 29μm wide, while sclerites found on the 8th and 9th annuli are 150μm long and 60μm wide. The ninth annulus measures approximately 160 μm in length while the first annulus is 34μm long, annuli after the tenth are unknown due to the posterior trunk not being known.
Classification Qinscolex is an enigmatic taxon due to the holotype's fragmentary nature, resulting in a tentative assignment to total-group Scalidophora due to the presence of sclerites indicating that Qinscolex is more derived from the cylconeuralian common ancestor than nematoids. The derived position of Qinscolex creates an evolutionary grade within Scalidophora without living descendants, requiring it to be placed on the group's stem.
Distribution Qinscolex is only known from the holotype which was recovered from Fortunian rocks found in the Kuanchuanpu Formation.
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