''Setapedites'' is an extinct genus of

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

offacolid

chelicerates The subphylum Chelicerata (from Neo-Latin, , ) constitutes one of the major subdivisions of the phylum Arthropoda. Chelicerates include the sea spiders, horseshoe crabs, and arachnids (including harvestmen, scorpions, spiders, solifuges, tic ...

from the

Fezouata Formation The Fezouata Formation or Fezouata Shale is a geological formation in Morocco which dates to the Ordovician, Early Ordovician.

of Morocco. The genus contains a single species, ''Setapedites abundantis''.

Description

''Setapedites'' is roughly 6 mm long excluding the telson, with eleven body segments and a prosoma with six appendage pairs. The first appendage pairs are elongated chelicerae, with the other five being biramous appendages. The exopods of these appendages bear

seta In biology, setae (; seta ; ) are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Depending partly on their form and function, protostome setae may be called macrotrichia, chaetae, ...

e on their tips, hence the name ''Setapedites''. The opisthosoma is divided into a pre-abdomen and an abdomen. Each pre-abdomen segment has both a pair of appendages and on the tergites, leaf-shaped tergopleurae, although somite 14 and all of the abdominal somites lack appendages. The first pre-abdominal somite has a large, flap-like exopod. The abdominal somites have fused tergites and sternites forming ring-shaped structures, alongside two pairs of spines derived from the tergopleurae. Under the 11th tergite, a small, symmetrical round structure is preserved, which may be an anal pouch. The telson as the end of the abdomen is roughly as long as the pre-abdomen, with a triangular shape.

Taxonomy

''Setapedites'' shares similarities with ''

Offacolus ''Offacolus'' is an extinct genus of euchelicerate, a group of chelicerate arthropods. Its only species, ''O. kingi'', has been found in deposits from the Silurian period ( Homerian epoch) in the Wenlock Series Lagerstätte of Herefordshire, ...

'' like the elongated chelicerae and limb arrangement, however the number of segments is closer to that of '' Dibasterium''. Unusually, it also shares some features with ''

Habelia ''Habelia'' is a genus of extinct arthropod from the Middle Cambrian, thought to be one of the earliest known relatives of chelicerates. Its fossils have been found in the Burgess Shale in British Columbia, Canada. Fifty-four specimens of ''Habel ...

'' like the anal pouch and structure of the opisthosomal tergites. Phylogenic analysis shows that ''Setapedites'' is closely related to '' Bunaia''.

Etymology

''Setapedites'' translates to "foot with setae" and derives from the characteristic setae of the outer endopod segments. The specific name ''abundantis'' translates to "abundant", referring to how common the genus is within the Fezouata Formation.

References

{{Taxonbar, from=Q131379244 Euchelicerata Fezouata Formation fossils Early Ordovician first appearances Fossils of Morocco Early Ordovician extinctions Ordovician arthropods Fossil taxa described in 2024