Arenosicaris is an extinct genus of Cambrian from the Blackberry Hill site of Wisconsin, and the oldest phyllocarid known. The genus contains a Monotypic taxon, Arenosicaris inflata.
Description
Arenosicaris is roughly 3 cm long, with only the abdomen and carapace known. No head or thorax limbs have preserved, although there are several structures that may be . The carapace is to subovate, with possible striations on its surface. The rostral plate is unknown, and no median dorsal plate is present. The hinge line is flat or very slightly convex, with the carapace valves being slightly convex as well. The abdomen consists of seven
which decrease slightly in width towards the posterior. Somites 1 to 5 have a pair of
biramous , while somites 6 and 7 lack limbs. The
telson and furcal rami are unknown. These pleopods are divided into three sections like most biramous arthropod limbs. The is short and rectangular, being slightly flattened. The
endopod is incompletely known, while the
exopod is large and U-shaped, decreasing greatly in size near the posterior. No setae are known from the limbs.
Arenosicaris is unusual among phyllocarid fossils for its preservation of limbs, if only partial. The thoracopods were likely quite fragile, hence their poor preservation.
[ Arenosicaris's position is currently uncertain within Archaeostraca, although it may be somewhat related to the suborder Caryocaridina.]
Etymology
Arenosicaris derives from arenosum, meaning "a sandy place" in reference to the unusual preservation in sand, and the Greek καρις, meaning "shrimp", a common crustacean suffix. The species name inflata is in reference to the uncompressed nature of the fossils.[
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