Data from: A new species of the Cambrian bivalved euarthropod Pectocaris with axially differentiated enditic armatures

Although first described in 1999, the early Cambrian Pectocaris remains a
poorly known euarthropod genus. As of now, two species, Pectocaris
eurypetala and Pectocaris spatiosa, are known from the Chengjiang biota.
Here, we report a third species, Pectocaris inopinata sp. nov., which
bears a pair of stalked eyes attached to an anterior sclerite, a pair of
short but stout antennae, 29–35 cephalothoracic segments each
corresponding to a pair of biramous appendages, 11–12 limbless segments
carrying two rows of ventral spines and one row of dorsal spines, and a
pair of broad telson flukes decorated with short marginal spines. Most
strikingly, the endopods of anterior trunk appendages are each axially
differentiated with two rows of setulose endites proximally and claw-like
paired spines distally, in contrast to the endopods of posterior trunk
appendages that carry two rows of setulose endites but lack claw-like
paired spines. Phylogenetic analysis shows that P. inopinata, the other
two Pectocaris species, together with their close relative Jugatacaris
agilis belong to the same monophyletic clade. Our study reveals
considerable difference in appendicular details and therefore presumably
niche differentiation among Pectocaris and Jugatacaris species, as well as
some other bivalved euarthropods in the Cambrian with similar overall
appearances.