endarrerides

Endarrerides is a taxonomic term used in paleontology to refer to a proposed clade of extinct marine arthropod‑like organisms known primarily from fossil exoskeletal remains. The name derives from a distinctive posterior feature common to the group, a tail structure that appears to extend the body rearward. The composition of Endarrerides varies among authors, but typically includes several genera from late Paleozoic marine deposits.

Taxonomic placement is contested. In many accounts Endarrerides is considered part of the arthropod stem group, with debated affinities to crustaceans, chelicerates, or a separate lineage of problematic fossil taxa. Diagnostic features cited include a firmly calcified dorsal shield of anterior segments, a series of lateral plates along the thorax, and a unique posterior telson or tail fan. Limbs are generally described as short, with some specimens showing paired appendages that suggest a benthic, bottom-dwelling lifestyle.

Fossil occurrences are reported mainly from shallow marine formations in what is now Europe and North America, dating to the late Paleozoic era. The ecology proposed for Endarrerides suggests a benthic detritivore or scavenger, living in low-energy environments and contributing to the seabed's recycling of organic matter.

Because the group is defined largely by posterior morphology and fragmentary material, its validity is debated, and some researchers consider Endarrerides to be a paraphyletic assembly rather than a natural clade. Ongoing discoveries and more complete specimens may either consolidate it as a distinct lineage or dissolve it into better-supported taxa.