The trilobite upper limb branch is a well-developed gill

ESEM and micro-CT observations of Triarthrus eatoni and Olenoides serratus document filament geometry and body-wall attachment consistent with a respiratory upper branch; gas exchange, flow and evolutionary homology remain functional hypotheses rather than direct physiological measurements.

Olenoides serratus is the named Burgess Shale trilobite in the cited appendage comparison; its sample does not establish a direct ancestral relationship.

This profile is limited to the cited Burgess Shale sample in British Columbia and does not establish a genus-wide distribution.

Upper-branch morphology is consistent with a respiratory function, but gas exchange, haemolymph flow, diet and ecological guild are not directly measured.

Olenoides serratus preserves a partly articulated, filament-bearing upper limb branch with body-wall attachment used in the study's structural comparison.

Olenoides serratus is bounded here by the cited Burgess Shale sample from British Columbia, Canada; this named locality sample is not a genus-wide distribution or exact complete range.

Triarthrus eatoni is bounded here by the cited respiratory-appendage sample from Beecher's Trilobite Bed, New York, USA; this named locality sample is not a genus-wide distribution or exact complete range.

The 521–443 Ma trilobite evidence route is a navigation envelope between separate early-trilobite and Beecher's Bed samples, not a lineage duration or continuous occurrence series.