hemitrichium

(plural hemitrichia))

one of the pair of slender rod-like structures that compose a lepidotrich or soft fin ray. The hemitrichia are segmented and often branched. The segments are movably held together by flexible collagenous fibres and joined at their distal tips by fused actinotrichia. Proximally the hemitrichia are expanded to provide for the attachment of muscles (erectors, depressors, and inclinators) and for articulation with the fin ray supports