Elastoidin fin ray that is slender, sometimes branched distally and present in the embryonic fin fold. Actinotrichia are translucent and exhibit birefringence. [ http://purl.obolibrary.org/obo/uberon/tracker/129 ]
Actinotrichia are required for lepidotrichium development. They are occasionally retained in adult fishes. Further taxon comments from Witten & Huysseune (2007): 'Actinotrichia are found in the embryonic fin fold, along the outer edge of the fin in Actinopterygii, and in the adipose fin in teleosts (Starck 1979; Géraudie and Meunier 1982; Becerra et al. 1983). Only in polypterids has their presence been reported in the joints between adjacent lepidotrichial elements (Géraudie 1988). In the sarcopterygian lineage, actinotrichia are present in coelacanths (Géraudie and Meunier 1980) and in young dipnoans (Arratia et al. 2001).'