Angelacanthus acus (synonym Diplacanthus acus) is a species of Devonian acanthodian from the Waterloo Farm lagerstätte in South Africa. It is the only species in the genus Angelacanthus.
Description Angelacanthus was described from a near complete whole-bodied impression discovered in 1999 during roadworks cutting the Waterloo Farm lagerstätte.Gess, Robert W. and Whitfield Alan K. (2020). "Estuarine fish and tetrapod evolution: Insights from a Late Devonian (Famennian) Gondwanan estuarine lake and a southern African Holocene equivalent". Biological Reviews. doi:10.1111/brv.12590. The type specimen of Angelacanthus is approximately 100 mm long and has exceptionally long and thin ribbed spines. The intermediate spines are, conversely, extremely reduced. Unusually it preserves complete outlines of many of the fins.
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