To see the unseen: notes on the larval morphology and systematic position of Achanthiptera Rondani (Diptera: Muscidae)

The muscid genus Achanthiptera Rondani (Diptera: Muscidae) was classified within its own subfamily Achanthipterinae for decades
due to a misinterpretation of adult morphology. Conversely, the larval morphology suggested that Achanthiptera should be classified
within Azeliinae, yet no formal changes were implemented based on this source of data. Using scanning electron microscopy (SEM)
and confocal laser scanning microscopy (CLSM), we examined the larval morphology of Ac. rohrelliformis (Robineau-Desvoidy),
Potamia littoralis Robineau-Desvoidy and Australophyra rostrata Robineau-Desvoidy. Despite the challenges posed by the poor
condition of hundred-year-old museum specimens of Ac. rohrelliformis for light microscopy, CLSM examination yielded satisfactory
results. Additionally, CLSM observations revealed peculiar modifications to the cephaloskeleton, including a dome-shaped (second
instar) or spade-like (third instar) anterior rod attached to each mouthhook in Ac. rohrelliformis and P. littoralis. These structural
modifications are likely to enhance the efficiency of food collecting by enlarging the surface of the mouthhooks. The results of our
morphological analyses lead to the conclusion that larvae of Au. rostrata are facultative carnivores, while modified accessory oral
sclerites in Ac. rohrelliformis and P. littoralis suggest a saprophagous feeding strategy. This study contributes new evidence that
Achanthiptera is the sister taxon to Potamia Robineau-Desvoidy, and both are nested within the subfamily Azeliinae.