#1
Dear Colleagues This excellent larvae, as I think - Sciomyzidae-I've found in the freshwater sponge (Spongilla lacustris), in the river Seversky Donets, Ukraine. These larvae gnaw tunnels in the sponge, although thesnails were many, but I did not notice that they were attacked by larvae. I would welcome any assumptions of what the larvae.
Sincerely Victor.
#3
Dear Chironomus_1990
although the larva resembles a Sciomyzidae, the behaviour is not.
I can think of only one other family with (semi-)aquatic immature stages looking like your larva i.e. Scatophagidae. As your larva looks like a very immature stage (first/second) the behaviour/fouraging method of these larva can be somewhat different of that of later instars. The larva of Scatophagidae with aquatic stages are either (leaf)miners of predatory. You must know that many other insectlarva (for instance Chironomidae- and caddisfly-larva) fourage within freshwatersponges, so you larva may infact not feed on the sponge itself but is hunting for these larva.
According to Smith (1989) Cosmetopus, Microprosopa, Pogonota, Chaetosa, Trichopalpus, Spaziphora, Coniosternum, Acanthocnema and Hydromyza are such genera. If you are able to add a photo of the prothoracic spiracle (a pair of lobed extensions of the trachea on both sides of the second thoracic segment) maybe an identifcation to family level is possible. In the known species of aquatic Scatophagidae this spiracle is multi-branched.