Dalyelliidae


Dalyelliidae is a family of flatworms belonging to the order Rhabdocoela. The family Dalyelliidae represents the most diverse group within the Dalyellioida. Although a number of species also inhabit marine and brackish waters, the majority are free-living in freshwater environments. Notably, the only known taxon to exhibit symbiotic habits in a broad sense is the ''Varsoviella.''

Genera

As of 2007, Dalyelliidae included 16 genera, ten of which are confined to freshwater habitats:Austrodalyellia Hochberg & Cannon, 2002 Castrella Fuhrmann, 1900 Dalyellia Gieysztor, 1938 Fulinskiella Gieysztor & Szynal, 1939Gieysztoria Ruebush & Hayes, 1939 Haplodidymos Hochberg & Cannon, 2002Microdalyellia Gieysztor, 1938 Sergia Nasonov, 1923Varsoviella, Gieysztor & Wisniewski, 1947Vaillantiella Luther, 1955
Other Genera include:Alexlutheria Karling, 1956Axiola Luther, 1955
Among these, the genera with the highest numbers of species and the widest distribution are Gieysztoria, Microdalyellia, and Dalyellia, the remaining genera are more limited.''''

Distribution

The neotropical region

Within the Neotropical region, Gieysztoria is the most specious genus, with 24 described species.' These taxa exhibit differences in male stylet morphology compared to their European counterparts, with Neotropical species showing greater structural complexity.' Other genera in this region are poorly represented: Dalyellia, Microdalyellia, and Sergia.''''

Argentina

In Argentina, seven species of Gieysztoria have been recorded: G. santafeensis, G. quadrata, G. coronae, G. tigrensis, G. pseudodiadema, G. variata, and G. falx.'''' Additionally, a single species of Microdalyellia and one species of Dalyellia are known.''''