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, 10 of which are confined to freshwater habitats: Austrodalyellia Hochberg & Cannon, 2002 Castrella Fuhrmann, 1900 Dalyellia Gieysztor, 1938 Fulinskiella Gieysztor & Szynal, 1939 Gieysztoria Ruebush & Hayes, 1939 Haplodidymos Hochberg & Cannon, 2002 Microdalyellia Gieysztor, 1938 Sergia Nasonov, 1923 Varsoviella, Gieysztor & Wisniewski, 1947 Vaillantiella Luther, 1955 Other Genera include:
Alexlutheria Karling, 1956 Axiola Luther, 1955 Among these, the genera with the highest numbers of species and the widest distribution are Gieysztoria (approximately 75 species), Microdalyellia (42 species), and Dalyellia (11 species), 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 (one species), Microdalyellia (three species), and Sergia (one species).
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 (M. fairchildi) and one species of Dalyellia (D. obscura) are known.
References