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Rhabdocoels (Dalyellidae)

Taxonomic group

Rhabdocoels: Dalyellidae

Diagnostic features

The Dalyellids are among the most easily overlooked invertebrates in our fresh waters. They belong to the “rhabdocoels” which are small (typically 1 to 2mm) members of the flatworm Phylum Platyhelminthes. Dalyellids have soft rounded bodies, and when preserved they may resemble small soft seeds rather than animals. A mouth and two eyespots are often visible at one end of the body.

Typical habitats

Dalyellids are most common in wetlands or slow-flowing weedy rivers.


They are likely to feed on small organisms such as protozoa, algae and tiny invertebrates.

Indicator value

  • Hard bottom: unassigned
  • Soft bottom: 0.9

The tolerance values (ranging from 0 to 10) give an indication of which are the sensitive taxa (values of 8 or more) and which are the tolerant taxa (values of 3 or less). For more information see: Indicator species

Most of our records of rhabdocoels are from slow-flowing weedy habitats where water quality is less than pristine. Rhabdocoels have been assigned a soft bottom tolerance value of 0.9, but no hard bottom value has been assigned.