Rhabditophora

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Rhabditophora is a subphylum of flatworms (phylum Platyhelminthes). It includes all parasitic flatworms (Neodermata) and most free-living flatworms that used to be grouped as Turbellaria. In other words, it contains most species of flatworms, except for the catenulids, which are their sister group.

A defining feature is the presence of lamellated rhabdites—rod-like secretions in the epidermis. In Neodermata these rhabdites are usually absent because the adult epidermis becomes a multi-nucleus (syncytial) layer.

Another key trait is the duo-glandular adhesive system in the skin, made of three cell types: anchor cells, adhesive glands, and releasing glands. This system lets the worm stick to surfaces and then release quickly, often in a second.

Rhabditophorans also have a distinctive protonephridial system. The flame cells and tube cells have overlapping cytoplasmic projections that form a two-cell “weir,” helping with waste removal and osmoregulation.

The group was defined by Ulrich Ehlers in 1985 based on its body plans, and later genetic studies confirmed that Rhabditophora is a single, natural group.