Palaeonemertea
Palaeonemertea is a class of ribbon worms within the phylum Nemertea. They are commonly known as “primitive nemerteans” or “paleonemerteans.” These worms are generally small, often with a flattened body, and are characterized by their lack of a proboscis, a key feature of most other nemerteans.
Characteristics
Palaeonemerteans possess several distinctive characteristics:
- Lack of a proboscis: Unlike most nemerteans, they do not have a proboscis, a muscular, eversible tube used for capturing prey.
- Simple morphology: They have a simpler body structure compared to other nemerteans, with a less complex nervous system and fewer sensory organs.
- Direct development: Unlike many nemerteans with a larval stage, palaeonemerteans develop directly from the egg, skipping the larval phase.
- Mostly marine: Palaeonemerteans are primarily found in marine environments, with some species living in freshwater or terrestrial habitats.
Environments
Palaeonemerteans are typically found in various marine habitats, including:
- Intertidal zones: They can be found in the area between high and low tide marks.
- Subtidal zones: They inhabit areas below the low tide mark, where they are often associated with benthic communities (organisms living on the seabed).
- Deep sea: Some species of palaeonemerteans have been discovered in deep-sea environments.
References
Palaeonemertea (sciencedirect.com)
Phylogeny and Classification of Palaeonemertea (ncbi.nlm.nih.gov)