Xenacoelomorpha
Xenacoelomorpha is a phylum of small, bilaterally symmetric, free-living worms that are found in marine environments. They are typically less than 5 mm in length and have a simple, unsegmented body plan. Xenacoelomorpha are characterized by the absence of a digestive tract, a lack of specialized sensory organs, and the presence of a single opening that serves as both mouth and anus. They are known for their remarkable regeneration abilities, being able to regrow lost body parts.
Common Names
Xenacoelomorpha are commonly referred to as "xenoturbellids" or "acoel flatworms," although the latter term is somewhat misleading as they are not true flatworms (Platyhelminthes). The name "Xenacoelomorpha" itself comes from the Greek words "xenos" (strange), "koilos" (hollow), and "morph" (form), referring to their unique body structure.
Characteristics
Xenacoelomorpha possess several distinct characteristics that set them apart from other worm groups:
- Absence of a digestive tract: They lack a traditional digestive system and absorb nutrients directly through their skin.
- Simple body plan: Their body is unsegmented and lacks specialized organs, with only a few cell types.
- Single opening: They have a single opening that serves as both mouth and anus, called a "mouth-anus" or "cloaca".
- Lack of specialized sensory organs: They have limited sensory capabilities and rely on simple sensory cells scattered throughout their body.
- Remarkable regeneration: Xenacoelomorpha are known for their ability to regenerate lost body parts.
Environments
Xenacoelomorpha are predominantly found in marine environments, particularly in intertidal zones, shallow coastal waters, and deeper seafloors. They typically inhabit soft sediments, algae, and other marine substrates.
References
For more information on Xenacoelomorpha, you can refer to the following resources: