Xenacoelomorpha Flashcards
Synapomorphies of Xenacoelomorpha (4)
simple, small, bilateral acoelomates
ciliated epidermis
simple/no digestive track
no excretory, respiratory, and circulatory system
Body for of adults (2)
Small, flat, and worm-like in appearance (usually <5 mm in length).
Soft-bodied and lack segmentation.
Body wall and support
Body Wall: Composed of ciliated epidermis for movement.
Support: No rigid skeletal system; body shape is maintained by a
combination of epidermal cilia and internal muscle layers.
Locomotion and body cavity
Locomotion: Primarily ciliary gliding and some muscular contractions.
Body Cavities: Completely acoelomate—no body cavity or circulatory
system.
Feeding/ digestion and circulation
Nutrition (Feeding/Digestion): Some have a simple sac-like gut, while
others (especially acoels) lack a permanent gut and digest food
intracellularly.
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Circulation: No circulatory system; diffusion is the primary method of
distributing nutrients.
excretion and gas exchange
Excretion (Osmoregulation): Lack specialized excretory organs; likely
rely on diffusion to eliminate metabolic waste.
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Gas Exchange (Respiration): No specialized respiratory structures; gas
exchange occurs via diffusion.
Nervous system
Simple nerve net with a few nerve cords,
lacking a true centralized brain.
Reproduction and development (4)
Some reproduce asexually via fragmentation.
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Others have both sexual and asexual reproduction, often
hermaphroditic.
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Fertilization can be internal or external.
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Direct development is common, with no larval stage.
Habitat (3)
Mostly marine, living in benthic (seafloor) environments.
Often found in interstitial spaces between sand grains.
Some species are symbiotic with other marine organisms.
What were they once classified as?
were once classified within flatworms
(Platyhelminthes) but were later recognized as a distinct group due to
molecular evidence.
What insights do they provide?
early bilaterian evolution due to their
simplicity.
Alternative feeding strategy
absorbing
dissolved organic matter directly from their environment.
