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A chaeta or cheta (from Ancient Greek χαίτη (khaítē) 'crest, mane, flowing hair'; pl. chaetae) is a chitinous bristle or seta found on annelid worms, although the term is also frequently used to describe similar structures in other invertebrates such as arthropods.
In most species the edge of the mantle also bears movable bristles, often called chaetae or setae, that may help defend the animals and may act as sensors. In some brachiopods groups of chaetae help to channel the flow of water into and out of the mantle cavity.
Depending partly on their form and function, setae may be called hairs, macrotrichia, chaetae, or scales. The setal membrane is not cuticularized and movement is possible. Some insects, such as Eriogaster lanestris larvae, use setae as a defense mechanism, as they can cause dermatitis when they come into contact with skin. [5]
There are four bundles of one to twenty-five chaetae on each segment; these have muscles attached to their bases and can be extended or retracted. [2] Leeches, order Hirudinida, [4] mostly have flattened bodies, usually tapered at both ends. They have a fixed number of segments, 33, but the segmentation is not visible externally because the ...
The worm has 21 segments and 16 of them bear chaetae (the bristled setae of polychaetes). The face is somewhat flattened. The body is cylindrical, but tapers slightly toward the posterior end. In life, the worm is transparent, with ring-shaped integument (scaly ridges) along the back, and discontinuous brown stripe markings.
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Polychaeta (/ ˌ p ɒ l ɪ ˈ k iː t ə /) is a paraphyletic [1] class of generally marine annelid worms, commonly called bristle worms or polychaetes (/ ˈ p ɒ l ɪ ˌ k iː t s /).Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are made of chitin.