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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.
The first body segment with 1-2 pairs tentacular cirri without aciculae. Compound setae are present. Notopodia are distinct (rarely reduced), usually with more flattened lobes, notosetae compound falcigers and/or spinigers (rarely notosetae absent).
Nereis is a genus of polychaete worms in the family Nereididae. It comprises many species, most of which are marine. Nereis possess setae and parapodia for locomotion and gas exchange. [1] They may have two types of setae, which are found on the parapodia. Acicular setae provide support.
The micrometer-scale setae branch into nanometer-scale projections called spatulae. [6] A Tokay gecko's two front feet can sustain 20.1 N of force parallel to the surface using approximately 14,400 setae per mm 2. This equates to ~ 6.2 pN per seta, but does not sufficiently account for the overall stickiness behavior shown by the foot pads. [7]
The worm then creeps out backward from the coat and deposits either fertilized zygotes or both ovae and sperm into the coat, which is then packed into a cocoon. The zygotes then develop directly in the cocoon without passing through a larval stage (as opposed to other annelids, e.g. Polychaeta.)
Arenicolidae is a family of marine polychaete worms. They are commonly known as lugworms and the little coils of sand they produce are commonly seen on the beach. Arenicolids are found worldwide, mostly living in burrows in sandy substrates.
Next the anterior circular muscles relax, and a wave of circular contraction moves backwards along the worm. [6] At the same time, the cheatae expand to grip the ground as the body shortens and are retracted as it lengthens. The steps are typically 2 to 3 cm (0.8 to 1.2 in) long and the worm moves at the rate of seven to ten steps per minute.
Lumbricus terrestris is a large, reddish worm species thought to be native to Western Europe, now widely distributed around the world (along with several other lumbricids). In some areas where it is an introduced species, some people consider it to be a significant pest for out-competing native worms. [1]