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The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, platy, meaning "flat" and ἕλμινς (root: ἑλμινθ-), helminth-, meaning "worm") [4] are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates.
22 paź 2023 · Segmented and unsegmented worms differ in their body symmetry. Segmented worms have bilateral symmetry, meaning their bodies can be divided into two mirrored halves along a central axis. In contrast, unsegmented worms have radial symmetry, with their bodies arranged around a central axis like a pie.
The annelids (/ ˈ æ n ə l ɪ d z /), also known as the segmented worms, comprise a large phylum called Annelida (/ ə ˈ n ɛ l ɪ d ə /; from Latin anellus 'little ring'). [3] [a] It contains over 22,000 extant species, including ragworms, earthworms, and leeches.
The Sipuncula or Sipunculida (common names sipunculid worms or peanut worms) is a class containing about 162 species of unsegmented marine annelid worms. Sipuncula was once considered a phylum, but was demoted to a class of Annelida, based on recent molecular work. [1]
The elongated, unsegmented nematode body is covered by a thick cuticle which is flexible outer covering composed primarily of protein with trace amounts of lipid and carbohydrates. It lines the buccal cavity, esophagus, anus, cloaca, excretory pore and vagina.
Flatworms are unsegmented, bilaterally symmetrical worms that lack a coelom (acoelomate) but that do have three germ layers. Some forms are free living but many are parasitic.
1 lis 2019 · Free-living nematodes, an ancient animal phylum of unsegmented microscopic roundworms, have successfully adapted to nearly every ecosystem on Earth: from marine and freshwater to land, from the polar regions to the tropics, and from the mountains to the ocean depths. They are globally the most abund …
