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(worms), a heterogeneous group of invertebrates that includes about 46,000 species. As a general rule, worms have an elongated body whose walls consist of a cutaneous covering and musculature (the musculocutaneous sac). Locomotion is mainly peristaltic. Together with mollusks and arthropods, the Vermes belong to the group Protostomia. They cover an extensive morphophysiological range in the evolutionary series of invertebrates.
In the 19th century, the Vermes were regarded as a separate phylum. Scientists now consider that they constitute several independent phyla: Plathelminthes (flatworms), Nemathelminthes (nematodes), Nemertini, Echiurida, Sipunculida, and Annelida. The first three phyla are often united under the designation Scolecida. The remaining phyla are usually united with mollusks and arthropods in the higher group of trochophores (Trochozoa). Some zoologists consider Annelida and Arthropoda as subphyla of an extensive phylum known as Articulata.
REFERENCESRukovodstvo po zoologii, vols. 1–2. Moscow-Leningrad, 1937–40.
Beklemishev, V. N. Osnovy sravnitel’noi anatomii bespozvonochnykh, 3rd ed., vols. 1–2. Moscow, 1964.
A. V. IVANOV