Rev. 10/30/2019
Kingdom Animalia, sub-kingdom Metazoa - Acoelomata
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Phylum Coelenterata e.g., Hydra.
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Phylum Platyhelminthes Include:
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![]() Anterior portion of flatworm - probably Bipalium sp. |
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![]() Flatworm - Bipalium sp.? Photograph by Joan Maurer, Milwaukee County Zoo, Milwaukee, WI |
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![]() Bipalium sp. - Yolo County, California |
Turbellaria are "free-living" flatworms. They are generally predators of soil invertebrates, including earthworms. Some species can become pests in commercial earthworm beds. The worms are not able to conserve water so they are usually in humid habitats like earthworm burrows. They only emerge when the soil is saturated and their refuges waterlogged; then they are often seen in water puddles.
A Turbellarian that is frequently seen in northern California is Bipalium sp. (maybe B. kewense but there are other species). Bipalium kewense can be up to a foot long and the head is slightly expanded; the basic color is dark orange, but it tends to look darker due to black longitudinal stripes. The ventral surface is less dark. It has numerous eyes scattered over the anterior end. Thought to reproduce by fragmentation (asexually), as well as sexually.
Phylum Nemertea Classes:
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Phylum Nematoda Classes:
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Phylum Nematomorpha Nematomorpha (from the Greek nema, "thread," and morphe, "shape"); horsehair or gordian worms, e.g. Gordius
Female anterior (top), female posterior (lower left) and male posterior (lower right) of Paragordius. |
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The first known fossil record of Nematomorpha dates from
the Eocene (40 - 70 million years ago), but some suggest the group may have
evolved in the Paleozoic Era (over 500 million years ago).
Nematomorpha larvae are parasites aquatic and terrestrial invertebrates, including notably grasshoppers, crickets, locusts, katydids, beetles, caddisflies, dragonflies, spiders, millipedes, centipedes, crustaceans, and leeches. Horsehair worms are usually seen in the adult, free-living stage near edges of ponds and streams. Nematomorphs can be 1 m long and 1-3 mm diam. Color ranges between light tan to dark brown. Males are smaller than females. Locomotion of adult horsehair worms is a slow whipping action; males are more active than females. Horsehair worms reproduce sexually, in spring, early summer, or autumn. Eggs, often numbering in the millions, are laid in long gelatinous strings. For aquatic forms, the incubation period may range between 15 and 80 days, depending upon water temperature. After hatching, larvae are thought to encyst on vegetation along the water's edge soon after hatching where they are ingested by their hosts. The larva then burrows its way through the intestinal wall into the host's body cavity, continuing its development. When ingested by inappropriate hosts, the cyst may degenerate and then reencyst in the tissues of the host. If this inappropriate host is then ingested by one of its predators, the cyst may again disintegrate and continue its life cycle in the new host. After entering the body cavity of an appropriate host, the larva grows and develops into a tightly coiled mass in the host. One to several horsehair worms may occur in a single host. It has been suggested that hosts seek water when the horsehair worm is ready to emerge. Once the host enters the water, the horsehair worm breaks through the body wall of the host. Newly released horsehair worms soon die if they do not have access to water. The common name, gordian worm, is traced back to the gordian knot tied by Gordius, king of Phrygia around 330 B.C. According to mythology, Gordius tied his chariot to a pole and declared that whoever could undo the knot would be ruler of all Asia. Horsehair worm is probably derived from the appearance of the worms in water. Over 230 species of nematomorphs have been described; between 4 and 16 genera occur in North America. Identification of species is based on microscopic surface patterns and sculpturing of the cuticle. Source: Wetzel and Watermolen
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Phylum Acanthocephala
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Phylum Rotifera
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Class Bdelloidea. female of Philodena roseola |
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Phylum Kinorhynchia
Class Homalorhagea; Pycnopyes frequens. Adult on left, anterior retracted; anterior extended on right. |
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Phylum Priapulida
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Phylum Endoprocta
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All the above phyla contain unsegemented organisms. In earlier classifications (e.g. ref Hyman, 1930s) all were considered classes of a single phylum, the Aschelminthes.
Note: Annelida, Arthropoda etc. are coelomate, and segmented.
Maggenti, A.R. 1981. General Nematology.
Borradaile, L.A., L.E.S. Eastham, F.A. Potts and J.T. Saunders. 1961. The Invertebrata. Cambridge University Press.
Dindal, D.L.(ed). 1990. Soil Biology Guide. John Wiley, NY.
Mark J. Wetzel, INHS Center for Biodiversity, and Dreux J. Watermolen, Wisconsin Department of Natural Resources, Madison.
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