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n. pl.1.(Zool.) A group of wormlike invertebrates having, along the sides of the body, branchial openings for the branchial sacs, which are formed by diverticula of the alimentary canal. Balanoglossus is the only known genus. See Illustration in Appendix.
Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
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Invertebrate zoologists consider the phyla Dicyemida, Orthonectida, Placozoa, Cycliophora, Entoprocta (Kamptozoa), Chaetognatha, Pterobranchia, and Enteropneusta along with the order Seisonidae.
Nerve cells of Xenoturbella bocki (phylum uncertain) and Harrimania kupfferi (Enteropneusta) are positively im-munoreactive to antibodies raised against echinoderm neuropeptides.
Vargas (1987, 1988) also listed the presence of peanut worms (Sipuncula), Glottidia audebarti (Broderip, 1835) lamp shells (Brachiopoda) and acorn worms (Enteropneusta).
1 Isopoda Natatolana 26.99 [+ or -] 37.45 0.79 gracilis Ancinus 0.63 [+ or -] 1.88 0.02 brasiliensis Mollusca Bilvavia Tivela 3250.01 [+ or -] 2245.09 95.64 mactroides Donax striatus 10.04 [+ or -] 18.48 0.30 Donax 7.53 [+ or -] 18.74 0.22 denticulatus Hemichordata Enteropneusta 15.69 [+ or -] 17.36 0.46 Total 3398.16 [+ or -] 2254.05 Density Table 5.
Growth and metamorphosis of planktonic larvae of Ptychodera flava (Hemichordata: Enteropneusta).
At the bathyal level, the other dominant organisms are in the following order: amphipods, isopods, and tanaidacian crustaceans; in the abyssal plains, tanaidacians, bivalves, and isopods; in the oceanic trenches, bivalves, solenogastres (Aplacophora), acorn worms (Enteropneusta), bryozoans, tanaidacians, and spoon worms (Echiurida).
Acorn worms (Enteropneusta), a solitary class of hemichordates, are marine vermiform invertebrates that generally live concealed in burrows (Hyman, 1959).
At present, 135 hemichordate species are described: 121 are solitary Enteropneusta, or acorn worms; and 24 are colonial, tube-dwelling Ptero-branchia (Appeltans et al., 2012; Halanych and Cannon, unpubl.