Online Encyclopedia

SIPUNCULOIDEA

Online Encyclopedia
Originally appearing in Volume V25, Page 151 of the 1911 Encyclopedia Britannica.
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SIPUNCULOIDEA, marine animals of uncertain affinities, formerly associated with the Echiuroidea (q.v.) in the group Gephyrea. Externally, the body of a Sipunculoid presents no projections: its surface is as a rule even, and often glistening, and the colour varies from whitish through yellow to dark brown. The anterior one-quarter or one-third of the body is capable of being retracted into the remainder, as the tip of a glove-finger may be pushed into the rest, and this retractile part is termed the introvert. At the tip of the introvert the mouth opens, and is surrounded in Sipunculus by a funnel-shaped, ciliated lophophore (figs. 1 and 2). In Phascolosoma and Phascolion this funnel-shaped structure has broken up into a more or less definite group of tentacles, which in Dendrostoma are arranged in four groups. In Aspidosiphon and Physcosoma the tentacles are usually arranged in a horse-shoe, which may be double, overhanging the mouth dorsally. On the surface of the funnel-shaped lophophore are numerous ciliated grooves, and each of the tentacles in the tentaculated forms has a similar groove directed towards the mouth. These grooves doubtless serve to direct currents of water, carrying with them small organisms towards the mouth. The skin consists of a layer of cuticle, easily stripped off, secreted by an ectodermal layer one cell thick. Within this is usually a sheath of connective tissue, which surrounds a layer of circular muscles; the latter may be split up into separate bundles, but more usually form a uniform sheet. Within the circular muscles is a layer of longitudinal muscles, very often broken into bundles, the number of which is often of specific importance. Oblique muscles sometimes lie between the circular and longitudinal sheaths. On the inner surface is a layer of peritoneal epithelium, which is frequently ciliated, and at the bases of the retractor muscles is heaped up and modified into the reproductive organs. The ectoderm is in some genera modified to form certain excretory glands, which usually take the form of papillae with an apical opening. These papillae give the surface a roughened aspect; the use of their secretion is unknown. They are best developed in Physcosoma. When the body of a Sipunculoid is opened, it is seen that the body-cavity is spacious and full of a corpusculated fluid, in which the various organs of the body float. The most conspicuous of these is co-educational; founded in 1883), All Saints School (Protestant Episcopal), for girls, and a Lutheran Normal School (1889). The city is the see of a Roman Catholic and of a Protestant Episcopal bishop. The river falls here about zoo ft. in half a mile and provides good water power for manufactures. The total value of the factory products increased from $883,624 in 1900 to 51,897,790 in 1905, or 114.8%. Sioux Falls is a jobbing and wholesaling centre for South Dakota and for the adjacent parts of Iowa and of Minnesota. A quartzite sandstone, commonly known as jasper or " red granite, " is extensively quarried in the vicinity, and cattle raising and farming are important industries of the surrounding country. A settlement was made at Sioux Falls in 1856, but this was abandoned about six years later on account of trouble with the Indians. A permanent settlement was established in 1867, and Sioux Falls was incorporated as a village in 1877 and was chartered as a city in 1883.
End of Article: SIPUNCULOIDEA
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