Pelagic Nemerteans1

Abstract

THE power of progressing through the water by swimming has long been known in the nemerteans; thus Nardo mentions it in Cerebratulus marginatus, Grube in Meckelia aurantiaca, De Quafages in Polio, bembix, whilst more recently it has been described in Amphiporus pulcher Q.F.M. A. (Drephanophorus) spectabilitis De Micrura fusca, McI., and Tetrastemng, Abild. But the first truly pelagic nemertean was only brought into notice by Prof. Moseley during the voyage of the Challenger (1875). Now, through the labours of Hubrecht, Verrill, Craven and Heath, Brinkmann, Joubin, Gerarda Stiasny-Wijnhoff, and others, a long list of species from all the great oceans, except perhaps the Antarctic, demonstrates their wide distribution, though they are always thinly scattered, so that, as regards some, only one sex is known. Moreover, whilst the littoral nemerteans as a rule form two marked groups of the Enopla and the Anopla (the armed, with the mouth in front of the ganglia, and the unarmed, with the mouth behind the ganglia), the pelagic forms fall under a section of the armed. They are further distinguished by their comparatively short, flattened, and, in some, translucent bodies, the walls of which are in marked contrast to the firmer tissues of the littoral forms, for the almost gelatinous parenchyma is largely developed. Further, some possess a caudal fin, and a few, in addition, a lateral fin. The dorsal and the ventral longitudinal muscles with vertical bands are best developed. Eyes are often absent and sense organs few and peculiarly modified. The typical proboscis and its sheath, with the armature of the former leaning to that in Drephanophorus, is present, though no mention is made by either Prof. Brinkmann or the present author of the remarkable corpusculated fluid in its sheath. Moreover, the males of the pelagic group carry their spermaries in the cephalic region with or without penes, whilst the females follow the littoral nemerteans in having the ovaries arranged along the body—in this case interdigi-tating with the alimentary cseca. Lastly, some males are provided with a pair of muscular tentacles anteriorly.

References

  1. 1

    "The Pelagic Nemerteans”. By Wesley R. Coe. (Memoirs of the Museum of Comparative Zoology at Harvard College, Cambridge, U.S.A.) Vol. 49, pp. 242+30 Plates. 1926.

  2. 2

    Vide NATURE, July 4, 1918, p. 353.

  3. 3

    Trans. R. Soc. Edin., vol. 25, pp. 305-433.

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M., W. Pelagic Nemerteans1. Nature 120, 315 (1927). https://doi.org/10.1038/120315a0

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