APLACOPHORA. 281 



Order A PL ACOPHOEA v. Ihering. 



Aplacophora IHERING, Jahrb. d. Deutsch. Malak. Ges., 1876, p. 

 136 (as a Class of the Phylum Amphineura, of the Vermes) ; Ver- 

 gleich. Anat. Nervensyst. u. Phylog. Moll., p. 31. 



Telobranchiata KOREN & DANIELSSEN, Arch. Math, og Natur- 

 vid., ii, 1877, p. 123 (as an Order of Opisthobranchiata). See for 

 translation, Ann. Mag. N. H. (5), iii, p. 323. 



"Grade Lipoglossa, Class Solecocmorpha " \_Sco lecomorp ha] LAN- 

 KESTER, Quart. Journ. Mic. Sci. (n. ser.) xvii, p. 448 (1877). 



Solenogastres GEGENBAUR, Grundriss der Vergleich. Anat., (2d 

 edit.), 1878. English trans, by Jeffrey Bell, p. 127 (Division of 

 Vermes). 



Orders Neomenice and Chcetoderma LANKESTER, Encyclop. Brit. 

 (Edit. 9), xvi, art. Mollusca, p. 641 (1883). 



Vermiform Amphineura without calcareous plates along the 

 back ; covered with a spiculose integument, continuous around the 

 body or interrupted by a longitudinal furrow beneath, in which lies 

 the foot, which is much reduced or wanting; gills when present 

 lying in a posterior cavity or cloaca, in which the anus opens. Gut 

 not convoluted, with a blind sack or numerous lateral pouches ap- 

 parently with the function of a liver. Pharynx with or without a 

 radula, or with it represented by one conical tooth. Nervous sys- 

 tem composed of four ganglion-bearing longitudinal trunks, two 

 pedal and two lateral, the latter uniting posteriorly above the gut, 

 and all uniting anteriorly in a circumoesophageal ganglionic ring. 



The Aplacophora or Solenogastres escaped the notice of naturalists 

 until about 1845, when Loven described specimens collected by him 

 under the name Chcetoderma nitidulum. Subsequently M. Sars 

 found but did not describe, another form which he called Solenopus, 

 locating it in the Mollusca. It was not until 1875 that this animal 

 was described and figured as Neomenia carinata by Hubrecht, who 

 at first hesitated whether to place it with the Gephyrian worms or 

 the mollusks. After this time the publications upon Chcetoderma, 

 Neomenia and related forms rapidly multiplied. The discovery of 

 a radula in some of the genera influenced most investigators to con- 

 sider the group molluscan ; and the investigation of the nervous 

 system which proved to show remarkable agreement with Chiton, 

 soon caused the group to be located near the Polyplacophora. In 

 1890, Pruvot, at the Banyuls laboratory, studied the embryology of 

 an Aplacophore, and ascertained that at one stage of development 

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