Kinorhyncha

Kinorhyncha, an isolated group of minute animals containing the single genus Echinoderes F. Dujardin, with some eighteen species. They occur in mud and on sea-weeds at the bottom of shallow seas below low-water mark and devour organic débris.  
  
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(After Hartog, from Cambridge Natural History, vol. ii., “Worms, &c.,” by permission of Messrs. Macmillan & Co., Ltd.)  
  
b, bristle; cs, caudal spine; ph, pharynx; s & s′, the spines on the two segments of the proboscis; sg, salivary glands; st, stomach.  
  
The body is enclosed in a stout cuticle, prolonged in places into spines and bristles. These are especially conspicuous in two rings round the proboscis and in the two posterior caudal spines. The body is divided into eleven segments and the protrusible proboscis apparently into two, and the cuticle of the central segment is thickened to form three plates, one dorsal and two ventrolateral. The cuticle is secreted by an epidermis in which no cell boundaries are to be seen; it sends out processes into the bristles. The mouth opens at the tip of the retractile proboscis; it leads into a short thin-walled tube which opens into an oval muscular gizzard lined with a thick cuticle; at the posterior end of this are some minute glands and then follows a large stomach slightly sacculated in each segment, this tapers through the rectum to the terminal anus. A pair of pear-shaped, ciliated glands inside lie in the eighth segment and open on the ninth. They are regarded as kidneys. The nervous system consists of a ganglion or brain, which lies dorsally about the level of the junction of the pharynx and the stomach, a nerve ring and a segmented neutral cord. The only sense organs described are eyes, which occur in some species, and may number one to four pairs.

The Kinorhyncha are dioecious. The testes reach forward to the fifth and even to the second segment, and open one each side of the anus. The ovaries open in a similar position but never reach farther forward than the fourth segment. The external openings in the male are armed with a pair of hollowed spines. The animals are probably oviparous.

Literature.—F. Dujardin, Ann. Sci. Nat., 3rd series, Zool. xv. 1851, p. 158; W. Reinhard, Zeitschr. wiss. Zool. xlv. 1887, pp. 401-467, t. xx.-xxii.; C. Zelinka, Verh. d. Deutsch. Zool. Ges., 1894.

(A. E. S.)