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Some Aspects of Development in Echinoderes (Kinorhyncha)

Eugene N. Kozloff
Transactions of the American Microscopical Society
Vol. 91, No. 2 (Apr., 1972), pp. 119-130
Published by: Wiley on behalf of American Microscopical Society
DOI: 10.2307/3225404
Stable URL: http://www.jstor.org/stable/3225404
Page Count: 12
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Some Aspects of Development in Echinoderes (Kinorhyncha)
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Abstract

In a species of Echinoderes (close to E. dujardini Claparéde) found intertidally on San Juan Island, Washington, development within the egg envelope leads directly to a juvenile with 11 of the 13 segments characteristic of adult kinorhynchs. There is definitely no distinctive larval stage to which segments are added gradually, as has been claimed. The eggs of Echinoderes are ea. 75 by 65 µ or 80 by 70 µ; the envelope is transparent and about 1 µ thick. The earliest worm-like stage shows no external evidence of segmentation or elaboration of spines. By the time segments can be recognized, the design of the head is well established and scalids have begun to appear. At hatching, the juvenile kinorhynch straightens its body and protrudes its head, thereby tearing open the envelope. It has a trunk length of ca. 115 or 120 µ, and is provided with a long posterior terminal spine, long dorsal spines on segments 10 and 11, long lateral spines on segment 10, and shorter lateral spines on segment 7.

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