Abstract
The tube-dwelling bristle-worm, Diopatra neapolitana which lives in sand occupying a parchment-like tube is found in common in the tidal flat along the coast of inland seas and frequently is used as a bait. The tube of this worm is characterized by the presence of fragments of shells or sea-weeds and other debris adhering to its upper part, which projects above the surface of the sand. The present study was undertaken to secure information concerning on the life history of this worm, viz., breeding season, development, metamorphosis, growth and age etc. For this purpose observations and measurements were made of worms collected in 1955-1956 from the coast of Maeshiba and Umeyabu, Toyohashi City, Aichi Prefecture. Attempts were also made with success to inseminate the egg of this worm artificially and to culture the larva. The results obtained are summarized as follows: 1) The sexes are seperated and no external morphological difference can be detected between them. In the breeding season, however, they can be distinguished each other by the gonad color externally observable through the body wall. The breeding season lasts from June to early September, with the peak spawning in mid-July and early August. 2) The immature ovarian egg has two strings of nurse-cells which fall off as the egg matures. The matured egg has a diameter of approximately 200 microns. 3) About 13 hours after fertilization at 27.0-29.5°C, the embryo becomes a free-swimming protrochophore larva. After about 3 days the free-swimming larva grows to 0.5mm in body length and sinks to the bottom. About a month after settling, the worm reaches 3-8mm in body length. 4) Judging from the shifts in the modes found on the body-weight frequency distributions of the worms collected from the field, this worm seems to grow as follows: Age 1 yr. 2 yrs. 3 yrs. Total body length (cm) 12.4-13.9 21.1-23.2 28.5-31.7 Total body weight (gr) 1.3-1.7 3.4-4.0 5.7-6.3 5) The relation between the total body weight (W gr) and the total body length (L cm) is given by a formula, W=0.0184L1.6799.
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