Breeding and growth ofPsammechinus miliaris(Gmelin)

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Abstract
Gonad growth, test growth, larval settling, and deposition of dark pigment zones in the test of P. miliaris from Raunefjorden, Norway, and from Øresund, Denmark, are described. Seventy-five percent of the one year old urchins from Raunefjorden have immature gonads in their first summer. Maximum numbers of young urchins occur in December–January in Raunefjorden. Growth rates of young urchins from the northern Øresund and from Raunefjorden are identical. Test growth is seasonal with decrease in growth during summer. Individuals kept in aquaria and fed on Laminaria saccharina with epizoic animals show a higher growth rate than those fed on cleaned L. saccharina, and their average test growth equalled that of the fastest growing individuals in the sea. Dark pigment is deposited in the calcareous skeleton from January to May–June.