Chromosome studies have been performed on some Italian and English Opisthobranchs. The chromosome numbers n = 17, 2n = 34 have been confirmed for the family Philinidae among Cephalaspidea, while n = 13, 2n = 26 have been ascertained in all Nudibranchs, including the species belonging to the families karyologically studied for the first time in the present work. The single elements of the complements are metacentric or only lightly heterobrachial; the mean chiasma frequency and the chiasma distribution ascertained on metaphase I spermatocyte bivalents are seen to be the same when comparing different populations of the same species or closely related species or even species which are divided from each other by considerable taxonomic differences. Chromosome evidence for sistematics and phylogeny may be brought forward by studies on lampbrush chromosomes whose occurrence has been noticed in prophase oocytes I of a number of mollusks.
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Con il contributo del Ministero per i Beni e le Attività Culturali