Abstract
The embryonic mitosis of Clavelina lepadiformis is characterized by the presence of precociously separating daughter kinetochores and by an extreme shortening of chromosomes during prophase and prometaphase. The chromosomes of Clavelina lepadiformis are all metacentric; differentiated sex chromosomes are not present. The same haploid number of chromosomes, n=9, has been found in both populations of the Lagoon of Venice and of the west coasts of Scotland. Both oocyte and spermatocyte bivalents possess chiasmata.