Population and developmental characteristics of the rhizocephalan parasite Sacculina carcini were studied in the Limfjord, Denmark and at Roscoff, France. The frequency of juvenile externae in the Limfjord was higher during summer (69.8% of all externae) than during winter (43%). At Roscoff, 62.6% of externae were juvenile in May-June, but only 8.4% in September. The percentage of juveniles with settled males in the Limfjord was higher in summer (20.7% of all juveniles) compared to winter (6.7%). Juveniles at Roscoff in summer had less success in male acquisition (18.0%). The mean number of settled male cyprids per juvenile externa was 0.56 in summer and 0.12 during winter in the Limfjord, but only 0.27 in the summer at Roscoff. Laboratory kept virgin externae invaded by male cyprids ceased to attract additional males within 5–6 days after the first male settlement and then grew into adults within 3 weeks. Externae without males, kept in isolation, did not grow or show any other signs of maturation. Our results confirm and extend previous data on the role of males and their effect on externa development in S. carcini, and show that the success of male acquisition is susceptible to both seasonal and regional variation.

根状头寄生虫Sacculina carcini的种群和发育特征在丹麦的Limfjord和法国的Roscoff进行了研究。Limfjord中的青少年外生动物的频率在夏季（占所有外生动物的频率）较高，而在冬季（43％）更高。在罗斯科夫（Roscoff），5-6月有62.6％的外生物是幼鱼，而9月只有8.4％。夏季（占所有少年的20.7％），与冬季（6.7％）相比，林福德峡湾有定居男性的少年比例更高。夏季在罗斯科夫（Roscoff）的青少年在男性收购方面的成功率较低（18.0％）。在Limfjord，每个青少年外生的定居男性塞浦路斯人的平均数在夏季为0.56，在冬季为0.12，而在Roscoff，夏季仅为0.27。在第一次雄性定居后的5-6天之内，实验室中被雄性塞浦路斯侵袭的处女原始外部不再吸引其他雄性，然后在3周内长成成年。没有雄性的Externae，保持隔离，没有生长或没有任何其他成熟迹象。我们的研究结果证实并扩展了先前关于雄性的作用及其对雄性外发育的影响的数据。S. carcini，并表明雄性采集的成功易受季节和区域变化的影响。