X-diseases in the chaetognathSagitta crassa

Abstract

Two different, hitherto unknown, diseases occurred in two specimens ofSagitta crassa which were individually isolated and maintained in the laboratory. One specimen survived for 24 days, producing a total of 343 eggs and suddenly died without showing any prior symptoms, and upon death had a grotesque appearance. The other had ciliary sense organs the hairs of which became stuck to one another. Ciliary sense organs are important for feeding of chaetognaths; once they become abnormal, the chaetognath may die of starvation. Specimens suffering from X-diseases have not been obtained from field samples so far. Chaetognaths which remained transparent at the time of death included specimens whose ciliary sense organs were attacked by bacteria, those slightly infected by bacteria on their body surface and those with abnormally rough body surfaces. Although the reasons for the development of the abnormality of the ciliary sense organs and body surfaces as well as the mechanism of bacterial infection remain obscure, bacterial infection and abnormalities of the body surface are often observed not only in the laboratory but also in the sea.