ŒCup cell disease¹ in the colonial tunicateBotryllus schlosseri

[摘要] ABSTRACT: A new progressive, fatal disease called Œcup cell disease¹ was characterized in ex situ cultures of Botryllus schlosseri, a colonial tunicate. The disease originated as a few dark spots growing within zooids. The infected coloniesthen started to deteriorate, morphologically diagnosed by ampullar retraction, lethargic blood circulation and by a swollen and soft tunic matrix. In later stages of the disease, developed buds were also affected. Many large black dots were scatteredwithin the tunic matrix, and zooids were transformed to opaque, dilated, sac-like structures, signaling impending death. Colonies were infected periodically, even without direct tissue contact. The time course from first appearance to colony death rangedbetween 30 and 45 d. Histological studies, in vitro culturing of blood cells and blood smears revealed the existence of numerous cup-like cells (up to 4.8 µm diameter on average) with a yellowish cell wall and transparent cytoplasm that was notstained by various dyes (except azocarmine-G). Cells were refractive under bright-field illumination and revealed a flattened wall with flanges, characteristic of species of the phylum Haplosporidia. Cup cells aggregated in blood vessels and in internalparts of zooids and buds and were phagocytosed by blood cells. In a single case, plasmodia-like structures were found only in the tunic matrix of an infected colony. This is the first record in botryllid ascidians of an infectious lethal diseaseassociated with haplosporidian protists.

[学科分类] 生物科学（综合）

[关键词] Ascidians;Botryllus;Disease;Haplosporidia;Mariculture