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Physiology of the ciliate Orchitophrya stellarum and its experimental infection of Leptasterias spp.

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Orchitophrya stellarum Cépède, 1907 is a facultative ciliate that parasitizes male asteriid sea stars in the North Atlantic and Pacific oceans. The ciliate also exists in seawater where it feeds on bacteria associated with tissue or yeast. This study is designed to determine the tolerance, growth rate, contractile vacuole activity, and infectivity to Leptasterias Verrill, 1866 spp. as a function of the sea star’s reproductive cycle stage. The tolerance range of O. stellarum in seawater containing bacteria is 2 practical salinity units (PSU) at 8°C and 12.5 PSU at 25°C; the ciliate tolerated a temperature range of 3–27°C at 30 PSU. Ciliate population growth is most rapid at 24°C and is minimal at 3 and 27°C at 30 PSU. The ciliate’s contractile vacuole cycle frequency increases at low salinity, indicating increased water volume regulation as a function of decreased salinity. Unparasitized male Leptasterias spp. can be infected experimentally by injection of a culture of O. stellarum into the rays or from a culture in ambient seawater only when the testes are at full size, but the ciliates do not invade ovarian tissue. The normal path of entry of O. stellarum into the testes of reproductively mature male sea stars probably takes place through gonopores.

Orchitophrya stellarum Cépède, 1907 est un cilié parasite facultatif des étoiles de mer (Astériidae) mâles dans le nord de l’Atlantique et du Pacifique. Le cilié vit aussi en eau de mer où il se nourrit des bactéries associées aux tissus et aux levures. Notre étude a pour objectif de déterminer sa tolérance, son taux de croissance, l’activité de sa vacuole contractile et son infectivité chez Lepasterias Verrill, 1866 spp. en fonction du stade du cycle reproductif de l’étoile de mer. L’étendue de la tolérance de O. stellarum en eau de mer contenant des bactéries est de 2 PSU à 8°C et de 12,5 PSU à 25°C; le cilié tolère une gamme de températures de 3–27°C à 30 PSU. À 30 PSU, la croissance de la population de ciliés est maximale à 24°C et minimale à 3 et à 27°C. La fréquence du cycle de la vacuole contractile du cilié augmente aux salinités basses, ce qui indique qu’il y a un accroissement de la régulation du volume d’eau en fonction inverse de la salinité. Il est possible d’infecter expérimentalement des Leptasterias spp. mâles sains en injectant une culture d’O. stellarum dans les bras ou seulement en les plaçant dans une culture dans l’eau de mer ambiante au moment où les testicules ont atteint leur pleine taille; les ciliés n’envahissent cependant pas les tissus ovariens. Les gonopores constituent probablement la voie normale d’entrée d’O. stellarum dans les testicules des étoiles de mer mâles qui ont atteint la maturité sexuelle.

Document Type: Research Article

Publication date: 2007-02-01

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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