Fig. 1. Chloroplasts of foraminiferal symbionts. Gulf of Aqaba. TEM graphs courtesy S. Reber-Leutenegger. A: Bacillarian (diatom) symbionts below lateral chamber wall, housed in eggholders, below pore mouths, of Amphistegina lobifera Larsen. x 5,000. B: dinophycean (dinoflagellate) symbiont of Amphisorus hemprichii Ehrenberg. Note sections of short flagellae (arrows) permitting active movement of the symbiont within the lacunar system of the host, to regulate its access to light. The nucleus with its (polyploid) chromosomes visible during the interphase unusual among eucaryotes but characteristic for dinophyceans. x 10,000. C: rhodophycean (red algal) symbiont of Peneroplis planatus (Fichtel et Moll). x 12,000. D: Bacillarian symbiont of Assilina ammonoides (Gronovius), ultrathin section oblique-tangential to the lateral surface of achamber. Note the loose stacking of the thylacoids in the chloroplast, a characteristic of symbionts of Assilina. X 8,000. E: Elphidium craticulatum (Fichtel et Moll), ultrathin section through a protoplast of a chamber including one of its retral processes (double arrow), showing free chloroplasts in the host chamberplasm, a characteristic of symbiont husbandry. x 4,000. F: Rhodophycean symbionts of Peneroplis planatus (Fichtel et Moll) from Elba in the Mediterranean. Note starch grains covering the pyrenoid and filling most of the symbiont's mass. The starch grains may also appear as free grains in the host chamber plasm and represent seasonal food storage for the host. x 4,000. bD: basal pore disc; cpl: chloroplast; flag: flagellum with its base; ilD: interlamellar disc of pore; m: mitochondrium; n: nucleus; OL: organic lining; p: pore; Pl: plasmalemma; ppl: pore plug; pyr: pyrenoid; spl: (mineralized) sieve plate; tyl: thylacoid; v: vacuoles; (Hottinger, 2006; fig. 30  CC/BY-NC-SA)
- according to Hottinger (2006):
SYMBIOSIS - in foraminifera: algal cells living (as symbionts) within the foraminiferal cytoplasm in a mutualistic relationship with their host. The symbionts actively photosythesize and reproduce asexually in the host cell. They are engaged in recycling nutrients. They live either in vacuoles of the host cytoplasm and are displaced passively by the host's protoplasmic streaming, or are found in the lacunar system of the host cell within which they may move actively using their shortened flagella to regulate the amount of their irradiation by sunlight so as to avoid photoinhibition. During the asexual reproduction of the host, each offspring inherits a small number of symbionts from the mother cell. But after sexual reproduction, the foraminiferal zygote must take up symbionts from its ambient environment.
Hottinger (2006), Illustrated glossary of terms used in foraminiferal research. Carnets de Géologie, Memoir 2, ISSN 1634-0744
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