. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SENESCENCE IN A COLONIAL ASCIDIAN 375. Figure 6. Further ultrastructural alterations in zooids at day 3 of nonrandom senescence, (a) Individual cell with prominent lipid inclusion found in blood space of /.ooid. Such cells are found randomly dispersed in blood and viscera throughout the dorsoventral plane of individual zooids. (b) Cross-section through the brush border of the gastric epithelium reveals fused microvilli. These cells do not yet display any disruption of the nuclear membrane, but some loss of cytoplasinic densi
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. SENESCENCE IN A COLONIAL ASCIDIAN 375. Figure 6. Further ultrastructural alterations in zooids at day 3 of nonrandom senescence, (a) Individual cell with prominent lipid inclusion found in blood space of /.ooid. Such cells are found randomly dispersed in blood and viscera throughout the dorsoventral plane of individual zooids. (b) Cross-section through the brush border of the gastric epithelium reveals fused microvilli. These cells do not yet display any disruption of the nuclear membrane, but some loss of cytoplasinic density can be observed (large black arrowheads), (c) Phagocyte found in the branchial basket with multiple phagolysosomes. (d) Longitudinal section of the endostyle. near the ventral sinus, reveals prominent membrane whorls indicative of autophagy. However, the tight junctions have remained intact. Abbreviations: ap. autophagic vacuoles; mv. microvilli: ec, engulfed cell; n, nucleus; pi. phagolysosome; pv, perivisceral epithelium; tj. tight junctions. Scale bars = 1 (xm. notype in this species was defined by characteristic mor- phological changes that were identical from colony to col- ony, and which began with the systemic constriction of the colonial vasculature. followed by cellular necrosis as an end-point. Macroscopic, senescence-associated changes similar to the ones reported here have been documented in field-grown B. schlosseri colonies (Brunetti. 1974; Chad- wick-Furman, 1995a). For instance, Brunetti (1974) de- scribed a mortality process with rapid onset, in B. schlosseri colonies from the Venetian Lagoon (Italy). The features of this process included slowing of blood flow: storage of pigment cells within blood vessels, ampullae, and zooid body wall; inability of zooids to form complete systems; dilation of siphons: and separation of buds from the parent zooids. The concordance between our macroscopic obser- vations of laboratory colonies and those resulting from field w
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
