. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CYTOSKELETON IN A SYNCYTIAL SPONGE 253. MF Figure 9. An illustration summarizing the cytoskeletal architecture in a 24-h adhered aggregate of Rhah- dix'alvptus. Microfilament bundles IMF) traverse the basal layer of aggregates. At the periphery, microfilament bundles give rise to giant actin-dense rods (R). which extend through lamellipodia (LM) to anchor the preparation to the substrate. Inside a cutaway of the plasma membrane (PM), a stream is exposed showing bundles of microtubules (MT) with associated nuclei (Ns), mitoch
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. CYTOSKELETON IN A SYNCYTIAL SPONGE 253. MF Figure 9. An illustration summarizing the cytoskeletal architecture in a 24-h adhered aggregate of Rhah- dix'alvptus. Microfilament bundles IMF) traverse the basal layer of aggregates. At the periphery, microfilament bundles give rise to giant actin-dense rods (R). which extend through lamellipodia (LM) to anchor the preparation to the substrate. Inside a cutaway of the plasma membrane (PM), a stream is exposed showing bundles of microtubules (MT) with associated nuclei (Ns), mitochondria (M), and vesicles (V). Also adjacent to the microtubules are groups of archaeocytes (AR). with their own nuclei (Nar). connected to each other and the rest of the cytoplasm by perforate plugged junctions (PJ). less, the likelihood that streaming occurs in the intact sponge is borne out by observations of streaming in re- generating fragments of the whole animal (Leys and Mackie, 1994). Video microscopy of aggregates suggests that streaming, or the microtubule network involved in streaming, may play a role in organizing the tissues of intact sponges, for instance by influencing the distribution and clustering of archaeocytes, spherulous cells, choano- blasts, and collar bodies. Archaeocytes do not appear to play the central role during aggregation in Rhabdocalyptus that they do in cellular sponges (Buscema el 1980). Because adults of this species can be up to 2 m in length, and assuming that the trabecular tissues are continuous throughout the animal, Rhabdocalyptus must represent one of the largest syncytial organisms within the metazoa. The evidence presented in this paper shows that adhered aggregates of Rhabdocalyptus possess a unique cellular motile system and a giant cytoskeleton. The observations strongly support the view that most of the cytoplasm in hexactinellids constitutes a multinucleate syncytium. It now seems clear that hexactinellids differ substantia
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
