FUNCTIONAL MORPHOLOGY AND SPECIES CHARACTERISTICS OF A LARGE, SOLITARY RADIOLARIANPHYSEMATIUM MUELLERI

Abstract

Physematium spp. and related genera of radiolaria (e.g., Thalassolampe and Actissd) are characterized by a large, limpid spherical cell body varying in cytoplasmic compactness, but characteristically possessing numerous small (ca. 3 nm dia.) symbionts held in fine radiating axopodia surrounding the large central capsulum. An analysis of the cytoplasmic organization of Physematium muelleri suggests that this organism has adapted to a pelagic existence by increasing surface area to enhance prey capture while conserving biomass through the development of a large internally alveolate, spheroidal cell possessing fluid-filled spaces. The thin capsular wall is supported by a network of cytoplasmic strands emanating from the perinuclear region of the intracapsulum. The fine structural organization of the cytoplasm, composition and thickness of the central capsular wall, and the amount and kind of material deposited within the perinuclear envelope appear to be more significant taxonomic discriminating characteristics than the number or kind of siliceous spicules produced surrounding the central capsulum. The possible phylogenetic relationships among some genera related to Physematium and the functional morphology of the large, fluid-filled central capsule of close relatives are presented.

Large Phaeodaria in the twilight zone: Their role in the carbon cycle

“…Shallow 100 m 150 m λ tot (m −1 ) 0-100 m 0-150 m < 100 m 100-150 m λ Aul (m −1 ) (Anderson et al 1986), they have not been observed for Phaeodaria (Anderson et al 1986;. Furthermore, the results from the phaeodarian peak encountered on our P1106 cruise offer powerful constraints for testing this hypothesis.…”

“…Increasing its collection area sufficiently to meet its carbon supply (at a C : V ratio of 80 μ g C mm −3 ) would require a ~ ×80 increase in area or ~ ×9 increase in ESD. While extensive pseudopodial networks have been observed in some Rhizaria (Anderson et al ), they have not been observed for Phaeodaria (Anderson et al ; Nakamura and Suzuki ). Furthermore, the results from the phaeodarian peak encountered on our P1106 cruise offer powerful constraints for testing this hypothesis.…”

“…We have assumed that the collection area of Aulosphaeridae is equivalent to the area of a circle defined by the maximum extent of its siliceous spicules (thus assuming that it is larger than the diameter used for biovolume). However, some solitary polycystine radiolarians produce pseudopodial extensions that allow them to increase their effective collection area (Anderson and Botfield ; Anderson et al ). Increasing its collection area sufficiently to meet its carbon supply (at a C : V ratio of 80 μ g C mm −3 ) would require a ~ ×80 increase in area or ~ ×9 increase in ESD.…”