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1 October 2019 Active Floating with Buoyancy of Pseudopodia Versus Passive Floating by Hydrodynamic Drag Force: A Case Study of the Flat-Shaped Spumellarian Radiolarian Dictyocoryne
Ryo Ichinohe, Yuta Shiino, Toshiyuki Kurihara, Naoko Kishimoto
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Abstract

It has been suggested that the pseudopodia of radiolarians play a role in controlling buoyancy for floating behaviour. To understand the function of pseudopodia in terms of planktonic capability, we performed culture experiments on the flat-shaped radiolarian Dictyocoryne. A glass cell, a stereomicroscope and an X-Y-Z stage were used to observe the behaviour of Dictyocoryne from a lateral view. Under static conditions, Dictyocoryne grounded on the bottom of the glass cell extended pseudopodia from both sides of the flat disc surface. Subsequently, these individuals rose slightly by a length equal to that of the extended pseudopodia but remained attached to the bottom. These results suggest that Dictyocoryne lacks the ability to surface by obtaining buoyancy through the emergence of pseudopodia. Under conditions of convection flow, Dictyocoryne moved in the downstream direction only when pseudopodia were completely extended. When the convection flow moved upward, the individuals moved with the flow to just under the surface. In addition, convection flow changed the direction of a long, thick pseudopodium, called the axoflagellum, to be parallel with the flow. Consequently, the axoflagellum was always oriented towards the downstream side, being the disc face in the axoflagellum side on the upturn. Given that the flat-shaped spumellarians have symbiotic algae inside their cells, their unique planktonic capability leads to the stable efficiency of the algal photosynthesis.

© by the Palaeontological Society of Japan
Ryo Ichinohe, Yuta Shiino, Toshiyuki Kurihara, and Naoko Kishimoto "Active Floating with Buoyancy of Pseudopodia Versus Passive Floating by Hydrodynamic Drag Force: A Case Study of the Flat-Shaped Spumellarian Radiolarian Dictyocoryne," Paleontological Research 23(4), 236-244, (1 October 2019). https://doi.org/10.2517/2018PR023
Received: 31 March 2018; Accepted: 22 October 2018; Published: 1 October 2019
KEYWORDS
behaviour
holoplankton
hydrodynamics
protist
Spumellaria
symbiosis
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