Structure of Organic Spines in the Rhizarian Protist Belonocystis tubistella Rainer, 1968, and a Description of Belonocystis quadrangularis n. sp. (Cercozoa, Insertae Sedis)

Kenneth H. Nicholls


Several Ontario (Canada) populations of the “heliozoan-like” protist Belonocystis Rainer, 1968 were studied to help elucidate the taxonomic position of this genus relative to other rhizarian protists with fine pseudopodia. The Ontario material presently includes two distinct species – B. tubistella Rainer and B. quadrangularis n. sp., described here as a new species based on cell morphology and microstructure of the spiny investiture encasing its cell. The organic nature of the spiny structures of both species has been confirmed by their dissolution in 6% sodium hypochlorite solution. Median cell diameters of B. tubistella and B. quadrangularis were 10.5 μm and 7 μm, respectively. As revealed by transmission electron microscopy, the spine bases in B. tubistella consisted of a complex structure of four curved ribs interconnected by a membranous sheet replete with closely-appressed, large circular to elliptical pores, while in B. quadrangularis the spine bases consisted of a simple four-cornered “pyramid” of struts that supported the main shaft of the spine. These findings strengthen the status of the genus Belonocystis and it placement outside the realm of the Centrohelida and Rotosphaerida.

Słowa kluczowe: Clathrulinidae, Desmothoracida, Rhizaria, pseudoheliozoa, spined protist

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