The enigmatic, deep-sea, organic-walled genera Chitinosiphon, Nodellum and Resigella (Protista, Foraminifera): a taxonomic re-evaluation

Gooday, Andrew J., Kamenskaya, Olga E. and Kitazato, Hiroshi (2008) The enigmatic, deep-sea, organic-walled genera Chitinosiphon, Nodellum and Resigella (Protista, Foraminifera): a taxonomic re-evaluation. Systematics and Biodiversity, 6 (3), 385-404. (doi:10.1017/S1477200008002776).

Abstract

Using a morphology-based approach, we explore the relationships between three poorly understood species of organic-walled Foraminifera. Thalmann and Bermudez (1954) described Chitinosiphon rufescens as the type species of a new monotypic genus which they compared to the tubular agglutinated foraminiferan Bathysiphon. Loeblich and Tappan (1964), however, considered C. rufescens to be identical to Reophax membranacea Brady 1879, type species of another organic-walled genus, Nodellum. Based on a re-examination of the type specimens of both species, new material of C. rufescens from the Lost City hydrothermal field, and new material of N. membranacea from the NE Atlantic and Pacific Oceans, we show that these two deep-sea species are distinguished by the following features. (1) Chitinosiphon rufescens lacks the distinct, regular constrictions that divide the tubular test of N. membranacea into a series of segments. (2) The proloculus is spindle-shaped in C. rufescens but sub-cylindrical in N. membranacea. (3) A distinctive, pocket-like invagination is developed at the base (proximal end) of the proloculus in N. membranacea but not in C. rufescens. However, a series of undescribed species which occur in deep-sea sediments blur the distinction between the two genera. We therefore adopt a conservative position and regard Chitinosiphon as a junior synonym of Nodellum. We also examined the holotype and new material of Nodellum moniliforme Resig, 1982, the type species of Resigella Loeblich and Tappan, 1984, in which the organic-walled test comprises a series of bulbous chambers. This species exhibits a basal invagination, identical to the feature present in Nodellum membranacea. These three remarkable species are united by the basically tubular test and the nature of the test wall which is largely organic, brownish in colour, and exhibits no internal structure when broken sections are examined by SEM. The surface of the organic test of Nodellum rufescens from Lost City is strewn with tiny (?1 ?m), needle-shaped mineral particles, visible only by SEM. More equidimensional, micron-sized particles are present in the other two species. We agree with Thalmann and Bermudez (1954) that N. rufescens is related to tubular agglutinated taxa such as Bathysiphon. Resigella may have similar affinities, although this needs to be tested using molecular approaches.

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