Showing papers by "Andrew J. Gooday published in 2011"

Testing the protozoan hypothesis for Ediacaran fossils: a developmental analysis of Palaeopascichnus

Abstract: The hypothesis that the Ediacara biota were giant protozoans is tested by considering the external morphology, internal organization, suggested fossil representatives and molecular phylogeny of the xenophyophores. From this analysis, we find no case to support a direct relationship. Rather, the xenophyophores are here regarded as a group of recently evolved Foraminifera and are hence unlikely to have a record from the Ediacaran Period. Further from the growth dynamics of Foraminifera, they are also unlikely to be related to the Palaeopascichnus organism. We also find significant distinctions in the growth dynamics of Palaeopascichnus and organisms usually referred to the Ediacara biota, such as Charnia and Dickinsonia. Developmental analysis of the Palaeopascichnus– central to the xenophyophore hypothesis – reveals unusual, protozoan features, including evidence for chaotic repair structures, for mergence of coeval forms, as well as complex bifurcations. These observations suggest that Palaeopascichnus is a body fossil of an unidentified protozoan but is unrepresentative of Ediacaran body construction, in general.

Xenophyophores (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic)

Abstract: Xenophyophores are abundant on a terrace of the lower Nazare Canyon (4300 m water depth) on the Portuguese margin. Here, the most abundant species, Reticulammina cerebreformis sp. nov., occurs in densities of up to 21 individuals/m2. This large species has a soft, friable hemispherical test up to 10 cm in diameter consisting of curved, sinuous plates (lamellae) that branch and anastomose. The plates are separated by deep furrows and other depressions to form a distinctive ‘brain-like’ structure. The outer test layer is thin, weakly cemented and is dominated by fine sediment particles; the internal xenophyae include a higher proportion of larger mineral grains. The second new species at the 4300-m site, Nazareammina tenera gen. et sp. nov., is much less common. The test is basically plate-like, but towards the interior it is perforated by oval spaces, which typically merge into complex system of bar-like features, sometimes with irregular excrescences. The granellare system (cell body and its organic envelope) is packed with tiny mineral grains of various sizes and shapes, including titanium-bearing particles. Also common at this deep site are clusters, with a maximum diameter up to 10 cm or occasionally more, of irregular tubes belonging to Aschemonella ramuliformis Brady 1884, a species previously known mainly from isolated tubes. Rather than being single individuals, these clusters comprise a large number of separate branched tubes. Finally, Syringammina fragillissima Brady 1883, a well-known species that is widely distributed on the NW European margin, occurred on steep sediment-covered slopes at a shallower (1555 m water depth) site in the upper canyon. Almost complete SSU rDNA gene sequences obtained from A. ramuliformis and R. cerebreformis confirm that these previous termxenophyophoresnext term are foraminifera. Together with two previously sequenced xenophophores (Shinkaia lindsayi Lecroq, Gooday, Tsuchiya, Pawlowski 2009 and Syringammina corbicula Richardson 2001), and the foraminiferan Rhizammina algaeformis, they constitute a clade within the radiation of monothalamous foraminifera. In situ photographs of R. cerebreformis and A. ramuliformis reveal no evidence of pseudopodia deployed onto the sediment surface. Instead, these species probably trap sediment within their complex, folded test surface (R. cerebreformis) or intercept suspended particles (A. ramuliformis).

New genera and species of monothalamous Foraminifera from Balaclava and Kazach’ya Bays (Crimean Peninsula, Black Sea)

Abstract: We describe two new genera and species of monothalamous Foraminifera from a coastal site in Balaclava Bay, Crimea. Nellya rugosa gen. and sp. nov. has an elongate, approximately oval test, 120–360 μm long, somewhat resembling a rice grain and with a single nipple-like apertural structure located at the distal end, which is often rather truncated. The wall is whitish, opaque, somewhat flexible and composed of jumbled mineral grains, mostly <10 μm in size, overlying an inner organic layer. Cedhagenia saltatus gen. and sp. nov. has an approximately lenticular test, 150–300 μm long, with a single aperture usually associated with a short, delicate, slightly flared extension of test. The wall is whitish, flexible, translucent with shiny highlights, and composed of a thin layer of plate-like mineral grains, mostly <5 μm in size, overlying an inner organic layer. In both N. rugosa and C. saltatus, the cytoplasm is finely granular, without stercomata. A third species, identified as Vellaria pellucidus Gooday and Fernando 1992 and closely resembling the type material of this species from the Vellar Estuary (India), occurs occasionally in our Balaclava Bay material. Samples from another Crimean Bay (Kazach’ya) yielded an undescribed species of Psammophaga that is most similar to a species from Southampton (UK). The agglutinated wall encloses a cell body that is packed with mineral grains. Analysis of the SSU rDNA sequences obtained from these four species confirmed the position of Psammophaga and Vellaria. Nellya is shown to be a sister group to Vellaria + Psammophaga clade but its position is not well resolved. Cedhagenia belongs to a very different clade of monothalamous foraminiferans, which includes also Ovammina and Cribrothalammina.

Biodiversity and distribution of the genus Gromia (Protista, Rhizaria) in the deep Weddell Sea (Southern Ocean)

Abstract: We present a survey of morphospecies of Gromia, a genus of testate protists, from bathyal and abyssal depths in the Weddell Sea and adjacent areas of the Southern Ocean. This material represents the most extensive and diverse available collection of deep-sea gromiids so far recorded. The twelve species, nine of which are undescribed, are recognized on the basis of morphological criteria, including the test size and shape, the appearance and structure of the oral capsule, and the characteristics of the test wall. Most species have a single oral capsule, which is circular in plan view with a conical nipple-like shape in lateral view. One morphospecies has three oral capsules. The appearance and structure of the wall displays great variability among Gromia species, ranging from very delicate and transparent with highly reflective highlights to relatively thick with distinct patterns of ridges covering the surface. More often, however, differences in wall structure are more subtle. Most morphospecies were distributed at bathyal depths along the continental margin, but one was sampled at ~4,800 m, representing the first record of an abyssal gromiid. Concurrent with findings from other regions of the World’s oceans, the Weddell Sea gromiids were mostly found in surficial sediments in areas of elevated organic input, suggesting that deep-sea gromiids are likely to play an important role in carbon cycling in bathyal eutrophic regions through the ingestion and degradation of fresh organic matter.

Intracellular mineral grains in the xenophyophore Nazareammina tenera (Rhizaria, Foraminifera) from the Nazaré Canyon (Portuguese margin, NE Atlantic)

Abstract: Xenophyophores, a group of large agglutinated foraminifera, are characterized by the presence of numerous intracellular barite grains, termed granellae, the function and origin of which is unclear. The recently described xenophyophore Nazareammina tenera (Gooday et al., in press), from abyssal depth (4300 m) in the Nazare Canyon contains an unusually dense concentration of mineral grains in its cytoplasm. Uniquely among known xenophyophores, the intracellular grains in this species comprise a variety of different mineral types in addition to barite. They exhibit a wide range of morphologies and energy dispersive X-ray analysis indicated that they include Ti-bearing minerals, many of them rod-shaped (probably rutile), as well as those containing Fe and Ti (possibly ilmenite and anatase), and Al and Si (probably clay minerals). While the function of intracellular particles in xenophyophores remains unclear, the presence of numerous particles of various types in the cytoplasm suggests that they originate from the sediment. This suite of intracellular mineral grains is completely different from that used to construct the agglutinated test of N. tenera, suggesting that this species is able to discriminate between different kinds of particles. A second xenophyophore species, Reticulammina cerebreformis (Gooday et al., in press), which is abundant at the same site as N. tenera, is devoid of intracellular particles, suggesting that their presence in N. tenera is a species-specific characteristic.

A new ‘saccamminid’ genus (Rhizaria: Foraminifera), from 4400 m water depth in the Nazaré Canyon (NE Atlantic)

Abstract: We describe Bithekammina occulta , a new monothalamous agglutinated foraminiferan (‘saccamminid’) collected in multicore samples at 4400 m on the terrace of the lower Nazare Canyon on the Portuguese margin. The test is spherical to oval, up to ~400 µm in length, with a simple circular aperture. The wall has a very smooth surface with a distinct sheen in reflected light. It is <10 µm thick and composed of very fine agglutinated plate-like clay particles and a thin inner organic layer. The most distinctive feature of the new species is that the test is contained within an agglutinated case (‘secondary test’) composed mainly of larger (10–50 µm) quartz grains. The case is equipped with a long, narrow tube that originates near the aperture of the inner test and presumably acts as a channel through which pseudopodia are deployed. Secondary agglutinated structures have been described in a number of foraminifera, but never before in a ‘saccamminid’.