A NOVEL LIFE-HISTORY IN AGLAOTHAMNION-DIAPHANUM-SP NOV (CERAMIACEAE, RHODOPHYTA) FROM BRITTANY AND THE BRITISH-ISLES

A diminutive species of Aglaothamnion (Ceramiaceae, Rhodophyta), A. diaphanum sp. nov., is described from Brittany (Atlantic France), the Isles of Scilly (off S.W. England) and western Ireland. Aglaothamnion diaphanum is confined to the sublittoral zone, where it grows almost exclusively on algae and sessile animals attached to hard substrata. Thalli are delicate, and branched distichously in one plane. The main axes are ecorticate but may form loose non-corticating rhizoidal filaments. The lateral branches bear a characteristic, regularly alternate distichous series of branchlets, the first of which is always adaxial. All vegetative cells are uninucleate. The majority of field-collected plants bear only bisporangia, but a few bisporangial plants also form spermatangia; some male plants and a single female specimen have been collected. The spermatangial branchlets consist of 3-5 spermatangial mother cells each bearing 2-4 spermatangia, which are constricted around a central nucleus. None of the U-shaped carpogonial branches showed any sign of fertilization, and the gametangia appear to be non-functional. The bisporangia are ovoid and contain two uninucleate spores separated by an oblique curved wall. The occurrence of bisporangia and the lack of adherent cortication distinguish A. diaphanum from two similar species, Aglaothamnion bipinnatum (P. Crouan et H. Crouan) Feldmann-Mazoyer and Aglaothamnion decompositum (J. Agardh) Halos. The life history in culture of French and Irish isolates of A. diaphanum consists of a series of bisporangial generations, a single plant of which also formed spermatangia. Apical cells of bisporophytes are haploid (n = c. 32), but the first division of meiosis, with chromosome pairing and crossing over, occurs in dividing bisporocytes. The germinating bispores are haploid. Endodiploidization may occur in the early stages of sporangium development, as in some phycomycete fungi, or in vegetative cells that subsequently give rise to bisporocytes. This is the first demonstration in the red algae of meiotic bisporangia on plants of which the apical cells, at least, are haploid.

Gayliella gen. nov in the tribe Ceramieae (Ceramiaceae, Rhodophyta) based on molecular and morphological evidence

On the basis of comparative morphology and phylogenetic analyses of rbcL and LSU rDNA sequence data, a new genus, Gayliella gen. nov., is proposed to accommodate the Ceramium flaccidum complex (C. flaccidum, C. byssoideum, C. gracillimum var. byssoideum, and C. taylorii), C. fimbriatum, and a previously undescribed species from Australia. C. transversale is reinstated and recognized as a distinct species. Through this study, G. flaccida (Kutzing) comb. nov., G. transversalis (Collins et Hervey) comb. nov., G. fimbriata (Setchell et N. L. Gardner) comb. nov., G. taylorii comb. nov., G. mazoyerae sp. nov., and G. womersleyi sp. nov. are based on detailed comparative morphology. The species referred to as C. flaccidum and C. dawsonii from Brazil also belong to the new genus. Comparison of Gayliella with Ceramium shows that it differs from the latter by having an alternate branching pattern; three cortical initials per periaxial cell, of which the third is directed basipetally and divides horizontally; and unicellular rhizoids produced from periaxial cells. Our phylogenetic analyses of rbcL and LSU rDNA gene sequence data confirm that Gayliella gen. nov. represents a monophyletic clade distinct from most Ceramium species including the type species, C. virgatum. We also transfer C. recticorticum to the new genus Gayliella.

Molecular systematics of Ceramium and Centroceras (Ceramiaceae, Rhodophyta) from Brazil

Morphological investigations identified 11 Ceramium Roth species, of the 18 previously reported from Brazil. Phylogenetic analyses of sequences of the chloroplast-encoded rbcL gene confirmed the presence of seven of these species. Three other species are reported from Brazil for the first time. Ceramium affine Setchell & Gardner and C. filicula Harvey ex Womersley were previously known only from the Pacific Ocean (Mexico and Australia, respectively). A new species, C. fujianum Barros-Barreto et Maggs sp. nov., is described here. Its general habit is similar to that of C. strictum sensu Harvey from Europe but it has one less periaxial cell than C. strictum; its cortical filament arrangement is closest to C. deslongchampsii Chauvin ex Duby, also from Europe, but whorled tetrasporangia partially covered by cortical cells differ strikingly from the naked protruding tetrasporangia of C. deslongchampsii. Ceramium species in which each periaxial cell cuts off transversely only a single basipetal cell formed a robust clade. The genus Ceramium as represented in Brazil is not monophyletic with respect to Centroceras Kutzing and Corallophila Weber-van Bosse; Ceramium nitens, which has axial cells completely covered by rounded cortical cells formed by acropetal and basipetal filaments, did not group with any Ceramium clade but was weakly allied to a species of Corallophila. All three Brazilian Centroceras sequences were attributed to a single species, C. clavulatum.

The genus Pikea (Dumontiaceae, Rhodophyta) in England and the North Pacific: Comparative morphological, life history, and molecular studies

A Pikea species attributed to Pikea californica Harvey has been established in England since at least 1967. Previously, this species was believed to occur only in Japan and Pacific North America. Comparative morphological studies on field-collected material and cultured isolates from England, California, and Japan and analysis of organellar DNA restriction fragment length polymorphisms, detected using labeled organellar DNA as a non-radioactive probe, showed that English Pikea is conspecific with P. californica from California. Both populations consist of dioecious gametophytes with heteromorphic life histories involving crustose tetrasporophytes; 96% of organellar DNA bands were shared between interoceanic samples. A second dioecious species of Pikea, P. pinnata Setchell In Collins, Holden et Setchell, grows sympatrically with P. californica near San Francisco but can be distinguished by softer texture, more regular branching pattern, and elongate cystocarpic axes. Pikea pinnata and P. californica samples shared 49-50% of organellar DNA bands, consistent with their being distinct species. Herbarium specimens of P. robusta Abbott resemble P. pinnata in some morphological features but axes are much wider; P. robusta may represent a further, strictly subtidal species but fertile material is unknown. Pikea thalli from Japan, previously attributed to P. californica and described here as Pikea yoshizakii sp. nov., are monoecious and show a strikingly different type of life history. After fertilization, gonimoblast filaments grow outward through the cortex and form tetrasporangial nemathecia; released tetraspores develop directly into erect thalli. Tetrasporoblastic life histories are characteristic of certain members of the Phyllophoraceae but were previously unknown in the Dumontiaceae. Japanese P. yoshizakii shared 55 and 56% of organellar DNA bands with P. californica and P. pinnata, respectively phylogenetic analysis indicated equally distant relationships to both species. Pikea yoshizakii or a closely similar species with the same life history occurs in southern California and Mexico.

A Silurian armoured aplacophoran and implications for molluscan phylogeny

The Mollusca is one of the most diverse, important and well-studied invertebrate phyla; however, relationships among major molluscan taxa have long been a subject of controversy(1-9). In particular, the position of the shell-less vermiform Aplacophora and its relationship to the better-known Polyplacophora (chitons) have been problematic: Aplacophora has been treated as a paraphyletic or monophyletic group at the base of the Mollusca(3,6,8), proximate to other derived clades such as Cephalopoda(2,3,10), or as sister group to the Polyplacophora, forming the clade Aculifera(1,5,7,11,12). Resolution of this debate is required to allow the evolutionary origins of Mollusca to be reconstructed with confidence. Recent fossil finds(13-16) support the Aculifera hypothesis, demonstrating that the Palaeozoic-era palaeoloricate 'chitons' included taxa combining certain polyplacophoran and aplacophoran characteristics(5). However, fossils combining an unambiguously aplacophoran-like body with chiton-like valves have remained elusive. Here we describe such a fossil, Kulindroplax perissokomos gen. et sp. nov., from the Herefordshire Lagerstatte(17,18) (about 425 million years BP), a Silurian deposit preserving a marine biota(18) in unusual three-dimensional detail. The specimen is reconstructed three-dimensionally through physical-optical tomography(19). Phylogenetic analysis indicates that this and many other palaeoloricate chitons are crown-group aplacophorans.

Coleoptera and microbe biomass in Antarctic Dry Valley paleosols adjacent to the Inland Ice: Implications for Mars

Bulk paleosol samples collected from a Middle to Early Miocene moraine in the New Mountain area of the Dry Valleys, Antarctica, yielded Coleoptera exoskeletons and occasional endoskeletons showing considerable diagenetic effects along with several species of bacteria, all lodged in a dry-frozen but salt-rich horizon at shallow depth to the land surface. The till is at the older end of a chronologic sequence of glacial deposits, thought to have been deposited before the transition from wet-based to cold-based ice (similar to 15 Ma), and hence, entirely weathered in contact with the subaerial atmosphere. It is possible, though not absolutely verifiable, that the skeletons date from this early stage of emplacement having undergone modifications whenever light snowmelt occurred or salt concentrations lowered the freezing temperature to maintain water as liquid. Correlation of the Coleoptera species with cultured bacteria in the sample and the likelihood of co-habitation with Beauveria bassiani found in two adjacent, although younger paleosols, leads to new questions about the antiquity of the Coleoptera and the source of N and glucose from chitinase derived from the insects. The skeletons in the 831 section may date close to the oldest preserved chitin (Oligocene) yet found on Earth. While harsh Martian conditions make it seemingly intolerable for complex, multicellular organisms such as insects to exist in the near-surface and subaerially, life within similar cold, dry paleosol microenvironments (Cryosols) of Antarctica point to life potential for the Red Planet, especially when considering the relatively diverse microbe (bacteria and fungi) population. (C) 2011 Elsevier Ltd. All rights reserved.