Chemico-structural evolution of linguloid brachiopod shells

Chemico-structures of shells representing all families presently assigned to the Linguloidea have undergone significant transformations since the Early Cambrian. Superficial hemispherical to hemi-ellipsoidal pits on the larval and/or mature shells are interpreted as casts of deformable, membrane-bound vesicles of mucus or rigid vesicles of glycoproteins or GAGs with thickened coats. Flat-bottomed, sub-circular imprints characterize acrotheloids and many acrotretides, and could be impressions of biconvex tablets of apatite like those exocytosed within the primary layer of the obolid ‘Lingulella’? antiquissima, whilst the rhomboidal imprints of the Paterula shell could have held tablets of proteinaceous silica like those of living discinid larvae. The ancestral fabric of the linguloid secondary layer was probably composed of rubbly and virgose sets, but trellised rods of apatite (baculation) are characteristic of most linguloids and also acrotheloids. This condition was suppressed in shells identified as ‘Lingula’ from at least the Early Carboniferous to the present day. In early Palaeozoic acrotretides and lingulellotretids, columnar and camerate fabrics evolved in place of baculation. Baculation in Discinisca tenuis and Glottidia pyramidata is associated with the amino acids glutamic acid, glycine, alanine, arginine and proline which may be components of an organic polymer axial to baculate accretion.     

Genetic structure of three populations of the 'living fossil' brachiopod Lingula from Queensland, Australia

An electrophoretic survey of enzyme variation demonstrates that the genomes of three populations of the inarticulate brachiopod Lingula contain a higher level of variability than the average for marine, tropical invertebrates, and for other brachiopods. Genetic distances between populations from localities up to 1200 km apart were very small, indicating that the populations belong to a single species, L. anatina Lamarck. These data suggest that larval dispersal is capable of maintaining a homogeneous gene pool over this range. It is predicted that the dispersal mechanism is sufficiently efficacious to ensure gene-flow throughout most of the Indo-West Pacific distribution of Lingula. Further investigations of genetic distance should support the hypothesis, based on studies of adult and larval morphology, that many presently recognized species should be reassigned to L. anatina.     

Mineral phase in linguloid brachiopod shell: Lingula adamsi

The linguloid brachiopod shell family has been the focus of several studies because of the similarity in the composition of the mineral phase of these shells to that of human bone. However, ultrastructural features of Lingula shells have not yet been fully demonstrated at high magnification using Transmission Electron Microscopy (TEM) and Electron Diffraction. Ultrastructural characterization of the mineral phase in Lingula shells will improve our understanding of the biomineralization processes and mineral/organic interaction in more complex systems such as in bone or in other human mineralized tissues. In this study, the mineral phase of Lingula adamsi was characterized using a combination of ultrastructural and crystallographic techniques. The results showed that L. adamsi shells consist of apatite crystals of varying size, shape, and orientation in different areas of the shell. The c-axis of apatite was parallel to the shell surface and crystals were organized in different laminae. Compared to trabecular bovine bone, L. adamsi shells demonstrated a higher crystallinity and a lower amount of carbonate and organic compounds. This study therefore demonstrated how dissimilar organic matrix between L. adamsi shell and trabecular bone can modify the ultrastructural characteristics of apatite crystals in these two biomineralized tissues.     

Chemico-structural phylogeny of the discinoid brachiopod shell

Stratiform shells of living discinids are composed of membranous laminae and variously aggregated, protein-coated granules of apatitic francolite supported by proteinaceous and chitinous nets in glycosaminoglycans (GAGs) to form laminae in rhythmic sets. The succession is like that of living lingulids but differs significantly in the structure of the periostracum, the nature of baculate sets and in its organic composition. In particular, discinids have a higher level of amino acids although with relatively lower acidic and higher basic concentrations; and their overall lower organic content is owing to lower levels of hydrophilic components, like GAGs and chitin. The organic constituents are not completely degraded during fossilization; but data are presently too meagre to distinguish between linguloid and discinoid ancestries. Many differences among three of the four described extant genera emanate from transformations with a long geological history. Pelagodiscus is characterized by regular, concentric rheomorphic folding (fila) of the flexible periostracum and the plastic primary layer and by sporadically developed hemispherical imprints of periostracal vesicles. Both features are more strikingly developed in Palaeozoic discinids. In the oldest discinid, the Ordovician Schizotreta, and the younger Orbiculoidea and related genera, vesicles were persistent, hexagonal close-packed arrays fading out over fila. They must have differed in composition, however, as the larger vesicles of Schizotreta were simple (possibly mucinous), whereas the smaller vesicles of Orbiculoidea and younger genera were composites of thickly coated spheroids, possibly of lipoproteins, which survive as disaggregated relicts in Pelagodiscus. Baculate sets within the secondary layer are also less well developed in living discinids, being incipient in Pelagodiscus and restricted to the dorsal valve of Discinisca. The trellised rods (baculi) with proteinaceous cores are composed of pinacoids or prisms of apatite, depending on whether they are supported by chitinous nets or proteinaceous strands in GAGs. This differentiation occurred in Schizotreta but in that stock (and Trematis) the baculate set is symmetrical with baculi subtended between compact laminae, whereas in younger and post-Palaeozoic species the outer bounding lamina(e) of the set is normally membranous and/or stratified. The most striking synapomorphy of living discinids is the intravesicular secretion of organsiliceous tablets with a crystalline habit within the larval outer epithelium and their exocytosis as a close- or open-packed, transient, biomineral cover for larvae. Canals, on the other hand, are homologous with those pervading lingulid shells. Both systems interconnect with chitinous and proteinaceous sets and have probably always served as vertical struts in an organic scaffolding supporting the stratiform successions. A phylogenetic analysis based mainly on shell structure confirms the discinoids as the sister group of the linguloids but, contrary to current taxonomic practice, also supports the inclusion of acrotretoids within a ''discinoid'' clade as a sister group to the discinids.     

Differences in species diversity of Monogenea between the Pacific and Atlantic Oceans

Data from five extensive surveys each in the Pacific and Atlantic Oceans show that relative species diversity (number of parasite species per host species) of gill Monogenea of coastal marine fishes is greater in the northern and southwestern Pacific than in the northeastern and central- and southwestern Atlantic. Relative species diversity is markedly lower in the cold northeastern Atlantic than in the warmer parts of the Atlantic examined, and in the northern Pacific than in the warm southwestern Pacific. The difference between the northern Pacific and Atlantic is entirely or almost entirely due to a much greater number of species of Gyrodactylidae in the northern Pacific. A species-area relationship cannot explain the difference, because the area of the northern Pacific is not larger than that of the northern Atlantic and because Gyrodactylidae are cold-water forms which cannot have immigrated from warmer seas. The difference is tentatively explained by an evolutionary time hypothesis: more species of Gyrodactylidae have accumulated in the much older Pacific than in the Atlantic Ocean. Alternatively, an ecological time hypothesis may explain the difference: ice sheets during the last glaciation covered much more of the continental shelf in the northern Atlantic than in the northern Pacific, possibly extinguishing more Monogenea in the former than in the latter Ocean.     

Stomatopods (Crustacea: Hoplocarida) from the Gulf of Tehuantepec, Mexico

A total of 1,173 specimens of Stomatopoda were captured in 27 localities at different depths (20 to 73 m) during three oceanographic cruises in the Mexican Pacific along the continental shelf of the states of Oaxaca and Chiapas. Seven species were identified of the families Eurysquillidae, Lysiosquillidae and Squillidae. Squilla hancocki and Squilla parva were the most abundant species and the most frequently found together. The relationships between total length and carapace length were obtained for these species, which show that males of S. hancocki have a longer carapace length than females having the same total length, whereas for S. parva the opposite occurs. Larger sizes than previously reported were obtained for Lysiosquilla panamica and Squilla mantoidea. Squilla bigelowi was recorded for the first time in the Gulf of Tehuantepec. All the species were found in the intermediate platform (25-60 m); E. veleronis, S. hancocki and S. parva extended their distributions to the external platform (60-120 m), and S. hancocki and S. parva reached the circalittoral zone (10-25 m).     

Land barriers and open oceans: effects on gene diversity and population structure in Avicennia germinans L. (Avicenniaceae)

Avicennia germinans L. is a widespread mangrove species occupying the west coast of Africa and the Atlantic and Pacific coasts of the Americas from the Bahamas to Brazil and Baja California to Peru. An amplified fragment length polymorphism (AFLP) molecular analysis was carried out to assess genetic architecture within this species and to evaluate the effects of the Atlantic Ocean and the Central American Isthmus (CAI) on population and regional genetic diversity and differentiation. In total, 349 polymorphic AFLP fragments were identified among 144 individuals from 14 populations from the east Atlantic, west Atlantic and east Pacific. Levels of genetic diversity varied considerably among populations, but were generally higher in populations from the east Atlantic. Regional differentiation between the Pacific coast and Atlantic populations was greater than between east and west Atlantic populations, suggesting that the CAI has had an important influence on population genetic structure in this species. The lower level of divergence of east Atlantic from west Atlantic populations suggests some dispersal across the Atlantic Ocean, although migration rates are probably low; Nm from GST equal to 0.41 and accumulation of private and rare alleles in the east Atlantic. Population differentiation did not appear to follow an isolation by distance model and has probably resulted from complex patterns of population bottlenecks, and founder events due to landscape changes during the Pleistocene, particularly in the west Atlantic. The molecular data provide no support for the treatment of east Atlantic populations as a separate species A. africana.     

Phylogenetic relationships of tropical western Atlantic snappers in subfamily Lutjaninae (Lutjanidae: Perciformes) inferred from mitochondrial DNA sequences

Phylogenetic relationships among 20 nominal species of tropical lutjanine snappers (Lutjanidae) (12 from the western Atlantic, one from the eastern Pacific, and seven from the Indo‐Pacific) were inferred based on 2206 bp (712 variable, 614 parsimony informative) from three protein‐coding mitochondrial genes. Also included in the analysis were DNA sequences from two individuals, identified initially as Lutjanus apodus, which were sampled off the coast of Bahia State in Brazil (western Atlantic), and from three individuals labelled as ‘red snapper’ in the fish market in Puerto Armuelles, Panama (eastern Pacific). Bayesian posterior probabilities and maximum‐likelihood bootstrap percentages strongly supported monophyly of all lutjanines sampled and the hypothesis that western Atlantic lutjanines are derived from an Indo‐Pacific lutjanine lineage. The phylogenetic hypothesis also indicated that oceans where lutjanines are distributed (western Atlantic, eastern Pacific, and Indo‐Pacific) are not reciprocally monophyletic for the species distributed within them. There were three strongly supported clades that included all western Atlantic lutjanines: one included six species of Lutjanus from the western Atlantic, two species of Lutjanus from the eastern Pacific, and the monotypic genera Rhomboplites and Ocyurus (western Atlantic); one that included three, probably four, species of Lutjanus in the western Atlantic; and one that included Lutjanus cyanopterus (western Atlantic), an unknown species of Lutjanus from the eastern Pacific, and three species of Lutjanus from the Indo‐Pacific. Molecular‐clock calibrations supported an early Miocene diversification of an Indo‐Pacific lutjanine lineage that dispersed into the western Atlantic via the Panamanian Gateway. Divergent evolution among these lutjanines appears to have occurred both by vicariant and ecological speciation: the former following significant geographic or geological events, including both shoaling and closure of the Panamanian Gateway and tectonic upheavals, whereas the latter occurred via phenotypic diversification inferred to indicate adaptation to life in different habitats. Taxonomic revision of western Atlantic lutjanines appears warranted in that monotypic Ocyurus and Rhomboplites should be subsumed within the genus Lutjanus. Finally, it appears that retail mislabelling of ‘red snapper’ in commercial markets extends beyond the USA. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 102 , 915–929.     

Origin, diversification, and historical biogeography of the genus Trachurus (Perciformes: Carangidae)

We addressed phylogenetic relationships in the genus Trachurus using cytochrome b gene and D-loop sequences. The trees showed five groups: (1) the Southwest Pacific species (T. japonicus, T. novaezelandiae, and T. declivis); (2) The Mediterranean Sea and Eastern Atlantic species (T. mediterraneus); (3) The Atlantic Ocean species (T. lathami and T. trecae); (4) Eastern Atlantic species (T. trachurus and T. capensis); and (5) a group of highly mobile pelagic species, two from the Eastern Pacific (T. symmetricus and T. murphyi) and one from the Eastern Atlantic (T. picturatus). The phylogeny based on Cyt b, supports the molecular clock hypothesis and our results agree with the reported fossil indicating that the origin of this genus occur when the Thetys Sea closed (around 18.4 MYA). In addition, a very slow neutral substitution rate is reported identified only two periods of maximum diversification: the first occurring between 18.4 and 15.0 MYA and the second between 8.4 MYA and present day.     

Species-level phylogeography and evolutionary history of the hyperdiverse marine gastropod genus Conus

Phylogenetic and paleontological analyses are combined to reveal patterns of species origination and divergence and to define the significance of potential and actual barriers to dispersal in Conus, a species-rich genus of predatory gastropods distributed throughout the world's tropical oceans. Species-level phylogenetic hypotheses are based on nucleotide sequences from the nuclear calmodulin and mitochondrial 16S rRNA genes of 138 Conus species from the Indo-Pacific, eastern Pacific, and Atlantic Ocean regions. Results indicate that extant species descend from two major lineages that diverged at least 33 mya. Their geographic distributions suggest that one clade originated in the Indo-Pacific and the other in the eastern Pacific + western Atlantic. Impediments to dispersal between the western Atlantic and Indian Oceans and the central and eastern Pacific Ocean may have promoted this early separation of Indo-Pacific and eastern Pacific + western Atlantic lineages of Conus. However, because both clades contain both Indo-Pacific and eastern Pacific + western Atlantic species, migrations must have occurred between these regions; at least four migration events took place between regions at different times. In at least three cases, incursions between regions appear to have crossed the East Pacific Barrier. The paleontological record illustrates that distinct sets of Conus species inhabited the Indo-Pacific, eastern Pacific + western Atlantic, and eastern Atlantic + former Tethys Realm in the Tertiary, as is the case today. The ranges of <1% of fossil species (N=841) spanned more than one of these regions throughout the evolutionary history of this group.     

Burrowing of the lingulid brachiopod Glottidia pyramidata: its ecologic and paleoecologic significance

Contrary to popular assumption, the pedicle of Glottidia is not its principal burrowing organ. The brachiopod props itself up with the pedicle and enters the sediment with the valves leading, anterior end first. The pedicle trails behind. Burrowing is accomplished by cyclical valve motions: rotary, sliding, and gaping movements are used. Rapid valve closure ejects water from the mantle cavity to loosen the sediment. The lateral setae convey mucus-bound sand posteriorly (upwards). X-radiography shows that the burrows are U-shaped: in a few hours, the animal reappears in feeding position with the anterior end pointing out of the sediment and the pedicle extending down into the burrow. This burrowing process explains the substrate preferences of lingulids. The thick. closely spaced setae are adapted for burrowing. The spacing between individuals is increased, suggesting competition for food.     

Review of the Australian aphrophorid spittlebugs (Hemiptera: Aphrophoridae)

Abstract A review of the Aphrophoridae (Hemiptera: Auchenorrhyncha: Cercopoidea) occurring in Australia has revealed closer links between the Australian fauna and those of the Pacific region than were previously acknowledged. A key to the Australian genera is provided along with a diagnosis for each genus and a list of described Australian species with notes on each. Taxonomic changes proposed are: Neoaphrophora China synonymised with Anyllis Kirkaldy; Eurycercopis Kirkaldy synonymised with Interocrea Walker; Aphrophora rufiventris Walker and Philagra vittata Metcalf and Horton synonymised with Philagra parva (Donovan). New combinations proposed are: Amarusa australis (Jacobi) (from Eoptyelus ); Anyllis tiegsi (China) (from Neoaphrophora ); Interocrea nigrofasciata (Kirkaldy) (from Eurycercopis ); Interocrea regalis (Lallemand) (from Clovia ); Liorhina loxosema (Hacker) (from Clovia ). To provide a single reference point for the species and, for species described by Hacker (1926) and Jacobi (1928) , to validate apparent holotype intentions by those authors, lectotypes are designated for: Ptyelus homochrous Hacker; Eurycercopis nigrofasciata Kirkaldy; Clovia regalis Lallemand; Clovia loxosema Hacker; Philagra concolor Hacker; Philagra fulvida Hacker; Philagra recurva Jacobi. The probable whereabouts of the type specimen of Philagra parva (Donovan) are discussed. The origin of the holotype of Novaphrophara tasmaniae Lallemand is discussed; the Australian record is almost certainly incorrect.     

Phylogenetic relationships among calyptraeid gastropods and their implications for the biogeography of marine speciation

Although calyptraeid gastropods are not well understood taxonomically, in part because their simple plastic shells are the primary taxonomic character, they provide an ideal system to examine questions about evolution in the marine environment. I conducted a phylogenetic analysis of calyptraeid gastropods using DNA sequence data from mitochondrial cytochrome oxidase I (COI) and 16S genes and the nuclear 28S gene. The resultant phylogeny was used to examine the biogeographic patterns of speciation in the Calyptraeidae. Parsimony and Bayesian analyses of the combined data sets for 94 calyptraeid operational taxonomic units and 24 outgroups produced well-resolved phylogenies. Both approaches resulted in identical sister-species relationships, and the few differences in deeper topology did not affect biogeographic inferences. The geographic distribution of the species included here demonstrate numerous dispersal events both between the Pacific and Atlantic oceans and across the equator. When parsimony is used to reconstruct the movement from the Pacific to the Atlantic oceans on the phylogeny, there are 12 transitions between oceans, primarily from the Pacific to the Atlantic. When the latitude is coded as north versus south of the equator, the most-parsimonious reconstruction gives the origin of calyptraeids in the north followed by 15 dispersal events to regions south of the equator and no returns to the north. Many clades of the most closely related species are either sympatric or occur along a single coastline. Closely related species can, however, occur in such divergent regions as Southern California and South Africa. There is little evidence for sister-species pairs or larger clades having been split by the Isthmus of Panama or the Benguela upwelling, but the East Pacific Barrier appears to separate the most basal taxa from the rest of the family.     

Climate impacts on transocean dispersal and habitat in gray whales from the Pleistocene to 2100

Arctic animals face dramatic habitat alteration due to ongoing climate change. Understanding how such species have responded to past glacial cycles can help us forecast their response to today's changing climate. Gray whales are among those marine species likely to be strongly affected by Arctic climate change, but a thorough analysis of past climate impacts on this species has been complicated by lack of information about an extinct population in the Atlantic. While little is known about the history of Atlantic gray whales or their relationship to the extant Pacific population, the extirpation of the Atlantic population during historical times has been attributed to whaling. We used a combination of ancient and modern DNA, radiocarbon dating and predictive habitat modelling to better understand the distribution of gray whales during the Pleistocene and Holocene. Our results reveal that dispersal between the Pacific and Atlantic was climate dependent and occurred both during the Pleistocene prior to the last glacial period and the early Holocene immediately following the opening of the Bering Strait. Genetic diversity in the Atlantic declined over an extended interval that predates the period of intensive commercial whaling, indicating this decline may have been precipitated by Holocene climate or other ecological causes. These first genetic data for Atlantic gray whales, particularly when combined with predictive habitat models for the year 2100, suggest that two recent sightings of gray whales in the Atlantic may represent the beginning of the expansion of this species' habitat beyond its currently realized range.     

Speciation and diversity on tropical rocky shores: a global phylogeny of snails of the genus Echinolittorina

A phylogenetic approach to the origin and maintenance of species diversity ideally requires the sampling of all species within a clade, confirmation that they are evolutionarily distinct entities, and knowledge of their geographical distributions. In the marine tropics such studies have mostly been of fish and reef-associated organisms, usually with high dispersal. In contrast, snails of the genus Echinolittorina (Littorinidae) are restricted to rocky shores, have a four-week pelagic development (and recorded dispersal up to 1400 km), and show different evolutionary patterns. We present a complete molecular phylogeny of Echinolittorina, derived from Bayesian analysis of sequences from nuclear 28S rRNA and mitochondrial 12S rRNA and COI genes (nodal support indicated by posterior probabilities, maximum likelihood, and neighbor-joining bootstrap). This consists of 59 evolutionarily significant units (ESUs), including all 50 known taxonomic species. The 26 ESUs found in the Indo-West Pacific region form a single clade, whereas the eastern Pacific and Atlantic species are basal. The earliest fossil occurred in the Tethys during the middle Eocene and we suggest that the Indo-West Pacific clade has been isolated since closure of the Tethyan seaway in the early Miocene. The geographical distributions of all species (based on more than 3700 locality records) appear to be circumscribed by barriers of low temperature, unsuitable sedimentary habitat, stretches of open water exceeding about 1400 km, and differences in oceanographic conditions on the continuum between oceanic and continental. The geographical ranges of sister species show little or no overlap, indicating that the speciation mode is predominantly allopatric. Furthermore, range expansion following speciation appears to have been limited, because a high degree of allopatry is maintained through three to five branching points of the phylogeny. This may be explained by infrequent long-distance colonization, habitat specialization on the oceanic/continental gradient, and perhaps by interspecific competition. In the eastern Pacific plus Atlantic we identify five cases of divergence on either side of the Isthmus of Panama, but our estimates of their ages pre-date the emergence of the Isthmus. There are three examples of sister relationships between species in the western Atlantic and eastern Atlantic, all resulting from dispersal to the east. Within the Indo-West Pacific, we find no geographical pattern of speciation events; narrowly endemic species of recent origin are present in both peripheral and central parts of the region. Evidence from estimated divergence times of sister species, and from a plot of the number of lineages over time, suggest that there has been no acceleration of diversification during the glacio-eustatic cycles of the Plio-Pleistocene. In comparison with reefal organisms, species of Echinolittorina on rocky shores may be less susceptible to extinction or isolation during sea-level fluctuations. The species richness of Echinolittorina in the classical biogeographic provinces conforms to the common pattern of highest diversity (11 species) in the central "East Indies Triangle" of the Indo-West Pacific, with a subsidiary focus in the eastern Pacific and western Atlantic, and lowest diversity in the eastern Atlantic. The diversity focus in the East Indies Triangle is produced by a mosaic of restricted allopatric species and overlap of a few widespread ones, and is the result of habitat specialization rather than historical vicariance. This study emphasizes the plurality of biogeographic histories and speciation patterns in the marine tropics.     

A biological consequence of reducing Arctic ice cover: arrival of the Pacific diatom Neodenticula seminae in the North Atlantic for the first time in 800 000 years

The Continuous Plankton Recorder survey has monitored plankton in the Northwest Atlantic at monthly intervals since 1962, with an interegnum between 1978 and 1990. In May 1999, large numbers of the Pacific diatom Neodenticula seminae were found in Continuous Plankton Recorder (CPR) samples in the Labrador Sea as the first record in the North Atlantic for more than 800 000 years. The event coincided with modifications in Arctic hydrography and circulation, increased flows of Pacific water into the Northwest Atlantic and in the previous year the exceptional occurrence of extensive ice‐free water to the North of Canada. These observations indicate that N. seminae was carried in a pulse of Pacific water in 1998/early 1999 via the Canadian Arctic Archipelago and/or Fram Strait. The species occurred previously in the North Atlantic during the Pleistocene from∼1.2 to∼0.8 Ma as recorded in deep sea sediment cores. The reappearance of N. seminae in the North Atlantic is an indicator of the scale and speed of changes that are taking place in the Arctic and North Atlantic oceans as a consequence of regional climate warming. Because of the unusual nature of the event it appears that a threshold has been passed, marking a change in the circulation between the North Pacific and North Atlantic Oceans via the Arctic. Trans‐Arctic migrations from the Pacific into the Atlantic are likely to occur increasingly over the next 100 years as Arctic ice continues to melt affecting Atlantic biodiversity and the biological pump with consequent feedbacks to the carbon cycle.     

Genetic variation and taxonomic analysis of the subgenus Profundulus

The current taxonomy within the subgenus Profundulus was reviewed and at least five different species were recognized on the basis of unique genetic characters. Two of them are considered to be new species not yet described: one is known only from a single spring in the Tehuantepec basin (Mexico); the second extends mainly through springs in the Mixteca region of Mexico. The maximum Nei distances were found between P. oaxacae and the rest of the species belonging to this subgenus. Compared with the other Profundulus species, the new species from Mixteca also had high Nei values, which suggest separation of these species probably during the Miocene period. Therefore, the previously postulated old Central American origin of Profundulus is supported by our data. The mountain uplift that gave rise to the current division of Pacific and Atlantic rivers may be the reason for the current distribution pattern of the subgenus Profundulus . The sporadic presence of this subgenus in the headwaters of some Atlantic rivers has been interpreted as the result of fluvial captures during the Pleistocene period.     

Epithelial moulds on the shells of the early Palaeozoic brachiopod Lingulella

A fine hexagonal network of microscopic ridges has been discovered on the internal shell surface of the cosmopolitan Lower Palaeozoic inarticulate genus Lingulella. The micro-ornamentation has been recognised on all well-preserved specimens examined, from Cambrian and Ordovician successions in Ireland, North America, Gt. Britain, Spitzbergen, and China. Examination of the mantle of the related Recent genus Lingula revealed that the outer epithelial cells are arranged in a hexagonal close-packed pattern comparable in size and form to the micro-ornamentation in the fossil shells. This fact, along with the discovery of a polygonal pattern on some organic layers in the Lingula shell, suggests that the micro-ornamentation in fossil Lingulella is the mould of the outer epithelium responsible for shell secretion. No trace of epithelial moulds has yet been found in specimens of Lingula from younger Palaeozoic successions. This difference may prove to be a useful diagnostic feature in distinguishing linguloid inarticulates from one another. Epithelial moulds , Lingulella, Palaeoglossa, Lingula, Cambrian, Ordovician, Recent.