Terebratulid Brachiopods Research Articles

Microbilobata, a new genus of earliest terebratulid brachiopod from the lower Silurian of Northwestern Canada: Implications for the origin of higher taxa

Microbilobata avalanchensis n. gen. and n. sp. from the Lower Silurian (upper Wenlock) carbonate rocks of the lower Delorme Group in the Avalanche Lake area, northwestern Canada, is described here as the earliest known terebratulid brachiopod. These small shells (less than 2 mm long) are subtriangular, anteriorly emarginate, possibly punctate, with both valves being sulcate at their anterior halves, the ventral sulcus bearing one prominent plica, and the dorsal sulcus marked by two plicae. Internally, M. avalanchensis has a centronelliform loop extending for about three fifths of the total shell length. The shells are silicified in carbonate rocks of mid to outer shelf origin. M. avalanchensis is relatively rare, with about 40 specimens so far found from samples collected at 58–60 m above the base of section AV5 in the Avalanche Lake area. Its presence in rocks of Wenlock age extends the earliest known terebratulids back about 16 million years from the oldest previously recorded terebratulids (earliest De...

Epibiota and attachment substrata of deep-water brachiopods from Antarctica and New Zealand

Prevalence (proportion of host organisms covered) and cover of encrusting epibiota were investigated for four Antarctic and two New Zealand species of deep-sea brachiopods. All epibiota was identified to the lowest possible taxonomic level, such that prevalence and dominance of each taxon could be assessed on different brachiopod species. Punctae had no detectable influence on fouling, whereas valve architecture and ornamentation were probably a major influence. Prevalence and percent cover of epibiota were found to decrease with depth (from 50-600 m) in the Antarctic terebratulidLiothyrella uva. A maximum of 5 % epibiotic cover was recorded on the punctate terebratulids from beyond 160 m (Liothyrella uva,Magellania fragilisandMagellania joubinifrom Antarctica andNeothyris lenticularisfrom New Zealand). Epibiotic cover significantly increased with valve area to over 40 % in the Antarctic inarticulateNeocrania lecointeiand the New Zealand impunctate rynchonellidNotosaria nigricans. Bryozoans, foraminiferans and polychaetes were the most abundant colonizers, but there were also representatives present from seven other phyla. The epibiotic community structure of the terebratulidsLiothyrella uva,Magellania joubiniandNeothyris lenticularis, and the inarticulateNeocrania lecointeiwere broadly similar, suggesting a cosmopolitan nature to deep-sea brachiopod epibiota. The community onMagellania fragiliswas notably different, in being almost entirely dominated by foraminiferans, but the reasons for this are unknown. Analyses of attachment substrata for the Antarctic terebratulid brachiopods indicated erect bryozoans were most commonly used, but that sponges, rocks and even echinoid spines were used. The substratum used by the majority of the New Zealand specimens was unknown, but this is possibly becauseN. lenticularishas been described as degenerating its attachment and becoming free-living with age.

Middle Eocene terebratulide brachiopods from the Bateque Formation, Baja California Sur, Mexico

Two species of terebratulide brachiopods are described from the upper part of the Bateque Formation (middle Eocene) on the Pacific coast of Baja California Sur, Mexico,Terebratulinacf.Terebratulina louisianaeStenzel, 1940, andTerebratalia batequian. sp.Terebratalia batequian. sp. is the earliest confirmed record of the genusTerebrataliaBeecher, 1893, which has been an important component of Pacific brachiopod faunas through to the present day. The occurrence ofTerebratulinacf.Terebratulina louisianaeStenzel is one of the earliest records of the genus from the west coast of North America. These brachiopods, like other elements of the Bateque invertebrate fauna, may record Eocene migration from the Atlantic to Pacific Ocean via the Central American seaway.

Upper Triassic Invertebrates from the Antimonio Formation, Sonora, Mexico

A diverse Upper Triassic tropical marine fauna from northwestern Sonora, Mexico, includes 31 taxa of tropical invertebrates including scleractinian corals, spongiomorphs, disjectoporoids, “hydrozoans,” thalamid and nonthalamid sponges, spiriferid and terebratulid brachiopods, gastropods, bivalves, coleoids, and anomuran microcoprolites. They occur within the late Karnian to Norian part of the Antimonio Formation (Antimonio terrane), which is juxtaposed against a fragmented portion of the North American craton. Most of the fauna is also known from the Tethys region. Sixteen Sonoran taxa co-occur in the western Tethys and five have never been known outside this region. Four additional taxa (one identified only at genus level) are geographically widespread. Some taxa occur in displaced terranes of North America, especially in west-central Nevada (Luning Formation). A weak link exists with the California Eastern Klamath terrane but stronger ties exist with Peru. Among Sonoran sponges,Nevadathalamia polystomawas previously recognized only from the Luning Formation, western Nevada. SpongesCinnabaria expansa, Nevadathalamia cylindrica, and a coral,Astraeomorpha sonorensisn. sp., are also known from Nevada. The coralsDistichomeandra austriaca, Chondrocoenia waltheri, Pamiroseris rectilamellosa, andAlpinophyllia flexuosaco-occur in central Europe. Two new taxa, a spongiomorph hydrozoan,Stromatoporidium lamellatumn. sp., and a disjectoporoid,Pamiropora sonorensisn. sp., have distinct affinities with the Tethys. The geographically widespread North American brachiopod,Spondylospira lewesensis, andPseudorhaetina antimoniensisn. gen. and sp. are among the Sonoran fauna. The Sonoran coleoid (aulacocerid)Dictyoconites(Dictyoconites) cf.D. reticulatumoccurs in the Tethys realm andCalliconitescf.C. drakeiis comparable with a species from the Eastern Klamath terrane.Calliconites millerin. sp. is the first occurrence of the genus outside Sicily. The bivalvesMyophorigonia jaworskii, M. salasi, andPalaeocardita peruvianaare known from Sonora and Peru. Eight gastropod taxa includeGuidoniacf.G. intermediaandG.cf.G. parvula, both previously known from Peru, andEucycloscala subbisertusfrom the western Tethys. The gastropods are unlike those already known from other North American terranes.

Observations on the reproduction and development ofLiothyrella neozelanicaThomson 1918 (Terebratulacea, Articulata, Brachiopoda)

Mature individuals of the terebratulid brachiopod Liothyrella neozelanica Thomson, collected from Doubtful Sound on 25–26 February 1990 at Campbell Kingdom, spawned in the laboratory. The females brooded their opaque, white zygotes, embryos and larvae in the space bounded by the brachial membrane and its associated cirri in the apical region of the median spiral arm of the plectolophe. The coeloblastula gastrulated by invagination. The circular blastopore gradually elongated during gastrulation. Cilia, which first appeared during the gastrula stage, completely covered the embryo and persisted throughout larval life. The cylindroid gastrula developed into a wedge‐shaped larva, which returned to a cylindroid shape before the mantle fold appeared. Two grooves formed on each side of the mantle fold to constrict the larva into a three‐lobed body without eye spots. An occasional two‐lobed stage intervened whenever the two grooves developed asynchronously. Three‐lobed larvae could be classified by morphological features into early, late and pre‐settlement stages. Large ova developed into large larvae or occasionally into large incomplete larvae. Small ova produced miniature but otherwise normal larvae and some miniature incomplete larvae. Incomplete larvae did not differentiate further, had no pedicle lobe, and soon died. The reproduction and development of this species were discussed.

Ultrastructure of the loop of terebratulide brachiopods

The folded and twisted calcareous ribbon, forming both the ascending and descending lamellae of the loop of Waltonia inconspicua (Sowerby), is a two-layered structure consisting of a wedge of regularly stacked secondary layer fibres that overlie a thin layer of non-fibrous calcite (herein termed brachiotest). On one surface, that facing into the mantle cavity, secondary fibrous mosaic predominates, but smooth, finely banded brachiotest occurs as a narrow marginal lip upon which secondary layer fibres proliferate and progressively overlap. This growing edge of the ribbon is secreted by long, folded epithelial cells with digitate extensions to their apical plasmalemmas, which are distinguishable from the cuboidal epithelium-secreting fibres and their membranous sheaths. The other surface, facing the body cavity and the brachial coelom, consists entirely of roughened brachiotest exhibiting prominent banding that is aligned parallel to the growing loop edge. This surface is overlain by microfilamentar epithelium acting as a holdfast for the connective tissue frame of the lophophore. The other edge of the ribbon consists of truncated sections of both secondary-layer fibres and brachiotest which bear signs of resorption consistent with the degenerated state of the associated epithelium. Growth of the Waltonia loop is controlled by these localized processes of secretion and resorption of the fibrous and brachiotest layers and is typical of all terebratulides so far studied. The brachiotest is not homologous with the non-fibrous primary shell secreted at the valve margin. □Brachiopoda, Articulata, Terebratulida, ultrastructure, lophophore, loop.

Passive Deterioration of Shelly Material: A Study of the Recent Eastern Pacific Articulate Brachiopod Terebratalia transversa Sowerby

The preservation potential of a brachiopod shell is in part determined by the post-mortem loss in its mechanical resilience to physical destruction. The loss of mechanical resistance, whether due to the decay of the shell's organic matrix or other processes, can be observed using engineering testing technigues. Tests at various post-mortem intervals on evacuated shells of a population of the extant eastern Pacific terebratulid brachiopod from the San Juan Islands, Terebratalia transversa, revealed that a measurable decrease in preservation potential had occurred. This decrease is demonstrated by the loss of structural integrity of both the hinging mechanism in articulated specimens, and of the shell walls of the individual valves

Calloria, a replacement name for the Recent brachiopod genusWaltoniafrom New Zealand

The new generic name Calloria is proposed as a replacement for Waltonia Davidson, 1850, the type species of which is the common smooth red endemic terebratulide brachiopod of New Zealand seas. Waltonia was based on a juvenile, imperfect specimen of a ribbed brachiopod belonging to an existing genus, and was abandoned by Davidson in 1861. The complex later nomenclatural history of Waltonia and Magasella Dall is described in detail. A type is selected for Terebratula inconspicua Sowerby, 1846, the type species of Calloria n. gen.

An intracrystalline chromoprotein from red brachiopod shells: Implications for the process of biomineralization

1. 1. The red colour of some terebratulid brachiopod shells is caused by a small chromoprotein that occurs within the calcium carbonate matrix of the shell. 2. 2. This carotenoid-protein complex was isolated from within the calcite shell of three different brachiopod genera and may therefore be involved in the process of biomineralization. 3. 3. The apparent molecular weight of this protein, as judged by SDS-PAGE, is 6.5 kDa. 4. 4. The partial N- terminal amino acid sequence of the protein is virtually identical in three different brachipod genera, indicating homology. 5. 5. Two carotenoids are present in Terebratella sanguinea: canthaxanthin and the tentatively identified monoacetylinic analogue of astaxanthin.

Patterns of loop development in post-Paleozoic terebratulid brachiopods and their evolutionary significance

Studies of loop ultrastructure reveal much about both the processes and patterns of loop growth in brachiopods. Such studies also provide useful insight into evolutionary relationships between various main loop-bearing brachiopod taxa. At least five different loop types, two short-looped and three long-looped, are recognisable in Cenozoic Terebratulida.Loop development in short-looped forms is relatively unspectacular and of limited value for evolutionary studies. It consists of the growth of either an undulating transverse ribbon extending between two short crura (in the Family Terebratulidae) or, where crural processes are united (as in most Cancellothyrididae), a ring. In all short-looped forms the loop is derived from, and hence supported solely by, the crura throughout ontogeny.The early stages of loop development in the great majority of post-Paleozoic long-looped brachiopods are similar. A septal pillar, located centrally in the dorsal valve floor, appears generally very early in ontogeny. Rudimentary descending branch elements are generated both from the crura and the flanks of the septal pillar. Rudimentary ascending elements develop at either the ventral or posteroventral edge of the septal pillar and consist firstly of an inverted or steeply inclined and continuously expanding cone or hood which, through resorption of its posteriorly located apex, becomes transformed into a ring. Further growth sees firstly the fusion of the anterior extremeties of adjacent ascending and descending loop elements followed by their progressive anterolateral separation from the septal pillar.Contrasting modes of growth characterise the later stages of loop development in the three main groups of long-looped brachiopods. In Dallinidae, ascending and descending elements detach from the septum to give rise to a long, reflected loop supported only by the crura. In Terebratellidae, a pair of narrow, laterally directed but anteriorly migrating struts anchor the the descending branches to the median septum. These struts, in structural continuity with the median septum, are built up entirely from secondary layer fibres. In Laqueidae, in addition to a pair of septal struts, a pair of anterolaterally migrating vertical bands spanning the gap between adjacent ascending and descending branches provide further support. Unlike the septal struts but like the remaining ascending and descending loop elements, the vertical bands are constructed from both primary and secondary shell layers. Growth line discordancies at the junctions between the vertical bands and contiguous ascending and descending elements indicate the structural integrity of the vertical bands.

Growth increments in the shell of the living brachiopod Terebratalia transversa

Scanning electron micrographs revealed growth increments in the primary shell layer of the extant terebratulid brachiopod Terebratalia transversa collected from Anacortes, Washington, USA, during the summers of 1982–1984. The increments extend into the secondary shell layer, but only as poorly-defined continuations. Growth increments narrow and widen cyclically, producing patterns similar to tidally-induced, fortnightly growth patterns in bivalve molluscs. “Asymmetric” increments or “doublets” that consist of paired wide and narrow bands present additional evidence that the growth pattern is produced by the interference of tidal (24 h 50 min) and solar (24 h) daily environmental influences on growth, as is the case in bivalves. Growth increments are relatively well-defined in specimens from tidal habitats and are poorly-defined in subtidal specimens. Specimens grown in laboratory aquaria and subjected to simulated tidal emersions and submersions had well-defined increments, whereas those that were continuously submerged in aquaria had poorly-defined increments, paralleling the distinctness in growth increments produced at various depths in the natural habitat. Production of growth increments in T. transversa may be related to valve movement and changes in mantle-cavity pH. When the valves are closed, pH drops and, when they are open, pH rises. Highperformance liquid chromatography (HPLC) of mantle tissue and fluid failed to detect any single organic acid that could have been responsible for the pH changes, confirming that intermediate metabolism in T. transversa is very low compared to that of bivalve molluscs. Calculations indicate that cycles in intermediate metabolism may nevertheless be responsible for cycles in growth-increment production and shell dissolution.

Lithiotis (Bivalvia) bioherms in the Lower Jurassic of east-central Oregon, U.S.A

The epifaunal, rudist-like bivalve Lithiotis formed extensive bioherms during the Pliensbachian and Toarcian ages of the Early Jurassic. The best developed bioherms in North America occur in the Pliensbachian Robertson Formation of east-central Oregon, a unit deposited in a shallow sea transgressing across the Suplee shelf. A typical bioherm consists of three biofacies that coexisted laterally and replaced each other vertically. The reef flank assemblage is the most diverse consisting of Nerinea gastropods, terebratulid brachiopods and Lithiotis debris in a calcarenite or calcilutite matrix. The death assemblage consists of tightly packed, current-aligned Lithiotis valves with gastropods and brachiopods much reduced in numbers. The core of the reef is built almost exclusively of in situ Lithiotis forming a bafflestone with a calcilutite matrix. Lithiotis inhabited a stressful environment inimical to most invertebrates since diversity is very low and there is no evidence of bioerosion. During the Pliensbachian, Lithiotis formed an endemic centre encompassing western North America and the Tethyan Ocean, linked through central America and the central Atlantic by the Hispanic Corridor. By the close of the Pliensbachian it had disappeared from North America but in the Toarcian made its first appearance in South America. By the end of the Toarcian, Lithiotis was extinct.

Late Mississippian bryozoan/microbial build‐ups on a drowned karst terrain: Port au Port Peninsula, western Newfoundland

ABSTRACTBryozoan and microbial carbonate build‐ups occur within the Late Mississippian (mid‐Viséan) Codroy Group on the Port au Port Peninsula, western Newfoundland. Build‐ups formed only adjacent to a rocky, cliffed, shoreline filling narrow submerged palaeovalleys of a well‐developed Late Devonian‐Early Mississippian karst terrain. The nearshore setting was a stressed environment as indicated by (1) the absence of normal marine biota, such as corals, echinoderms, and calcareous algae, (2) high numbers and low species diversity of dominant taxa (bryozoans, brachiopods, and microbial communities), and (3) abundant plant‐bearing siliciclastics deposited by the episodic influx of fresh‐water from adjacent uplands. Build‐up development was terminated by Meramec time, due to falling sea‐level and seaward progradation of terrestrial sediments.Preserved structural and constructional fabrics within the build‐ups include (1) thickets of bryozoans and microbial microthrombolites, structurally enhanced by probable marine Mg‐calcite and aragonite cements, (2) multigeneration internal sediment, and (3) small colonies of serpulid worms and terebratulid brachiopods. Submarine cementation within the build‐ups appears to have been abundant during arrested sedimentation, whereas intermound sediments (carbonates and siliciclastics) were lithified only during burial diagenesis. Shallow‐burial fracturing, stylolitization, sulphide and sulphate mineralization, and precipitation of phreatic, iron‐poor, calcite cement occurred during burial diagenesis.Codroy build‐ups are distinct from the more common Mississippian mud mounds. Their internal characteristics and the geologic setting are more like other Late Palaeozoic and Holocene bryozoan‐rich build‐ups.

Secretion and ultrastructure of the periostracum of some terebratulide brachiopods

A survey of the periostracum of representative species of living terebratulide brachiopods reveals that it originates within a slot separating the lobate and vesicular cells of the outer mantle lobe and that three fundamentally different types are synthesized beneath a mucopolysaccharide film exuded by the lobate cells. The simplest type, which is found among the Terebratulacea, consist of a uniformly textured, electron-dense layer, either splaying externally at irregular intervals into acutely disposed subsidiary sheets up to 4 μm long as in Terebratulina , or bearing externally scattered secretion droplets and rare vesicles as in Liothyrella . This simple type of periostracum is a correlative of an undifferentiated basal layer which underlies the periostracal succession of all known terebratellaceans, not only in its structure, but also in its secretion by the vesicular cell region of the outer mantle lobe. The basal layer of terebratellaceans, however, supports a complex superstructure. In Waltonia and other terebratellids as well as dallinids, kraussinids, laqueids and possibly platitiids, the superstructure is an elaborate proteinous succession composed of vesicles and secretion droplets amalgamated by accretionary growth and fashioned by partial resorption into a labyrinthine structure covered by fibrillar proteinous rods arranged in undulating interconnected rows. In the megathyridid Gwynia , the superstructure consists of proteinous sheets secreted as a series of isoclinal folds normal to the basal layer. Both types of superstructure as well as the secretion droplets and vesicles of Liothyrella are exuded mainly by distal lobate cells forming the outer boundary of the periostracal slot. This difference in origin between the basal layer and the superstructure precludes consideration of periostraca as chronologically stratified successions. Concordance of the various types with the phylogenetic history of the Order based mainly on the evolution of the lophophore supports, suggests that the simplest periostracum is the most primitive type and that it may have been widespread among Palaeozoic brachiopods.

The delthyrial covers of some living brachiopods

Ultrastructural studies of the epithelium associated with the delthyrium and its covers of living rhynchonellide and terebratulide brachiopods show that it is sharply differentiated into two types. The microvillous pedicle epithelium exudes a cuticle bounded by a triple-unit membrane and composed of mucopolysaccharide and chitin; the normally developed outer epithelium secretes periostracum and carbonate. At the junction between the two types which coincides with the delthyrial and notothyrial openings of the young shell, a proteinous membrane or layer is secreted and acts as a bonding sheet between the cuticle and shell. Expansion of the circumference of the junction occurs only at its intersections with a pair of fused mantle lobes responsible for the growth of the cardinal margins. As expansion takes place the junction migrates into the delthyrial cavity leaving behind realigned secondary fibres which are normally coated with a thin carbonate film as well as a cuticular fold; this zone constitutes the pedicle collar. The ventral outer mantle lobes also grow dorso-medianly from their intersection with the pedicle‒outer epithelial junction and secrete a pair of tetrahedral structures, the deltidial plates. Each plate is bounded by an outer surface of primary shell, an inner surface of pedicle collar and an oblique anterior surface of secondary fibres. The deltidial plates can extend medianly only because they grow dorsally of the umbo of the brachial valve. Further growth leads to a median conjunction of deltidial plates and, in some species, to a median fusion of the paired ventral lobes to form a common secretory unit exuding both periostracum and carbonate shell as a continuous structure (symphytium) across the delthyrium. Transverse sections near the posterior margin of the symphytium will always show this origin by fusion of ventral mantle lobes.

Correlative Oligocene Unconformities in Southern Australasia

AN extensive Oligocene unconformity is widespread in shallow marine sequences throughout southern Australia and New Zealand. In southern New Zealand, this surface, a para-conformity1, abruptly truncates a late Cretaceous to Early Oligocene transgressive shelf sequence. The paraconformity is widely recognizable2,3, generally being marked by a veneer (1 to 10 m) of greensand resting in sharp, usually bored, contact with underlying mudstones and marls of late Eocene to early Oligocene. The surface is often phosphatized, locally carries manganese coatings and is sometimes associated with a characteristic hard bottom faunal assemblage. Abraded bioclastic detritus, phosphatic nodules and glauconite pellets (of several discrete types) are widespread within the overlying greensand, but terrigenous sediment is uncommon. A further faunal community, characterized by the mollusc Lentipecten, the terebratulide brachiopod Waipara and relatively abundant vertebrate remains (cetacean and spheniscoformid bone), is characteristic of sediments from just above the paraconformity. Middle to upper Oligocene strata are generally either absent, or represented by the greensand or overlying intensely current-bedded bioclastic limestones4. We believe that the paraconformity can be recognized in shallow marine sequences throughout South Island, New Zealand; only in areas of terrestrial sedimentation (for example, Central Otago) and possibly deep marine sedimentation (for example, Waiau Basin) does the surface appear to be absent. Sediments overlying the paraconformity record regression from open shelf limestones and sandstones (early Miocene) through shallow marine muds and sands to coal measures and thick terrestrial roundstone conglomerates3,5, this upward coarsening sequence reflects the development of late Cainozoic Kaikoura orogenesis in the New Zealand region.