Modern Data on the Innervation of the Lophophore in Lingula anatina (Brachiopoda) Support the Monophyly of the Lophophorates

Evolutionary relationships among members of the Lophophorata remain unclear. Traditionally, the Lophophorata included three phyla: Brachiopoda, Bryozoa or Ectoprocta, and Phoronida. All species in these phyla have a lophophore, which is regarded as a homologous structure of the lophophorates. Because the organization of the nervous system has been traditionally used to establish relationships among groups of animals, information on the organization of the nervous system in the lophophore of phoronids, brachiopods, and bryozoans may help clarify relationships among the lophophorates. In the current study, the innervation of the lophophore of the inarticulate brachiopod Lingula anatina is investigated by modern methods. The lophophore of L. anatina contains three brachial nerves: the main, accessory, and lower brachial nerves. The main brachial nerve is located at the base of the dorsal side of the brachial fold and gives rise to the cross neurite bundles, which pass through the connective tissue and connect the main and accessory brachial nerves. Nerves emanating from the accessory brachial nerve account for most of the tentacle innervation and comprise the frontal, latero-frontal, and latero-abfrontal neurite bundles. The lower brachial nerve gives rise to the abfrontal neurite bundles of the outer tentacles. Comparative analysis revealed the presence of many similar features in the organization of the lophophore nervous system in phoronids, brachiopods, and bryozoans. The main brachial nerve of L. anatina is similar to the dorsal ganglion of phoronids and the cerebral ganglion of bryozoans. The accessory brachial nerve of L. anatina is similar to the minor nerve ring of phoronids and the circumoral nerve ring of bryozoans. All lophophorates have intertentacular neurite bundles, which innervate adjacent tentacles. The presence of similar nerve elements in the lophophore of phoronids, brachiopods, and bryozoans supports the homology of the lophophore and the monophyly of the lophophorates.     

RHYNCHONELLIFORMEAN BRACHIOPODS WITH SOFT-TISSUE PRESERVATION FROM THE EARLY CAMBRIAN CHENGJIANG LAGERSTÄTTE OF SOUTH CHINA

Abstract:  Cosmopolitan kutorginates, the most abundant Early Cambrian rhynchonelliformean brachiopods, became extinct at the end of the Middle Cambrian. Consequently, any information concerning the anatomy of this peculiar lineage of brachiopods has great phylogenetic significance with regard to their extant relatives for analogies with the stem-group clade. Such data have been supplied from fossils of which the soft parts have been preserved in exceptional detail. A new brachiopod, Kutorgina chengjiangensis sp. nov., from the Early Cambrian Chengjiang Lagerstätte of southern China, is described here. It is the first articulated brachiopod species collected from this deposit. The specimens preserve a set of soft-body parts, i.e. lophophore, digestive tract and pedicle, all previously poorly known in almost all Palaeozoic calcareous brachiopod taxa. The lophophore attains an early spirolophe stage, clearly homologous to that in the coeval lingulids. The digestive tract consists of a mouth, oesophagus, swollen stomach, intestine and a terminal anus. The pedicle protruding between the valves is stout and elongate, with annulated lamellae on the surface, and contains a putative cœlomic cavity. K. chengjiangensis displays the characteristics of the stem group of calcareous brachiopods, and illustrates anatomical similarities between Cambrian phosphatic- and calcareous-shelled brachiopods, thus corroborating that the Brachiopoda are a monophyletic group.     

Ultrastructure of the coelom in the brachiopod Lingula anatina

The organization of the coelomic system and the ultrastructure of the coelomic lining are used in phylogenetic analysis to establish the relationships between major taxa. Investigation of the anatomy and ultrastructure of the coelomic system in brachiopods, which are poorly studied, can provide answers to fundamental questions about the evolution of the coelom in coelomic bilaterians. In the current study, the organization of the coelom of the lophophore in the brachiopod Lingula anatina was investigated using semithin sectioning, 3D reconstruction, and transmission electron microscopy. The lophophore of L. anatina contains two main compartments: the preoral coelom and the lophophoral coelom. The lining of the preoral coelom consists of ciliated cells. The lophophoral coelom is subdivided into paired coelomic sacs: the large and small sinuses (= canals). The lining of the lophophoral coelom varies in structure and includes monociliate myoepithelium, alternating epithelial and myoepithelial cells, specialized peritoneum and muscle cells, and podocyte‐like cells. Connections between cells of the coelomic lining are provided by adherens junctions, tight‐like junctions, septate junctions, adhesive junctions, and direct cytoplasmic bridges. The structure of the coelomic lining varies greatly in both of the main stems of the Bilateria, that is, in the Protostomia and Deuterostomia. Because of this great variety, the structure of the coelomic lining cannot by itself be used in phylogenetic analysis. At the same time, the ciliated myoepithelium can be considered as the ancestral type of coelomic lining. The many different kinds of junctions between cells of the coelomic lining may help coordinate the functioning of epithelial cells and muscle cells.     

Structure of the brachiopod lophophore

Data on the development, structure, and functional morphology of the brachiopod lophophore are analyzed. The common origin of the tentacle apparatus in Lophophorata from the postoral ciliary band of the larva is shown. The brachiopod lophophore is based on the brachial axis consisting of the brachial fold running along the row of tentacles. The brachial axis may be attached to the brachial (dorsal) mantle lobe (trocholophe, schizolophe, and ptycholophe lophophores) or extend freely into the mantle cavity to form coiling brachia (spirolophe, zygolophe, and plectolophe lophophores). The circulation of water flows through the mantle cavity in the brachiopods with attached and free lophophores is described. A new hypothesis on the sorting of particles suspended in water during filtration is proposed.     

Functional disposition of the lophophore in living Brachiopoda

Emig, C. C. 1992 07 15: Functional disposition of the lophophore in living Brachiopoda.
The shape and disposition of adult brachiopod lophophores relate to in- and excurrent apertures. to the internal water irrigation system, to shell orientation at substratum and to near-bottom currents. The arrangement of the mantle canals and gonads of different lophophores are induccd by water circulation. The trocholophe (2% of living species) is considered as a plesiomorphic character which represents the basic plan of the lophophore, shared by all Lophophorata. Three different types of schizolophe (10%) are represented in terebratuloids, thecidioids and discinids. The spirolophe (19%), characteristic of rhynchonellides and most inarticulate brachiopods, except the schizolophe Pelagodiscus , has evolved divergently into specific arrangements of the mantle canals and gonads. The zygo-plectolophe (67%) is characteristic of most Terebratulida. The ptycholophe (2%) probably evolved independently in Megathlris and the thecidioids. The mesolophe, known in the fossil chonetdceans, is considered to be a primitive zygo-plectolophe. The median brachiopod sulcus increases the efficiency of the excurrent system and is considered as an evolved character but a homoplasy within the brachiopods. The characteristics of Recent lophophore types have to be taken into account when reconstructing the lophophore in fossil forms. Brachiopoda, Lophophorata, lophophore, water system, orientation, evolution .     

Discovery of ventrally directed spiralia in a Permian spiriferellid brachiopod and implications for its feeding system

Spiralia are lophophore‐supporting, coiled internal structures developed in some extinct brachiopods. In spite of considerable variations in their orientation, the spiralia of most spiriferide and spiriferinide taxa are known to be laterally directed. Recent studies have shown that these brachiopods consistently have a median inhalant and lateral exhalant feeding system. Here, we report a Permian spiriferellid brachiopod fossil (Spiriferella protodraschei) bearing ventrally directed spiralia in its interior. Using the serial sections of the specimen, we have reconstructed the detailed morphology and orientation of the spiralia. Each spiralium in the specimen does not show the apically tapering pattern supposedly universal in all the known types of spiralia: instead it maintains a similar diameter even at its last whorl. The spiralia appear to have directly developed from strong and anteriorly extended crura, consisting of ten whorls in one side and 13 whorls in the other side. As the morphology and orientation of spiralia are immediately associated with the arrangement of spirolophous lophophore within the mantle cavity, the extraordinary orientation and form of the spiralia indicate that this brachiopod likely had developed a considerably modified feeding pattern with respect to most other spirolophous brachiopods. It is postulated that the inhalant/exhalant current circulation of the species (and its descendants) would be considerably different from that of other spiriferide taxa. In particular, the combination of the vertically oriented life posture (free‐lying with thickened ventral apex bottom) and ventrally directed spiralia resembles both fossil atrypide and modern rhynchonellide brachiopods in the orientation of spirolophe, suggesting that some spiriferellid brachiopods may have developed a lateral inhalant/median exhalant feeding current system. A few spiriferide and spiriferinide brachiopod taxa with a weakly transverse but strongly convex ventral valve are noted to exhibit similar modifications in their spiralia, possibly due to the spatial limitation of their mantle cavities.     

Pennsylvanian sea level cycles, nutrient availability and brachiopod paleoecology

As with modern organisms, the spatial and temporal distribution of fossil communities was controlled by both the physical setting in which the organisms lived and by the organisms' physiology and interactions. By studying the sedimentological and geochemical context of fossil communities, it is possible to assess the relative importance of the physical setting and the organisms' physiology. Comparison of Pennsylvanian brachiopod associations with changing sedimentological context (water depth/facies) and nutrient availability indicates that body size is a function of water depth and nutrient availability for most spire-bearing (athyridids and spiriferids) brachiopods but rarely for productid brachiopods. Spire-bearing brachiopods dominate the associations in high-nutrient settings, and productid brachiopods dominate the associations in low-nutrient settings. This difference suggests that physiological differences between brachiopod orders, such as lophophore filtering efficiency, play an important role in controlling their distribution.     

Paleoecology of Auloporida: an example from the Devonian of the Holy Cross Mts., Poland

Substrate specificity of Auloporida (Tabulata) from the Ska?y Fm. (Upper Eifelian-Lower Givetian) of the Holy Cross Mts., Poland, has been recognized. Kyrtatrypa sp., a rare species in the formation (under 5%), was the most often encrusted brachiopod (59% of investigated specimens), while the most often occurring brachiopod, Aulacella eifeliensis (de Verneuil) was nearly not encrusted. The majority of encrusted brachiopods were larger than 20 mm, while smaller brachiopods occur abundantly in the Formation. The substrate specificity has been caused mainly by the ornamentation of the host's shell. The position of corallites along the commissure of the brachiopod shell proves that auloporids often encrusted living hosts. The epizoan probably used water currents produced by brachiopod's lophophore impoverishing the host's food composition, their relationship can therefore be described as scramble competition.     

Rejection Mechanism of Plectolophous Lophophore of Brachiopod <Emphasis Type="Italic">Coptothyris grayi</Emphasis> (Terebratulida,Rhynchonelliformea)

Brachiopoda is a relict group of invertebrate filter feeders that used a tentacle organ, lophophore, for capturing food particles from the water column. Brachiopod extinction apparently occurred due to low productivity of their filtering organ in comparison with more advanced filter-feeders. Investigation of the filtering mechanism of modern brachiopods is essential to understanding their evolutionary fate. This study is devoted to the rejection mechanism of large waste particles from the plectolophous lophophore of brachiopod Coptothyris grayi. The waste particles gather inside of the lophophore on the outer side of the brachial fold. The particles form rows along frontal grooves of outer tentacles and are carried successively to the tentacle tips and move along them, slimed by mucus. One portion of the particles comes off the lophophore and falls down the mantle, while another part is carried to the abfrontal surface of the tentacles. Due to repeated reversals of abfrontal cilia, the particles wavily move along the abfrontal surface of tentacles. Such movement contributes to the secretion of mucus and the formation of particle clots. The clots come off the lophophore and fall down the mantle. The particles are transported along the mantle by cilia to the anterior part of the mantle margin. Here the ciliary reversals that facilitate secretion of mucus and formation of pseudofeces also take place. The latter takes away from the mantle cavity. Thus, only outer tentacles participate in the rejection of large waste particles from the lophophore. Ciliary reversals of the abfrontal surface of tentacles and the mantle are discovered in brachiopods for the first time. This facilitates the additional secretion of mucus and formation of pseudofeces, easing their exit from the mantle cavity. The results contribute to the knowledge of lophophore function and evolution of tentacle organs in Bilateria.     

Cementing strophomenide brachiopods from the Silurian of Gotland (Sweden): Morphology and life habits

Dorsal valves of the cementing strophomenide brachiopods Leptaenoidea silurica Hedström and Liljevallia gotlandica Hedström are described for the first time, and it is shown that both these species could also live ambitopically. The lower Wenlock Scamnomena rugata (Lindström) represents young individuals of the ambitopic variant of Leptaenoidea silurica, and is placed in synonymy, resulting in the valid name for the taxon being Leptaenoidea rugata. The range of this species now spans the whole Wenlock, from the upper Visby Formation to the Klinteberg Formation, and possibly even into the Ludlow. Ambitopic gerontic specimens of L. rugata develop very thick shells, in which the ventral valves have strong curvature, and become deeper not by geniculation but by successive mantle retractions and subsequent re-growth, in a way similar to that of atrypides. This shape was probably an adaptation to “floating” on softer substrates. The thickened gerontic dorsal valves have well-developed lophophoral support, showing the shape of the lophophore, which comprises two branches that curve inwards and then backwards; the lophophore was probably ptycholophous and similar to that in living members of the Thecideidina. Ambitopic specimens of Liljevallia could grow to a much larger size than cementing forms, where the dorsal valves have very large, posterior-facing cardinal process lobes and deeply impressed muscle fields and anterior scars. The presence of a ventral process and long, posteroventrally elongated cardinal process lobes, and the absence of dental plates reveals that Liljevallia was probably an early member of the Douvillinidae and is thus removed from the Leptaenoideidae.     

Body cavities in bryozoans: Functional and phylogenetic implications

Based on morphological evidence, Bryozoa together with Phoronida and Brachiopoda are traditionally combined in the group Lophophorata, although this view has been recently challenged by molecular studies. The core of the concept lies in the presence of the lophophore as well as the nature and arrangement of the body cavities. Bryozoa are the least known in this respect. Here, we focused on the fine structure of the body cavity in 12 bryozoan species: 6 gymnolaemates, 3 stenolaemates and 3 phylactolaemates. In gymnolaemates, the complete epithelial lining of the body cavity is restricted to the lophophore, gut walls, and tentacle sheath. By contrast, the cystid walls are composed only of the ectocyst-producing epidermis without a coelothelium, or an underlying extracellular matrix; only the storage cells and cells of the funicular system contact the epidermis. The nature of the main body cavity in gymnolaemates is unique and may be considered as a secondarily modified coelom. In cyclostomes, both the lophophoral and endosaccal cavities are completely lined with coelothelium, while the exosaccal cavity only has the epidermis along the cystid wall. In gymnolaemates, the lophophore and trunk cavities are divided by an incomplete septum and communicate through two pores. In cyclostomes, the septum has a similar location, but no openings. In Phylactolaemata, the body cavity is undivided: the lophophore and trunk coeloms merge at the bases of the lophophore arms, the epistome cavity joins the trunk, and the forked canal opens into the arm coelom. The coelomic lining of the body is complete except for the epistome, lophophoral arms, and the basal portions of the tentacles, where the cells do not interlock perfectly (this design probably facilitates the ammonia excretion). The observed partitioning of the body cavity in bryozoans differs from that in phoronids and brachiopods, and contradicts the Lophophorata concept.     

A soft-bodied lophophorate from the Silurian of England

Soft-bodied taxa comprise an important component of the extant lophophorate fauna, but convincing fossils of soft-bodied lophophorates are extremely rare. A small fossil lophophorate, attached to a brachiopod dorsal valve, is described from the Silurian (Wenlock Series) Herefordshire Lagerstätte of England. This unmineralized organism was bilaterally symmetrical and comprised a subconical body attached basally to the host and partially enclosed by a broad ‘hood’; the body bore a small, coiled lophophore. Where the hood attached laterally, there is a series of transverse ridges and furrows. The affinities of this organism probably lie with Brachiopoda; the hood is interpreted as the homologue of a dorsal valve/mantle lobe, and the attachment as the homologue of the ventral valve and/or pedicle. The ridges are arranged in a manner that suggests constructional serial repetition, indicating that they are unlikely to represent mantle canals. Extant brachiopods are not serially structured, but morphological and molecular evidence suggests that their ancestors were. The new organism may belong to the brachiopod stem group, and might also represent a significant element of the Palaeozoic lophophorate fauna.     

Discovery of soft parts of a fossil brachiopod in the “Hunsrückschiefer” (Lower Devonian, Germany)

The author recently discovered among 16 discinid brachiopods from the Lower Devonian Hunsrück Slate, by using the X-ray technique, two specimens with mineralized soft parts and pedicle. These are truly unique finds, as previously no bodily preserved pedicle of fossil discinids has been described. Also, they prove that in the Hunsriick Slate soft parts can be pyritized. New shell observations give rise to doubts on the generic assignment ofOrbiculoidea mediorhenana Fuchs 1915. By comparing the anatomy of the related, livingLingula with the extinct discinid in question, a reconstruction of the latter is presented.     

Molecular paleobiological insights into the origin of the Brachiopoda

Most studies of brachiopod evolution have been based on their extensive fossil record, but molecular techniques, due to their independence from the rock record, can offer new insights into the evolution of a clade. Previous molecular phylogenetic hypotheses of brachiopod interrelationships place phoronids within the brachiopods as the sister group to the inarticulates, whereas morphological considerations suggest that Brachiopoda is a monophyletic group. Here, these hypotheses were tested with a molecular phylogenetic analysis of seven nuclear housekeeping genes combined with three ribosomal genes. The combined analysis finds brachiopods to be monophyletic, but with relatively weak support, and the craniid as the sister taxon of all other brachiopods. Phylogenetic-signal dissection suggests that the weak support is caused by the instability of the craniid, which is attracted to the phoronids. Analysis of slowly evolving sites results in a robustly supported monophyletic Brachiopoda and Inarticulata (Linguliformea+Craniiformea), which is regarded as the most likely topology for brachiopod interrelationships. The monophyly of Brachiopoda was further tested with microRNA-based phylogenetics, which are small, noncoding RNA genes whose presence and absence can be used to infer phylogenetic relationships. Two novel microRNAs were characterized supporting the monophyly of brachiopods. Congruence of the traditional molecular phylogenetic analysis, microRNAs, and morphological cladograms suggest that Brachiopoda is monophyletic with Phoronida as its likely sister group. Molecular clock analysis suggests that extant phoronids have a Paleozoic divergence despite their conservative morphology, and that the early brachiopod fossil record is robust, and is not affected by taphonomic factors relating to the late-Precambrian/early-Cambrian phosphogenic event.     

Brachiopods from cryptic coral reef habitats in the northern Red Sea

In contrast to the Palaeozoic to Jurassic fossil record, modern tropical and subtropical shallow-water brachiopods are typically small-sized and mostly restricted to cryptic habitats in coral reefs, but information on microhabitat-composition is scant. At Dahab, northern Red Sea, living brachiopods of the genus Argyrotheca were only detected on massively encrusted coral colonies attached to encrusting foraminifers and coralline red algae. Three samples from autochthonous sediments underneath coral colonies are comparatively rich in the brachiopod genera Megerlia and Argyrotheca, and additionally show low numbers of Novocrania and Thecidellina. Based on a coarse-grain analysis including more than 16,000 components >1 mm, these brachiopod shells co-occur with skeletal components of 11 higher taxa. Decapods, fixosessile foraminifers, molluscs, scleractinians, and coralline red algae clearly dominate the assemblages. Brachiopods in this study always contribute less than 2% to the sediment composition. This confirms previous results that even in brachiopod habitats the contribution of brachiopod shells to the total sediment composition is almost negligible. Our study indicates that brachiopods co-occur with pteriomorph bivalves and other epifauna in the cryptic habitats with limited space for encrusters or epibionts on the undersides of scleractinians and it tentatively supports the hypothesis of brachiopods preferring habitats with low grazing pressure, because shelly components of grazers (polyplacophorans and regular echinoids) are rare in our samples.     

Shell structure,ornamentation and affinity of the problematic early Cambrian brachiopod Heliomedusa orienta

The origin of the Brachiopoda has long been a hotly debated topic, and various models have been proposed following the latest finds of exceptionally preserved material. The lower Cambrian (Stage 3) Heliomedusa orienta from the Chengjiang Konservat-Lagerstätte, eastern Yunnan of South China, is an important example of exceptional preservation. A wide variety of affinities have been proposed for Heliomedusa, but recently it has been suggested to reside within the mickwitziids, which may form a stem group to the Brachiopoda. Detailed studies of exceptionally preserved Heliomedusa have increased our knowledge of the soft-part anatomy of this important early brachiopod, but unfortunately, almost nothing is known about its shell structure. Here, we describe new exceptionally preserved specimens from the Chengjiang biota to better reveal both shell structure and ornamentation. Its reticulate–pustulose ornament and tubular structure are reminiscent of traits seen in other mickwitziid brachiopods. In addition, two types of setae can be observed. Apart from the pyritized marginal mantle setae, some tubules are filled with iron oxides, potentially representing thinner and shorter penetrative setae. Both valves of H. orienta appear to have been less mineralized as compared to Mickwitzia monilifera, and the two species differ in diameter and density of tubules and pustules, and in terms of slightly less projected profile of ventral valve with lower umbo posteromedially placed. Although Heliomedusa clearly is closely related to Mickwitzia, their different preservational modes (compacted poorly mineralized/noncompacted mineralized) make detailed comparison difficult; they are provisionally kept as separate genera pending further studies of better-preserved Chinese material.     

The genus Cryptopora (Brachiopoda) from the Miocene of France and its history and biogeography

The rhynchonellid brachiopod species Cryptopora lovisati(Dreger, 1911) has been identified in the Middle Miocene sandy deposits of France, and its ontogeny and variability are described. This is the first record of the genus Cryptopora Jeffreys from France, although several species of Cryptopora have been already reported from other regions of Europe. Being known since the Lower Palaeocene, Cryptopora is widely distributed in modern seas, ranging from about 60 m down to over 4000 m, and is represented by six extant and about 12 fossil species. C. lovisati has been interpreted as relatively shallow water species living attached to the sediment by a long pedicle. The affinity between C. lovisati and Recent C. curiosa Cooper is discussed.     

Size-frequency and population structure of brachiopods

The living terebratulids, Terabratulina unguicula, Terebratalia transversa, Laqueus vancouverensis, and the rhynchonelid Hemithiris psittacea were studied in the San Juan Islands, Washington, U.S.A. Those results and a review of a the literature lead to the conclusion that most brachiopod populations experience episodic recruitment at intervals which may be irregular. The occurrence of juveniles attached to adults, brooding, and bi- or multimodal size-frequency distributions demonstrate that, contrary to a previously suggested hypothesis, adult brachiopods do not generally exclude juveniles from the same area. The commony observed rarity of small individuals is regarded as a product of local recruitment failure due to patchy distribution of larvae; it does not justify the assumption that brachiopods are unaffected by high post-larval juvenile mortality. However, the frequent rarity of small individuals confirms that this cannot be used as a criterion of transport in assemblages of fossil brachiopods.