Monophyly of brachiopods and phoronids: reconciliation of molecular evidence with Linnaean classification (the subphylum Phoroniformea nov.)

Molecular phylogenetic analyses of aligned 18S rDNA gene sequences from articulate and inarticulate brachiopods representing all major extant lineages, an enhanced set of phoronids and several unrelated protostome taxa, confirm previous indications that in such data, brachiopod and phoronids form a well-supported clade that (on previous evidence) is unambiguously affiliated with protostomes rather than deuterostomes. Within the brachiopod-phoronid clade, an association between phoronids and inarticulate brachiopods is moderately well supported, whilst a close relationship between phoronids and craniid inarticulates is weakly indicated. Brachiopod-phoronid monophyly is reconciled with the most recent Linnaean classification of brachiopods by abolition of the phylum Phoronida and rediagnosis of the phylum Brachiopoda to include tubiculous, shell-less forms. Recognition that brachiopods and phoronids are close genealogical allies of protostome phyla such as molluscs and annelids, but are much more distantly related to deuterostome phyla such as echinoderms and chordates, implies either (or both) that the morphology and ontogeny of blastopore, mesoderm and coelom formation have been widely misreported or misinterpreted, or that these characters have been subject to extensive homoplasy. This inference, if true, undermines virtually all morphology-based reconstructions of phylogeny made during the past century or more.     

Molecular phylogeny of brachiopods and phoronids based on nuclear-encoded small subunit ribosomal RNA gene sequences

Brachiopod and phoronid phylogeny is inferred from SSU rDNA sequences of 28 articulate and nine inarticulate brachiopods, three phoronids, two ectoprocts and various outgroups, using gene trees reconstructed by weighted parsimony, distance and maximum likelihood methods. Of these sequences, 33 from brachiopods, two from phoronids and one each from an ectoproct and a priapulan are newly determined. The brachiopod sequences belong to 31 different genera and thus survey about 10% of extant genus-level diversity. Sequences determined in different laboratories and those from closely related taxa agree well, but evidence is presented suggesting that one published phoronid sequence (GenBank accession UO12648) is a brachiopod-phoronid chimaera, and this sequence is excluded from the analyses. The chiton, Acanthopleura, is identified as the phenetically proximal outgroup; other selected outgroups were chosen to allow comparison with recent, non-molecular analyses of brachiopod phylogeny. The different outgroups and methods of phylogenetic reconstruction lead to similar results, with differences mainly in the resolution of weakly supported ancient and recent nodes, including the divergence of inarticulate brachiopod sub-phyla, the position of the rhynchonellids in relation to long- and short-looped articulate brachiopod clades and the relationships of some articulate brachiopod genera and species. Attention is drawn to the problem presented by nodes that are strongly supported by non-molecular evidence but receive only low bootstrap resampling support. Overall, the gene trees agree with morphology-based brachiopod taxonomy, but novel relationships are tentatively suggested for thecideidine and megathyrid brachiopods. Articulate brachiopods are found to be monophyletic in all reconstructions, but monophyly of inarticulate brachiopods and the possible inclusion of phoronids in the inarticulate brachiopod clade are less strongly established. Phoronids are clearly excluded from a sister-group relationship with articulate brachiopods, this proposed relationship being due to the rejected, chimaeric sequence (GenBank UO12648). Lineage relative rate tests show no heterogeneity of evolutionary rate among articulate brachiopod sequences, but indicate that inarticulate brachiopod plus phoronid sequences evolve somewhat more slowly. Both brachiopods and phoronids evolve slowly by comparison with other invertebrates. A number of palaeontologically dated times of earliest appearance are used to make upper and lower estimates of the global rate of brachiopod SSU rDNA evolution, and these estimates are used to infer the likely divergence times of other nodes in the gene tree. There is reasonable agreement between most inferred molecular and palaeontological ages. The estimated rates of SSU rDNA sequence evolution suggest that the last common ancestor of brachiopods, chitons and other protostome invertebrates (Lophotrochozoa and Ecdysozoa) lived deep in Precambrian time. Results of this first DNA-based, taxonomically representative analysis of brachiopod phylogeny are in broad agreement with current morphology-based classification and systematics and are largely consistent with the hypothesis that brachiopod shell ontogeny and morphology are a good guide to phylogeny.     

The evolution of the serotonergic nervous system

The pattern of development of the serotonergic nervous system is described from the larvae of ctenophores, platyhelminths, nemerteans, entoprocts, ectoprocts (bryozoans), molluscs, polychaetes, brachiopods, phoronids, echinoderms, enteropneusts and lampreys. The larval brain (apical ganglion) of spiralian protostomes (except nermerteans) generally has three serotonergic neurons and the lateral pair always innervates the ciliary band of the prototroch. In contrast, brachiopods, phoronids, echinoderms and enteropneusts have numerous serotonergic neurons in the apical ganglion from which the ciliary band is innervated. This pattern of development is much like the pattern seen in lamprey embryos and larvae, which leads the author to conclude that the serotonergic raphe system found in vertebrates originated in the larval brain of deuterostome invertebrates. Further, the neural tube of chordates appears to be derived, at least in part, from the ciliary band of deuterostome invertebrate larvae. The evidence shows no sign of a shift in the dorsal ventral orientation within the line leading to the chordates.     

Morphology of gametes of mollusks, echinoderms, and brachiopods in systematics and phylogeny

The morphology of eggs and sperm of echinoderms, mollusks, and brachiopods was studied and compared. The gametes of inarticulate brachiopods (two classes Lingulata and Craniata and two subphyla Linguliformea and Craniaformea) are shown to have significant morphological differences from those of articulate brachiopods (extant class Rhynchonellata, subphylum Rhynchonelliformea). Inarticulate brachiopods have similar sperm morphology to that of primitive brachiopods, bivalves and some polychaetes that have external fertilization. Sperm morphology of articulate brachiopods is similar to that of echinoderms, which are considered to be typical deuterostomate invertebrates. This similarity supports an early deviation of lophophore-bearing animals from Bilateria, before this lineage branched into Protostomia and Deuterostomia. Similar gamete morphology in Lingulata and Craniata supports the view that inarticulate brachiopods should be retained as a supraclass taxon for comparison with other Lophotrochozoa, in particular with phoronids, bryozoans, and mollusks. Based on the new data on the gamete morphology in inarticulate brachiopods, we propose the name Lingulophyles with the type genus Lingula, and for articulate brachiopods Coptothyrophyles with the type genus Coptothyris.     

Rerooting the rDNA gene tree reveals phoronids to be ‘brachiopods without shells’; dangers of wide taxon samples in metazoan phylogenetics (Phoronida; Brachiopoda)

Molecular phylogenetics has resulted in conflicting accounts of the relationship between phoronids and brachiopods. Taxonomically comprehensive analyses of brachiopod and phoronid ribosomal DNA sequences (rDNAs) rooted with short‐branched mollusc sequences uniformly find that phoronids nest within brachiopods as the sister of the three extant inarticulate lineages. Here, this is called the ‘alternate’ topology because it does not match traditional, morphology‐based ideas. Many other analyses of protein‐coding genes and/or rDNAs place phoronids elsewhere, often as the sister group of all brachiopods, better matching ‘traditional’ ideas. However, these analyses generally are based on data from small selections of brachiopods and phoronids, include data from a wide range of other metazoan taxa, and are rooted with distant outgroups. Here, I show that outgroup rooting of brachiopods and phoronid rDNAs is unreliable, and instead find the root position with procedures that are free from all distortions caused by distantly related taxa, i.e. by Bayesian and maximum likelihood relaxed‐clock analyses of a purely ingroup alignment. All such analyses confirm the ‘alternate’ topology: phoronids belong within the Brachiopoda as the sister group of the inarticulates. In addition, nine factors are identified that (singly or in combination) can cause misreporting of the phylogenetic signal in wide taxon‐range analyses of both rDNA and amino acid sequence data. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012.     

苔藓动物18S rRNA基因的分子系统发生初探

本文对我国沿海较为常见的8种唇口目苔藓动物的18SrRNA基因进行了PCR扩增和序列测定。结合已知的其它苔藓动物（包括内肛动物和外肛动物）以及腕足动物和帚虫的相应序列,运用分子系统学方法,研究苔藓动物门的系统发生关系,结果表明,外肛动物和内肛动物构成苔藓动物分子系统树中的二大平行支;本文测定的大室膜孔苔虫与Giribet等测定的膜孔苔虫在系统树中的位置间隔较远。结果也支持外肛动物包含被唇纲和裸唇纲两大类群的形态划分,而关于裸唇纲特别是唇口目内部的系统发生关系。分子数据的分析结果和形态分类之间的分歧有待于进一步研究。     

Trochophora larvae: cell-lineages, ciliary bands and body regions. 2. Other groups and general discussion

The embryology of sipunculans, entoprocts, nemertines, platyhelminths (excluding acoelomorphs), rotifers, ectoprocts, phoronids, brachiopods, echinoderms and enteropneusts is reviewed with special emphasis on cell-lineage and differentiation of ectodermal structures. A group Spiralia comprising the four first-mentioned phyla plus annelids and molluscs seems well defined through the presence of spiral cleavage with early blastomere specification, prototroch with characteristic cell-lineage, cerebral ganglia developing from cells of the first micromere quartet (i.e., the episphere) and a ventral nervous system developing from the hyposphere. The planktotrophic trochophore was probably the larval type of the ancestor of this group. Another group comprising phoronids, brachiopods, echinoderms and enteropneusts appears equally well delimited. It is characterized by radial cleavage with late blastomere specification, possibly by the presence of a neotroch consisting of monociliate cells, by the absence of cerebral ganglia and of a well-defined brain and paired longitudinal nerve cords developing in connection with the blastopore, and by coelomic organization. Its ancestral larval type was probably a dipleurula. Several characters link rotifers with the spiralians, although they do not show the spiral pattern in the cleavage. Ectoprocts are still a problematic group, but some characters indicate spiralian affinities.     

Molecular evidence that phoronids are a subtaxon of brachiopods (Brachiopoda: Phoronata) and that genetic divergence of metazoan phyla began long before the early Cambrian

Concatenated SSU (18S) and partial LSU (28S) sequences (2 kb) from 12 ingroup taxa, comprising 2 phoronids, 2 members of each of the craniid, discinid, and lingulid inarticulate brachiopod lineages, and 4 rhynchonellate, articulate brachiopods (2 rhynchonellides, 1 terebratulide and 1 terebratellide) were aligned with homologous sequences from 6 protostome, deuterostome and sponge outgroups (3964 sites). Regions of potentially ambiguous alignment were removed, and the resulting data (3275 sites, of which 377 were parsimony-informative and 635 variable) were analysed by parsimony, and by maximum and Bayesian likelihood using objectively selected models. There was no base composition heterogeneity. Relative rate tests led to the exclusion (from most analyses) of the more distant outgroups, with retention of the closer pectinid and polyplacophoran (chiton). Parsimony and likelihood bootstrap and Bayesian clade support values were generally high, but only likelihood analyses recovered all brachiopod indicator clades designated a priori. All analyses confirmed the monophyly of (brachiopods+phoronids) and identified phoronids as the sister-group of the three inarticulate brachiopod lineages. Consequently, a revised Linnean classification is proposed in which the subphylum Linguliformea comprises three classes: Lingulata, ‘Phoronata’ (the phoronids), and ‘Craniata’ (the current subphylum Craniiformea). Divergence times of all nodes were estimated by regression from node depths in non-parametrically rate-smoothed and other chronograms, calibrated against palaeontological data, with probable errors not less than 50 My. Only three predicted brachiopod divergence times disagree with palaeontological ages by more than the probable error, and a reasonable explanation exists for at least two. Pruning long-branched ingroups made scant difference to predicted divergence time estimates. The palaeontological age calibration and the existence of Lower Cambrian fossils of both main brachiopod clades together indicate that initial genetic divergence between brachiopod and molluscan (chiton) lineages occurred well before the Lower Cambrian, suggesting that much divergence between metazoan phyla took place in the Proterozoic.

See also Electronic Supplement at: http://www.senckenberg.de/odes/05-11.htm     

The Essential Role of "Minor" Phyla in Molecular Studies of Animal Evolution

SYNOPSIS. Molecular studies have revealed many new hypothesesof metazoan evolution in recent years. Previously, using morphologicalmethods, it was difficult to relate "minor" animal groups representingmicroscopic metazoans to larger, more well known groups suchas arthropods, molluscs, and annelids. Molecular studies suggestthat acanthocephalans evolved from rotifers, that priapulidsshare common ancestry with all other molting animals (Ecdysozoa),and that flatworms, gnathostomulids and rotifers form a sistergroup to the remaining non-molting protostomes (Lophotrochozoa),together forming Spiralia. The lophophorate phyla (phoronids,brachiopods and bryozoans) appear as protostomes, allied withannelids and molluscs rather than with deuterostomes. Thesefindings present a very different view of metazoan evolution,and clearly show that small and simple animals do not necessarilyrepresent ancestral or primitive taxa.     

The Relationships of Entoprocta, Ectoprocta and Phoronida

Comparisons of life-cycles of entoprocts, ectoprocts and phoronidsindicate that the ectoprocts probably have evolved from entoproct-likeancestors, whereas the phoronids are of a quite different type.A review of our knowledge of structure and development of thethree groups lends support to this idea. The Entoprocta andEctoprocta should accordingly be united into the phylum Bryozoa,which is related to the Annelida and Mollusca. The Phoronidaare probably more related to the deuterostomes.     

Phylogenomic analyses of lophophorates (brachiopods, phoronids and bryozoans) confirm the Lophotrochozoa concept

Based on embryological and morphological evidence, Lophophorata was long considered to be the sister or paraphyletic stem group of Deuterostomia. By contrast, molecular data have consistently indicated that the three lophophorate lineages, Ectoprocta, Brachiopoda and Phoronida, are more closely related to trochozoans (annelids, molluscs and related groups) than to deuterostomes. For this reason, the lophophorate groups and Trochozoa were united to Lophotrochozoa. However, the relationships of the lophophorate lineages within Lophotrochozoa are still largely unresolved. Maximum-likelihood and Bayesian analyses were performed based on a dataset comprising 11,445 amino acid positions derived from 79 ribosomal proteins of 39 metazoan taxa including new sequences obtained from a brachiopod and a phoronid. These analyses show that the three lophophorate lineages are affiliated with trochozoan rather than deuterostome phyla. All hypotheses claiming that they are more closely related to Deuterostomia than to Protostomia can be rejected by topology testing. Monophyly of lophophorates was not recovered but that of Bryozoa including Ectoprocta and Entoprocta and monophyly of Brachiozoa including Brachiopoda and Phoronida were strongly supported. Alternative hypotheses that are refuted include (i) Brachiozoa as the sister group of Mollusca, (ii) ectoprocts as sister to all other Lophotrochozoa including Platyzoa, and (iii) ectoprocts as sister or to all other protostomes except chaetognaths.     

Phoronid phylogenetics (Brachiopoda; Phoronata): evidence from morphological cladistics,small and large subunit rDNA sequences,and mitochondrial cox1

A matrix of 24 morphodevelopmental characters and an alignment of small subunit (SSU) and large subunit (LSU) rDNA nuclear and cox1 mitochondrial gene sequences (～4500 sites) were compiled from up to 12 phoronids including most named taxa, but probably constituting only a portion of worldwide diversity. Morphological data were analysed by weighted parsimony; sequence data by maximum and Bayesian likelihood, both with Phoronis ovalis as the local outgroup. Morphological and sequence‐based phylogenies were similar, but not fully congruent. Phoronid rDNAs were almost free from mutational saturation, but cox1 showed strong saturation unless distant outgroups and P. ovalis were omitted, suggesting that many phoronid divergences are old (≥100 Myr). rDNA divergence between named phoronid taxa is generally substantial, but Phoronopsis harmeri (from Vladivostock) and Phoronopsis viridis (from California) are genetically close enough to be conspecific. In another alignment, of 24 taxa, phoronid rDNAs were combined with data from brachiopods and distant (molluscan) outgroups. The relative ages of divergence between phoronids and their brachiopod sister‐groups, of the split between the P. ovalis and non‐ovalis lineages, and of other phoronid splits, were estimated from this alignment with a Bayesian lognormal uncorrelated molecular clock model. Although confidence limits (95% highest probability density) are wide, the results are compatible with an Early Cambrian split between phoronids and brachiopods and with the Upper Devonian latest age suggested for the P. ovalis/non‐ovalis split by the putative phoronid ichnofossil, Talpina. Most other ingroup splits appear to be ～50–200 Myr old. Inclusion of phoronids with brachiopods in the crown clade pan‐Brachiopoda suggests that a distinctive metamorphosis and absence of mineralization are ancestral phoronid apomorphies. Worldwide diversity and possible associations between character‐states and life‐history attributes deserve comprehensive further study.     

The phylogenetic position of entoprocta, ectoprocta, phoronida, and brachiopoda

Ectoprocts, phoronids and brachiopods are often dealt with underthe heading Tentaculata or Lophophorata, sometimes with entoproctsdiscussed in the same chapter, for example in Ruppert and Barnes(1994). The Lophophorata is purported to be held together bythe presence of a "lophophore," a mesosomal tentacle crown withan upstream-collecting ciliary band. However, the mesosomaltentacle crown of pterobranchs has upstream-collecting ciliarybands with monociliate cells, similar to those of phoronidsand brachiopods, although its ontogeny is not well documented.On the contrary, the ectoproct tentacle crown carries a ciliarysieving system with multiciliate cells and the body does notshow archimery, neither during ontogeny nor during budding,so the tentacles cannot be characterized as mesosomal. The entoproctshave tentacles without coelomic canals and with a downstream-collectingciliary system like that of trochophore larvae and adult rotifersand serpulid and sabellid annelids. Planktotrophic phoronidand brachiopod larvae develop tentacles at an early stage, buttheir ciliary system resembles those of echinoderm and enteropneustlarvae. Ectoproct larvae are generally non-feeding, but theplanktotrophic cyphonautes larvae of certain gymnolaemates havea ciliary band resembling that of the adult tentacles. The entoproctshave typical trochophore larvae and many feed with downstream-collectingciliary bands. Phoronids and brachiopods are thus morphologicallyon the deuterostome line, probably as the sister group of the"Neorenalia" or Deuterostomia sensu stricto. The entoproctsare clearly spiralians, although their more precise positionhas not been determined. The position of the ectoprocts is uncertain,but nothing in their morphology indicates deuterostome affinities."Lophophorata" is thus a polyphyletic assemblage and the wordshould disappear from the zoological vocabulary, just as "Vermes"disappeared many years ago.     

Larval and adult brains

Apical organs are a well-known structure in almost all ciliated eumetazoan larvae, although their function is poorly known. A review of the literature indicates that this small ganglion is the "brain" of the early larva, and it seems probable that it represents the brain of the ancestral, holopelagic ancestor of all eumetazoans, the gastraea. This early brain is lost before or at metamorphosis in all groups. Protostomes (excluding phoronids and brachiopods) appear to have brains of dual origin. Their larvae develop a pair of cephalic ganglia at the episphere lateral to the apical organ, and these two ganglia become an important part of the adult brain. The episphere and the cerebral ganglia show Otx expression, whereas Hox gene expression has not been seen in this part of the brain. A ventral nervous system develops around the blastopore, which becomes divided into mouth and anus by fusion of the lateral blastopore lips. The circumblastoporal nerve ring becomes differentiated into a nerve ring around the mouth, becoming part of the adult brain, a pair of ventral nerve cords, in some cases differentiated into a chain of ganglia, and a ring around the anus. This part of the nervous system appears to be homologous with the oral nerve ring of cnidarians. This interpretation is supported by the expression of Hox genes around the cnidarian mouth and in the ventral nervous system of the protostomes. The development of phoronids, brachiopods, echinoderms, and enteropneusts does not lead to the formation of an episphere or to differentiation of cerebral ganglia. In general, a well-defined brain is lacking, and Hox genes are generally not expressed in the larval organs, although this has not been well studied.     

The monophyletic origin of the Brachiopoda

Although it is commonly acepted that the brachiopods descended from phoronid-like ancestors there is dispute over their origin. Traditionally they have been regarded as a monophyletic group, a clade. More recently it has been claimed that brachiopods are polyphyletic and that several of the orders arose independently from separate phoronid-like stocks. The latter point of view implies that brachiopods are not a taxon but merely a grade of organization. Traditional stratophenetic approaches do little to resolve the problem, which may be outside their domain. It is possible, even probable, that the initial radiation involved organisms that lacked mineralized shells. Cladistic analysis of both living forms and Lower Paleozoic taxa strongly supports the contention that brachiopods are monophytetic and closely related to the phoronids. It suggests, however, that the 'inarticulate' Paterinida and Kutorginida are genealogically more closely related to the Articulata than they are to the remaining Inarticulata. □ Brachiopoda, Lophophorata, cladistics, Cambrian.     

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.     

The origin and geometry of radial ribbing patterns in articulate brachiopods

Ackerly, S. C. 1992 07 15: The origin and geometry of radial ribbing patterns in articulate brachiopods.
Geometric models for simple. radial ribbing in articulate brachiopods include (1) ribs radiating isometrically from the shell umbo. (2) divergence of thc ribs from some 'point' within the shell, and (3) reorientation of the ribs at right angles to the shell margin. Analyses of the Orthida, the ancestral taxon of articulate brachiopods, indicate that rib geometries are isometric in Early Cambrian taxa (model 1). but that by the Early Ordovician rib orientations are generally perpendicular to the shell margin (model 3). A combination of functional and morphogenetic Factors explains the ribbing geometries observed in orthide brachiopods.     

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.     

New insights into the larval development of Macandrevia cranium (Müller, 1776) (Brachiopoda: Rhynchonelliformea)

The terebratulid Macandrevia cranium (Müller, 1776) is a representative of articulate brachiopods. However, little is known about its embryology and larval development. In order to obtain reproducible results we used a strict protocol of artificial fertilization under controlled temperature conditions as a basis for our morphological study. Sampling of embryos or developing larvae at frequent intervals led to the most comprehensive collection of preserved developmental stages, ranging from early zygotes to late three-lobed stage larvae. SEM studies of all these stages showed that the development of M. cranium is similar to that of other terebratulid brachiopods. This includes the presence of four bundles of larval setae in three-lobed stage larvae. Our results contradict earlier observations on the development of M. cranium and show that this species exhibits more typical features of articulate brachiopod development than previously thought.     

Larval development of Brachiopod <Emphasis Type="Italic">Coptothyris grayi</Emphasis> (Davidson, 1852) (Brachiopoda,Rhynchonelliformea)

The larval development of the Brachiopod Coptothyris grayi (Davidson, 1852) from the Sea of Japan is described for the first time. Ciliated blastula proved to represent the first free-swimming stage. The blastopore is initially formed as a rounded hole stretching later along the anteroposterior axis. The larva is first divided into two lobes (the apical lobe and the trunk); the mantle lobe is formed later as two lateral folds. Two pairs of seta bundles appear in the late stage larvae. The apical larval lobe in brachiopods is supposed to match the pre-oral lobe and anterior part of the trunk with tentacles in phoronids.