Architecture and function of the lophophore in the problematic brachiopod Heliomedusa orienta (Early Cambrian, South China)

The detailed structure of the lophophore is a key diagnostic character in the definition of higher brachiopod taxa. The problematic Heliomedusa orienta Sun and Hou, from the Lower Cambrian Chengjiang Lagerstätte of Yunnan, southwestern China, has a well-preserved lophophore, which is unlike that of any known extant or extinct brachiopods. Based on a comparative study of lophophore disposition in H. orienta and the extant discinid Pelagodiscus atlanticus, the in- and excurrent pattern and shell orientation of H. orienta are described and discussed. Reconstructions of lophophore shape and function are based on numerous specimens and comparison with P. atlanticus. The lophophore is composed of a pair of lophophoral arms that freely arch posteriorly rather than coiling anteriorly as commonly seen in fossil and recent lingulids. The lophophore is attached to the dorsal lobe of the mantle; it has neither calcareous nor chitinous supporting structures, and is disposed symmetrically on either side of the valve midline. The mouth can be inferred to be located at the base of the two brachial tubes, slightly posterior to the anterodorsal projection of the body wall. The lophophoral arms bear laterofrontal tentacles with a double row of cilia along their lateral edge, as in extant lingulid brachiopods. The main brachial axes are also ciliated, which presumably facilitated transport of mucous-bound nutrient particles to the mouth. The unique organization of the lophophore in Heliomedusa is not like any known fossil and living brachiopods. This clearly demonstrates that H. orienta is not a member of any crown group. It is here considered as a member of the brachiopod stem group, which challenges recent interpretations of a close discinid affinity.     

Ultrastructure and immunocytochemistry of the nervous system of the larvae ofLingula anatina andGlottidia sp. (Brachiopoda)

Summary Planktotrophic brachiopod larvae ofGlottidia sp. have been investigated for the occurrence of glyoxylic acid induced fluorescence in catecholamines (CA), and serotonin-like (5-HT) and neuropeptide FMRFamidelike (FMRFamide) immunoreactivity (ir). The location of CA, 5-HT-ir and FMRFamide-ir cells and processes were compared with the location of neurons and nerve processes found by transmission electron microscopy. The apical ganglion contains 5-HT-ir and FMRFamideir cells and processes and CA processes. From the dorsal part of the apical ganglion extend dorsal 5-HT-ir and FMRFamide-ir processes; from the nine pairs of tentacles stage (9. pt) they project to the ventral ganglion. These dorsal lophophore processes follow themusculus lophophoralis and them. brachialis. The 5-HT-ir and some of the FMRFamide-ir processes project along the muscles to the tentacles. From the ventral part of the apical ganglion extend CA, 5-HT-ir and FMRFamide-ir processes which follow the ciliary band of the lophophore and project to the tentacles. An intense band of CA processes was also observed in the lophophore, but the dorsal/ventral location could not be ascertained. The ventral ganglion contains 5-HT-ir and FMRFamide-ir cells which project either caudally on the metasome or rostrally as part of the dorsal lophophore processes. The neuropil of the ventral ganglion contains CA, 5-HT-ir and FMRFamide-ir processes. The nervous system of the planktotrophic brachiopod larvae seems to consist of a ventral lophophore system innervating the ciliary bands and a dorsal lophophore system including the ventral ganglion innervating the body musculature. The latter system develops later in ontogeny and is regarded as a specialization due to the presence of shells and associated musculature. The former system is regarded as homologous with the nervous system of actinotroch larvae (Phoronida) and planktotrophic larvae of the echinoderms.     

Age of the Silurian Wuxiahe Formation in Langao,Northwest China: New conodont data

A recent study of conodonts from the Wuxiahe Formation (lower to middle part) in the Ziyang-Langao region suggested its age of middle Telychian (Llandovery) to lower Sheinwoodian (Wenlock), contradicted by subsequent graptolite studies indicating an age of late Telychian for the same interval. New samples from the Qiaoxi section for conodonts to re-access the age of the Wuxiahe Formation collected in this study show that the lower to middle part of the formation belongs to the Pterospathodus amorphognathoides amorphognathoides Biozone, suggesting the age of late Telychian; thus, the Llandovery–Wenlock boundary in the section is most probably higher than previously estimated, but its precise position is not determined since the identification of the Wenlock graptolite Cyrtograptus cf. lundgreni in the section is to be further confirmed. Based on the conodont faunas recognized in the Qiaoxi and Tianwancun sections, the base of the Wuxiahe Formation in the Ziyang-Langao region is diachronous, i.e., not higher than the upper Telychian Pterospathodus amorphognathoides amorphognathoides Biozone at Qiaoxi, but not lower than the lower Sheinwoodian Kockelella ranuliformis Biozone at the Tianwancun setion.     

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 Devonian age). The small size and simple form of the new species suggest that heterochrony (progenesis) could have played a role in the origin of the Terebratulida. M. avalanchensis serves as a good example of Cope's Rule, indicating that the terebratulids evolved from a very small, unspecialized ancestor. The unusually small size of this taxon also offers one explanation as to why some ancestors or transitional forms of major taxonomic groups are extremely difficult to find in the fossil record.     

ONTOGENETIC NICHE SHIFT IN THE BRACHIOPOD TEREBRATALIA TRANSVERSA: RELATIONSHIP BETWEEN THE LOSS OF ROTATION ABILITY AND ALLOMETRIC GROWTH

Abstract: Many articulated brachiopods experience marked life habit variations during ontogeny because they experience their fluid environment at successively higher Reynolds numbers, and they can change the configuration of their inhalant and exhalant flows as body size increases. We show that the extant brachiopod Terebratalia transversa undergoes a substantial ontogenetic change in reorientation governed by rotation around the pedicle. T. transversa′s reorientation angle (maximum ability to rotate on the pedicle) decreases during ontogeny, from 180 degrees in juveniles to 10–20 degrees in individuals exceeding 5 mm, to complete cessation of rotation in individuals larger than 10 mm. Rotation ability is substantially reduced after T. transversa achieves the adult lophophore configuration and preferred orientation with respect to ambient water currents at a length of 2.5–5 mm. We hypothesize that the rotation angle of T. transversa is determined mainly by the position of ventral and dorsal points of attachment of dorsal pedicle muscles relative to the pedicle. T. transversa shows a close correlation between the ontogenetic change in reorientation angle and ontogeny of morphological traits that are related to points of attachment of dorsal pedicle muscles, although other morphological features can also limit rotation in the adult stage. The major morphological change in cardinalia shape and the observed reduction of rotation affect individuals 2.5–10 mm in length. The position of ventral insertions of dorsal pedicle muscles remains constant, but contraction of dorsal pedicle muscles is functionally handicapped because dorsal insertions shift away from the valve midline, rise above the dorsal valve floor, and become limited by a wide cardinal process early in ontogeny (<5 mm). The rate of increase of cardinal process width and of distance between dorsal pedicle muscle scars substantially decreases in the subadult stage (5–10 mm), and most of the cardinalia shell traits grow nearly isometrically in the adult stage (>10 mm). T. transversa attains smaller shell length in crevices than on exposed substrates. The proportion of small‐sized individuals and population density is lower on exposed substrates than in crevices, indicating higher juvenile mortality on substrates prone to grazing and physical disturbance. The loss of reorientation ability can be a consequence of morphological changes that strengthen substrate attachment and maximize protection against biotic or physical disturbance (1) by minimizing torques around the pedicle axis and/or (2) by shifting energy investments into attachment strength at the expense of the cost involved in reorientation.     

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.     

Quantitative analysis strengthens qualitative assessment: a case study of Devonian brachiopod species

Species recognition attributed to the brachiopod family Atrypidae is evaluated based on qualitative and quantified morphological characters. I identified two brachiopod species—Pseudoatrypa lineata and Pseudoatrypa devoniana—from a rich assemblage of brachiopods recovered from the middle Devonian Genshaw Formation of the Traverse Group. Qualitative examination suggested that the former had fine-medium-sized ribbing, a narrow hinge line, widened anterior, moderately steep mid-anterior fold, domal shaped dorsal valve, and an inflated ventral valve in contrast to the coarse ribbing, widened hinge line, narrow anterior, gentle mid-anterior fold, arched-shape dorsal valve, and flat ventral valve of the latter. The shell outline appears rounded for P. lineata and elongated for P. devoniana. Quantitative assessment of the morphological characters on the dorsal, ventral, anterior, and posterior regions of the valves of the two species using geometric morphometric and statistical analyses suggests that the morphologies of the two species are considerably different (P  $ \ll $  0.01). Thus, qualitative differences between the two atrypid species were further corroborated by quantitative results. This emphasizes the fact that these two species of Pseudoatrypa were indeed different from each other. This study highlights the necessity of incorporating quantified morphological characters to successfully investigate the taxonomic distinctness of fossil invertebrates to the species level.     

First documentation of Llandovery (Silurian) conodont genus Astropentagnathus in China (Langao,Shaanxi Province) and the age of Baiyaya Formation

Age of the Baiyaya Formation in the Ziyang-Langao region of Shaanxi Province remains debatable. Ten samples were taken for conodont biostratigraphical studies from the Tianwancun section. The first discovery of Astropentagnathus in China indicates that the genus has a wider geographical distribution than previously known. Conodont fauna from the Baiyaya Formation suggests that the lower part of the unit corresponds to the Pterospathodus eopennatus Superbiozone, and its upper part to the lower Wenlock (probably mainly to the Kockelella ranuliformis Superbiozone). Diachroneity of the Baiyaya Formation in the region is confirmed by conodont studies from the Tianwancun and Qiaoxi sections. Further studies are required to find out age-variation of the formation more precisely.     

Consistent pattern in the placement of taste sensilla on the labellar lobes of Aedes aegypti

The long sensilla on the labellar lobes of Aedes aegypti were studied using scanning electron microscopy. The surface of the labella is populated by 3 hair-like structures: long sensilla (female 33.5 μm, SD 3.81 n=114; male 32.0 μm, SD 2.69 n=20), short sensilla (female 4.27 μm, SD 0.550 n=15; male 4.52 μm, SD 0.609 n=15), and microtrichia (female 5.00 μm, SD 0.656 n=55; male 5.27 μm, SD 0.376 n=53). This current study is concerned with the long sensilla. The ventral surface of the labella is consistently populated with 10 long sensilla. The dorsal surface is populated by 5 long sensilla. We assigned the base of each sensillum Cartesian co-ordinates describing its relationship to the other sensilla on the ventral and dorsal surfaces of each individual. These Cartesian co-ordinates were pooled and a stringent form of cluster analysis was used to determine if these sensilla could be identified by location on the labella. Sensilla from different individuals are more closely related by position than sensilla on the same individual, suggesting that these sensilla are located in a consistent pattern over the labellar surface. Sensilla were labeled V1–V10 and D1–D5 on the ventral and dorsal surfaces respectively.     

The Development of the Brachiopod Crania (Neocrania) anomala (O. F. Müller)and its Phylogenetic Significance

The freely spawned eggs of Crania go through radial cleavage, embolic gastrulation, and the posteroventral part of the archenteron forms mesoderm through modified enterocoely. The blastopore closes in the posterior end of the larva. The ciliated, lecithotrophic larva has four pairs of coelomic pouches and three pairs of dorsal setal bundles. At metamorphosis, the larva curls ventrally by contraction of a pair of midventral muscles, which are extensions of the first pair of coelomic sacs; the larva attaches by the epithelium just behind the closed blastopore. The brachial valve is secreted by the middle part of the dorsal epithelium and the pedicle valve is secreted by the attachment epithelium. The second pair of coelomic sacs develop small attachment areas at the edge of the dorsal valve and become the lophophore coelom (mesocoel); the third pair of coelomic sacs become the body coelom (metacoel) with the adductor muscles. The posterior position of the closing blastopore is characteristic of deuterostomes. The ventral curving of the settling larva and the formation of both valves from dorsal epithelial areas indicate that the brachiopods have a very short ventral side as opposed to the phoronids. It is concluded that both groups have originated from a creeping ancestor with a straight gut.     

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.     

Seasonal morphophysiological variations in the prostatic complex of the Tarabul’s gerbil (Gerbillus tarabuli)

Gerbillus tarabuli is a nocturnal Saharan rodent which has an annual reproductive cycle characterized by the reproductive activity in spring and a long phase of sexual quiescence in other seasons. We describe the morphology and hormonal regulation of the prostatic complex of this rodent in the two periods, based on anatomical, histological, morphometric, and immunohistochemical analyses. The organisation of this prostatic complex is similar to that reported for Meriones unguiculatus, but different from the prostate of Psammomys obesus, the rat, and the mouse. In addition to the anterior lobes, ventral lobes, and dorsal lobes, the prostatic complex of Gerbillus tarabuli, also includes dorsolateral lobe. Each lobe is composed of a fibro-muscular stroma surrounding a glandular epithelium. Dorsolateral lobes are easily distinguishable by their big volume. The prostate grows and regresses cyclically throughout the year. During the resting season, ventral lobes and anterior lobes showed atrophy, with a significant decrease in both epithelial height and supranuclear area size, and a strong thickening of the fibro-muscular compartment. In dorsal lobes, the epithelial and stromal compartments atrophied and regenerated simultaneously, whereas in dorsolateral lobe the thickness of the epithelium, the supranuclear zone and the stroma increased during resting period. Furthermore, seasonal variations were observed in the distribution and expression of both androgen receptors, and estrogens receptors. Expression patterns of all receptors were lobe-specific. In conclusion, both androgens and estrogens are involved in the homeostasis and regulation of the prostate in Gerbillus tarabuli. Dorsolateral lobe seems to be controlled by a different mechanism than other lobes.     

Do brachiopods show substrate‐related phenotypic variation? A case study from the Burgess Shale

As sessile, benthic filter feeders, brachiopods share an intimate relationship with their chosen substrate. Individuals of Micromitra burgessensis in the Burgess Shale Formation are preserved in life position, attached to a range of hard substrates, including skeletal debris, conspecific brachiopods, sponges and enigmatic tubes. Here we investigate the phenotypic variability of M. burgessensis associated with differing substrate attachments. We apply geometric morphometrics to test for variation by plotting landmarks on the exterior of ventral and dorsal valves of M. burgessensis specimens that are preserved attached to different substrates. Using principal component, canonical variate analyses and anova , we determine that there is some variation in shape related to substrate. Canonical variate analyses, for ventral valves and dorsal valves, indicate that specimens attached to the same substrate are recognizable in shape from specimens attached to other substrate types. The strength of differentiation however, is not robust and combined with our discriminate analysis of separate populations suggests that there is the potential for substrates to exercise only weak control over the morphology of Brachiopoda.     

Nahecaris stuertzi,a phyllocarid crustacean from the Lower Devonian Hunsrück Slate

Restudy ofNahecaris based on new stereo radiographs and re-examination of actual specimens has added the following new information.Nahecaris ranges in shape from long and slender to short and stout, the carapace from deep and rounded to long and narrow. Carapace ornament consists either of thin ridges parallel to the ventral border or inclined rows of irregular lines or cusps, but these characters cannot be consistently correlated with other variables to permit definition of separate species. The carapace is fused to the head, and possibly to the anterior end to the thorax in the area in front of the median dorsal plate. A post-mandibular pyritised band may represent the carapace adductor muscle, which inserts on the mesolateral carinae. The mandible resembles that ofCeratiocaris, while the maxillae are like those of extant leptostracans. The 8 thoracopods are biramous: they have an exopod with finger-like lobes and a stenopodous endopod. Posteriorly the endopods reduce markedly, forming a conical, anteriorly open feeding basket. The predominance of dorso-ventrally flattened specimens, and the wide ventral gape of the carapace valves suggests those valves were spread apart in life.Nahecaris may have pressed itself to the substrate by flexing the carapace rim outward and incurving the ventral region of the carapace. The stout second antennae may have stabilised and propelled the animal over the substrate.Nahecaris is thought to have been benthic and to have fed, likeCeratiocaris, by lifting the substrate into suspension, as well as by picking up large fragments directly with the mandibles.     

Panagrellus ceylonensis n. sp. (Nematoda: Cephalobidae)

Panagrellus ceylonensis n. sp. is described from rubber latex in Ceylon. Its long, slender spicules are curved ventrally with a dorsal deflection at two-thirds of their length. The manubrium is thick and hooked, and the shaft is not widened at the shoulder. The terminal bifurcations are wide, with the dorsal one considerably longer and thicker than the ventral. The main ventral element is continuous with the terminal sheath with the ventral bifurcation arising within it.     

Sunosuchus (Archosauria, Crocodyliformes) from the Toutunhe Formation (Middle Jurassic) of the Southern Junggar Basin (Xinjiang, NW-China)

A new specimen of the widespread Middle Jurassic to Lower Cretaceous Asian gonipholidid crocodilian genus Sunosuchus is described on the basis of a partial skeleton from the Upper Toutunhe Formation (Middle Jurassic, ?Bathonian-Callovian) of Liuhonggou, SW of Urumqi, Xinjiang Uygur Autonomous Region, People’s Republic of China. The specimen is represented by a partial mandible, teeth, vertebrae, limb and girdle bones and osteoderms. It can be distinguished from other nominal species of the genus by a unique combination of characters: slightly heterodontous dentition, strongly sculptured posteroventral part of the mandible, short fenestra mandibularis, convex dorsal surface of the retroarticular process, keeled cervical vertebral centra and ventral osteoderms with a distinctive sculpture of wide pits and narrow ridges. The heterodontous dentition is a potential autapomorphy of this form. The new specimen is closest in morphology to material described recently from the Callovian of Kirghisia as Sunosuchus sp. It represents the second Middle Jurassic record of the genus, the first crocodile from the Toutunhe Formation, the first substantial crocodile find from the Mesozoic of the Southern Junggar Basin, and the first Middle Jurassic record of Sunosuchus from China. This extends both the paleobiogeographical distribution of the genus in Asia and its stratigraphic distribution in China considerably.