Morphological trends and environment: a case study on Early Cretaceous Myophorelloidea (Bivalvia,Trigoniida) from Neuquén Basin,Argentina

Trigoniide clams were conspicuous components of bivalve faunas in shallow seas during most of the Mesozoic. Morphological trends in different features of shell shape and ornamentation of three related species of myophorelloids from the Agrio Formation (Early Cretaceous of Neuquén Basin, Argentina) that inhabited environments of different hydrodynamic energy conditions are explored in this study by means of a detailed morphometric analysis. Four hydrodynamic energy categories were established for depositional environments, from most (1), to least (4), energetic. General shell shape was characterized by measurements of height, length and width. New quantitative methods were developed to evaluate the distribution of costae along the marginal carina and the divergence of costae along the flank. Morphometric variables were detrended with respect to size, to avoid ontogenetic variability in further analyses. Relative width of the shell increases as environments become higher in hydrodynamic energy; this unusual trend may be interpreted as an anchoring/stabilizing strategy developed by the lineage in shallow marine environments. Trends in ornamentation correspond to more densely distributed costae in environments of higher hydrodynamic energy, a pattern that improves substrate penetration.     

Segmental growth in planulate ammonites: inferences on costal function

Checa, Antonio & Westermann, Gerd E. G. 1989 01 15: Segmental growth in planulate ammonites: inferences on costal function. Lethaia , Vol. 22, pp. 95–100. Oslo. ISSN 0024–1164.
In planulate Ammonitina, the directions of costae and their parts coincide with the growth lines, both being accreted in parallel and subtriangular increments, i.e. segments. This implies that the growing margin was consistently corrugated (plicated) parallel to the edge of the peristome. The adventral separation of the ribs caused by the coiling increased with whorl involution and was compensated for by costal division into primaries and secondaries. We propose that costation of the shallow-water, nekto-benthic plandates reduced the stiffness and increased effective thickness of their growing peristome. Ribs functioned (primarily or secondarily) as a protection for the immature, fragile aperture against predators and impacts.□ Ammonite shell, Jurassic, morphology, growth lines, ornamentation, costae .     

Encrusting patterns and life habit of Mesozoic trigonioids: a case study of Steinmanella quintucoensis (Weaver) from the Early Cretaceous of Argentina

Luci, L. 2010: Encrusting patterns and life habit of Mesozoic trigonioids: a case study of Steinmanella quintucoensis (Weaver) from the Early Cretaceous of Argentina. Lethaia, 10.1111/j.1502‐3931.2009.00210.x. Trigonioid bivalves of the genus Steinmanella Crickmay are abundant at the top of the Vaca Muerta Formation, Neuquén Basin of Argentina, of Early Valanginian age. The species Steinmanella quintucoensis (Weaver) is frequently encrusted by oysters, serpulids and mytilids. Oysters are the most conspicuous encruster, followed by serpulids and then mytilids. A taphonomic, palaeoecological and taxonomic analysis was performed on the encrusting fauna of S. quintucoensis. An analysis of encrusting preference was performed on the basis of differences in ornamentation of the host shell, which was divided in a strongly tubercled flank and a smoother ribbed corselet and escutcheon zone. A higher encrustation frequency was found for the corselet and escutcheon zone, over the larger flank. Possible explanations are differences in the sculpture of each part of the valve, closeness to the respiratory openings of the host, and relation to life position of the trigonioids. In this respect, a palaeoecological analysis of the life position of the genus Steinmanella was made on the basis of functional morphology, encrustation patterns and comparison with related fossil forms as well as living representatives, finding that the most suitable position to explain encrustation patterns and functional morphology is one with the flanks below the water–sediment interface, and the corselets exposed above the substrate. □Early Cretaceous, encrustation, Neuquén Basin, trigonioids.     

Costal strip production and lorica assembly in the large tectiform choanoflagellate Diaphanoeca grandis Ellis

Diaphanoeca grandis posseses a voluminous flask-shaped lorica comprising an outer layer of 12 longitudinal costae and an inner layer of four transverse costae. The cell is suspended just above the centre of the lorica chamber by tentacles that are attached to the anterior transverse ring. The component costal strips are superficially similar although four different strip categories can be distinguished on the basis of length and morphology. Costal strips are produced ‘upside-down’ within the parent cell and accumulated in a close-packed horizontal ring at the top of the inner surface of the collar. The order in which costal strips are produced is consistent, starting with those for the transverse rings, basal to anterior, and then the longitudinal costae, again with the posterior first and the anterior later. Cell division is of the classical tectiform variety with the juvenile cell being inverted and pushed backwards out of the parent lorica. Lorica assembly entails firstly the rotation of the anterior vertical strips so they become horizontal and then their movement backwards under the posterior layer of longitudinal strips. From this time onwards, lorica assembly proceeds in a standard manner with the lorica-assembling tentacles providing a forward and left-handed rotational movement.     

Les Spatangus du Miocène et du Pliocène de l’Ouest de la France

Numerous fragments of spatangoid echinoids have been discovered in the Pliocene deposits of Challans, in Vendée (western France). In spite of the fragmentary data of the samples, a reconstitution of a complete test could be realized using the different fragments and their symetrization. The general shape of the test, and its architectural and ornemental characters allow establishing the presence of the genus Spatangus in western France during the end of Neogene. It allows to precise the biogeography of the genus Spatangus and of the morphological group S. (S.) purpureus on the Atlantic coast after the Messinian crisis. The Pliocene species is compared to the Miocene Spatangus (Phymapatagus) brittanus, abundant in Anjou, Brittany and Touraine. This older species was refered to the subgenus Phymapatagus according to the presumed lack of primary tubercles on its posterior interambulacrum. The discovery of well-preserved specimens, with primary tubercles on every parts of the test, in the Middle Miocene of Brittany allows to refute this subgeneric distinction and to refer the species brittanus to the subgenus Spatangus (Spatangus). The presence of this subgenus in western France is finally confirmed from Middle Miocene to Pliocene.     

Loricate choanoflagellates (Acanthoecida) from warm water seas. VI. Pleurasiga Schiller and Parvicorbicula Deflandre

The loricate choanoflagellate genera Pleurasiga and Parvicorbicula are taxonomically ambiguous. Pleurasiga because of the uncertainty that relates to the true identity of the type species, and Parvicorbicula because too many newly described species over time have been dumped here in lack of better options. While all species currently allocated to the genus Pleurasiga (with the exception of the type species) are observed in our samples from the global warm water belt, the genus Parvicorbicula is represented by just a few and mostly infrequently recorded taxa. Two new species, viz. Pl. quadrangiella sp. nov. and Pl. minutissima sp. nov., are described here. While the former is closely related to Pl. echinocostata, the latter is reminiscent of Pl. minima. Core species of Pleurasiga and Parvicorbicula deviate from the vast majority of loricate choanoflagellates in having both the anterior and the mid-lorica transverse costae located exterior to the longitudinal costae. In Pl. quadrangiella there is no mid-lorica transverse costa but rather a small posterior transverse costa located inside the longitudinal costae. In Pl. minutissima the mid-lorica transverse costa has extensive costal strip overlaps which reveal patterns of costal strip junctions that deviate from the norm.     

Description ofPhyllodiaptomus christineae n.sp. from Thailand, and distinction of two subgenera withinPhyllodiaptomus Kiefer,1936 (Copepoda, Calanoida)

Phyllodiaptomus christineae n.sp. is described from Thailand. It stands out, in the male, by the shape and the armature of the second exopodite-segment of the right P5 and by the elongate apical process and ornamentation of the second exopodite-segment of the left P5; in the female, by the reduced lateral wings of the fifth pediger, and by the form of the genital somite. Together withP. blanci, P. tunguidus andP. longipes, the new species constitutes the blanci-group, here raised to the level of a subgenus (Phyllodiaptomus s.s.) with representatives in Central Asia, China, Borneo and Thailand. A second subgenus (Ctenodiaptomus subgen. nov.) is created to accommodate the four Asian species of the annae-group.     

Loricate choanoflagellates (Acanthoecida) from warm water seas. II. Bicosta,Apheloecion, Campyloacantha,Crucispina, Calliacantha and Saroeca

The main outcome of this and subsequent papers is to provide a baseline survey of heterotrophic protist diversity from warm water marine ecosystems, exemplified by loricate choanoflagellates (Acanthoecida). Genera in focus here (i.e. Bicosta, Apheloecion, Campyloacantha, Crucispina, Calliacantha and Saroeca) possess anterior spines or projections and a posterior pedicel, and have 0, 1 or 2 transverse costae. Longitudinal costae are, with the exception of Campyloacantha, external to transverse costal elements across all genera examined here. We describe here Apheloecion eqpacia sp. nov. and Calliacantha magna sp. nov., both of which are so far distributionally confined to warm water habitats. A ‘form A’ of Bicosta minor is introduced to facilitate the distinction between B. minor sensu stricto and a presumed warm water adapted variant with a posterior lorica chamber twist of the longitudinal costae.     

Adaptive homoeomorphy in the brachiopods Tetractinella Bittner and Cheirothyris Rollier

The Middle Triassic athyraceanTetractinella and the Upper Jurassic terebratellaceanCheirothyris show a close homoeomorphic resemblance in their external shell form. The homoeomorphy is here interpreted as the result of the parallel evolution of an identical adaptive device. Structurally, the homoeomorphy is due to the development of two pairs of long, narrow radial deflections of the commissure, and consequently of two pairs of marginal projections and radial costae on the shell. Functionally, these projections are interpreted as sensory “antennae”, which carried the sensitive mantle edges outwards beyond the rest of the shell, and hence provided the brachiopods with early warning of the approach of potentially harmful agents in the environment.     

Redescription of Triplophysa alticeps (Herzenstein, 1888), the type species of the subgenus Qinghaichthys Zhu, 1981, with notes on its taxonomic position

External morphology and osteology of Triplophysa alticeps, type species of the subgenus Qinghaichthys, is described. A detailed morphological comparison of this species with other species of the genus is also provided. The characteristic traits of T. alticeps include: a short and deep head, neurocranium swollen in the postorbital part, significantly reduced seismosensory system, absence of brushlike aggregations of tubercles on both sides of the head in males, three pectoral radialia, short ventroanal distance, absence of manubrium, and several other features. Possibly, the subgenus Qinghaichthys should be recognized as valid, and should include the species with three radialia of the pectoral fin, a direct contact of the swollen halves of the air-bladder capsule, short swollen head, and without brushlike aggregations of tubercles on the sides of the head in males.     

Redescription and systematic position of Diandongia pista from the Chengjiang Lagerstätte

Diandongia pista Rong is the thickest-shelled and strongly mineralized of all the brachiopods that have been recorded from the Chengjiang Fauna. It is also one of the most common species in the biota. Previous accounts have concentrated largely on the exceptionally preserved soft-bodied anatomy of this species. Here its detailed internal and external shell morphologies are described for the first time, based on BSEM and SEM observations. Its general shell morphology, pseudointerareas, and pustulose ornamentation are most similar to those of the Botsfordiidae, where many species have a Diandongia-like rhombic pattern of pustules in the juvenile apical region only. On the other hand, other aspects of the muscle pattern and the partly smooth adult ornamentation of D. pista is more suggestive of species within the Neobolidae, like Edreja. The mantle canal system in sub-adults of D. pista is comparable to that of the Eoobolidae and Obolidae, whereas the adult vascular system branches peripherally in dichotomy. D. pista may be the earliest representatives possessing some plesiomorphic characters of the Botsfordiidae.     

Pollen morphology of the genus Iris L. (Iridaceae) from Croatia and surrounding area: taxonomic and phylogenetic implications

In Croatia and the surrounding area, the genus Iris is represented with about 20 Alpine-Dinaric, Mediterranean and Pannonian taxa from the subgenera Iris and Limniris. We researched pollen morphology of all taxa by using scanning electron microscopy. All pollen grains are sulcate with few palynological features, which could have taxonomic importance on different classification levels: shape of dry pollen grains; shape, outline and approximate size of hydrated pollen grains, approximate size of the sulcus, and ornamentation of the sulcus membrane and of the exine. At least four pollen types were recognised and taxonomically delimited to the series level: two characterise the subgenus Iris, section Iris (series Elatae and Pumilae), and two the subgenus Limniris, section Limniris (series Laevigatae, Sibiricae and Spuriae). Taxonomic implications of pollen morphology of their critical groups and taxa have been evaluated. Possible phylogenetic implications of pollen morphology of the genus Iris on the Southern European area were suggested: the subgenus Iris is more advanced than the subgenus Limniris; I. graminea seems to be the most primitive member of the subgenus Limniris on the Southern European territory; and pollen morphology of the population of the subspecies I. sibirica subsp. erirrhiza from the Mountain Bjelolasica could represent a link between the subgenera Limniris and Iris in the territory of Southern Europe. The possible pathway of evolution of the genus Iris on the territory of Southern Europe was suggested: from the subgenus Limniris, through the “linked taxon” I. sibirica subsp. erirrhiza from the Bjelolasica Mountain, to the subgenus Iris, series Pumilae, and finally to the series Elatae.     

Effects of shell shape,size, and sculpture in burrowing and anchoring abilities in the freshwater mussel Potamilus alatus (Unionidae)

Because of the sedentary lifestyle of freshwater mussels, studies examining their movement capabilities are scarce. However, the ability to burrow into the substrate and the ability to remain stationary are likely crucial components of their behavioural repertoire. The performance of these different tasks is likely to be affected by the presence of the shell ornamentation characteristic of many mussel species. Previous studies have suggested that shell ornamentation results in a trade‐off between burrowing ability and remaining stationary when an extrinsic force attempts to dislodge it from the substrate once buried. We examined the effect of morphology and shell ornamentation on burrowing performance and anchoring ability by artificially creating shell ornamentation on a relatively smooth‐shelled species (Potamilus alatus). Burrowing behaviours and performance and the force required to dislodge mussels (anchoring ability) were quantified with and without ornamentation. Interestingly, we found that the artificial shell ornamentation had no significant effect on burrowing behaviours and performance or dislodgement force. Burrowing and dislodgement, however, were both highly influenced by shell size and shape. All of the available information suggests that shell size, shape, and sculpture influence burrowing and anchoring in complex ways that needs further examination. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 136–144.     

Syn vivo hydrostatic and hydrodynamic properties of scaphitid ammonoids from the U.S. Western Interior

Scaphitid ammonoids were ubiquitous and significant components of the Western Interior Seaway during the Late Cretaceous. This group is characterized by a recurved hook at maturity that deviates from the juvenile whorls. Such a modification seems counterproductive to active locomotion and to manage a biologically effective orientation that facilitates efficient feeding and swimming. Virtually reconstructed 3D hydrostatic models reveal that the examined mature scaphitids had the capacity for neutral buoyancy while assuming a stable, upward-facing orientation in the water column during life. Models of juvenile Hoploscaphites nicolletii suggest that scaphitid apertures were oriented only slightly more horizontal than adults. The hydrostatic influence of sexual dimorphism was explored with the species Hoploscaphites crassus. The inflated macroconch has a lower stability and higher hydrodynamic drag compared to its microconch counterpart. The effect of shell compression was investigated by comparing H. crassus and the more compressed H. nicolletii. The latter species has a relatively high stability and much less hydrodynamic drag during movement. The mature U-shaped body chamber distributes organismal mass in a way that increases stability, and simultaneously orients the soft body so that propulsive energy is efficiently transmitted into horizontal backwards movement with minimal rocking. Swimming velocities computed from hydrodynamic drag experiments suggest that scaphitids were relatively slow swimmers with compressed forms attaining slightly higher velocities (when scaled by mass). Hydrodynamic lift was investigated with computational fluid dynamics simulations. These experiments revealed that the overall shape of the shell is responsible for significant lift in the upwards direction, which is not heavily influenced by ornamentation. This explains how a reduced soft body can overcome and manage a slightly negatively buoyant condition during life. Therefore, the seemingly cumbersome shape and orientation of the scaphitid morphotype may not have been a hindrance during locomotion.     

Pollen morphology of the Phyllanthus species occurring in the continental United States

Twelve native United States species have been examined. The pollen grains could be divided into five pollen types based on sexine ornamentation, aperture structure, sexine/nexine ratio and sexine 1/sexine 2 ratio. Within these types it was often possible to distinguish the grains of the different species. Two groups of types have been recognized based on the similarities in ornamentation. One group, consisting of the Phyllanthus amarus type, the P. tenellus type and the P. urinaria type, is characterized by the Tilia structure, whereas the second group of types, comprising the P. caroliniensis type and the P. liebmannianus type are microreticulate. The postulation that different subgenera show different pollen types is true in general, but there is one exception: P. niruri, taxonomically belonging to the subgenus Phyllanthus, has pollen grains of the P. caroliniensis type, a type also comprising species from the subgenus Isoclades.     

A revision of xinjiangchelyid turtles from the Late Jurassic of Sichuan Basin,China

The type specimens of the Jurassic turtles from the Sichuan Basin (China) previously referred to plesiochelyid Plesiochelys are revised, which confirm that they belong to the family Xinjiangchelyidae. The study of a large number of additional shell material shows, as the dominant group, the Xinjiangchelyidae were greatly diversified in the Late Jurassic of the Sichuan Basin. By the absence of mesoplastron and other shell characters, Chengyuchelys baenoides is moved to Xinjiangchelyidae and considered as a valid taxon. Of the xinjiangchelyids from the Late Jurassic of Sichuan Basin, four genera are recognized: Chengyuchelys, Tienfuchelys, Yanduchelys and cf. Protoxinjiangchelys. The phylogenetic analysis results in that Chengyuchelys includes C. baenoides, C. latimarginalis and C. radiplicatus, and Tienfuchelys consists of T. tzuyangensis, T. chungkingensis and T. zigongensis. All xinjiangchelyids from the Sichuan Basin are more primitive than Xinjiangchelys in the plastron sutured to the carapace.     

Diversity of Middle Jurassic Turtles from the Berezovsk Quarry Locality,Krasnoyarsk Region,Russia: Morphology and Histological Study

Abstract—Morphology and histology of several fragmentary turtle specimens from the Middle Jurassic locality in the Berezovsk quarry (Krasnoyarsk Region, Russia) are described, including Testudines indet. 1 (costal VIII), Testudines indet. 2 (two ornamented shell fragments), and Testudines indet. 3 (distal part of a humerus), and also skeletal elements of Annemys sp. (Xinjiangchelyidae) represented by mass material in the same locality. It is shown that Testudines indet. 1 and 3 probably belong to one or two taxa of basal aquatic turtles, while Testudines indet. 2 is most likely an abnormal Annemys sp. The presumable presence of basal turtles in the Berezovsk Quarry Assemblage agrees with the fact that they are present in other Middle Jurassic turtle assemblages of Asia.     

Size and age composition of populations and growth of Mytilus trossulus (Bivalvia: Mytilidae) in the subtidal area of western Kamchatka

Fairly large Mytilus trossulus beds were found in the subtidal zone at depths to 40 m off the western coast of Kamchatka. The size and age composition of local populations and growth rates of M. trossulus in this region and at Atlasova Island were studied. Significant variability of the shell shape of mollusks was found. In the western Kamchatka subtidal, M. trossulus grew faster than in the northern Kuril Islands and eastern Kamchatka. Mussels attained commercial size (50 mm in shell length) in the fourth year of life in the former case and in the fifth-sixth year in other cases. Mollusks of different ages, from 1 to 8–9 year olds, were present in western Kamchatka populations; i.e., juvenile recruitment takes place regularly, while growth rates vary. Growth and population structure of M. trossulus are discussed in relation to the habitat conditions on the western Kamchatka shelf.     

A new type of test wall in the Late Cretaceous (Late Santonian-Campanian) heterohelicid planktic foraminifera

The first Cretaceous serial planktic foraminifer (family Heterohelicidae Cushman, 1927) with simple-ridged test wall is reported from the uppermost Santonian-lower Campanian sediments of the Deep Sea Drilling Project Site 463 (Mid-Pacific Mountains, equatorial Central Pacific). Hendersonites pacificus n. sp. is characterized by the reduced ornamentation over the last pairs of chambers and strong peripheral costae lining the periphery with test wall flexure. This species evolved from H. carinata (Cushman, 1938) of the upper Santonian-Campanian, a frequently reported species from the Atlantic Ocean, Gulf of Mexico and Western Tethyan Realm.