Affinities of the alleged earliest Cambrian gastropod Aldanella

2013 ◽  
Vol 91 (12) ◽  
pp. 914-923 ◽  
Author(s):  
Jerzy Dzik ◽  
Dawid Mazurek
Keyword(s):  
Shell Morphology ◽  
Skewed Distribution ◽  
Phylogenetic Position ◽  
Soft Body ◽  
Middle Cambrian ◽  
Small Shelly Fossils ◽  
Embryonic Shell ◽  
Mode Of Life ◽  
Early Palaeozoic ◽  
Mature Size

Unlike true Palaeozoic gastropods, but similar to some coeval hyoliths, the cup-like hemispherical embryonic shell of Aldanella attleborensis (Shaler and Foerste, 1888) from the earliest Cambrian (early Tommotian) Erkeket Formation of northern Siberia bears a mucro. Also, the pattern of mortality, with right-skewed distribution and a peak at about 1.0 mm diameter, is not similar to that of early Palaeozoic gastropods; there is no evidence of metamorphosis that would end the pelagic larval stage of ontogeny. Specimens of larger size are rare in samples of phosphatized “small shelly fossils” but are known in related species of the genus, of up to 3–5 mm diameter. A phosphatized soft body is preserved in a few specimens of A. attleborensis, one bearing possible chaetae of about 5 μm diameter. Such bunches of chaetae arming locomotory organs were earlier identified in the genus Pelagiella Matthew, 1895, a more derived member of the same lineage. It shares with the genus Aldanella Vostokova, 1962 also the mucronate embryonic shell and acicular aragonitic shell wall microstructure. The presence of chaetae-bearing organs suggests pelagic mode of life of pelagiellids at maturity. Middle Cambrian Pelagiella shells reached 7 mm in diameter, suggesting evolutionary increase in mature size. Embryonic shell morphology, wall microstructure, and the presence of locomotory organs with a fan of chaetae contradicts gastropod, and even conchiferan affinity of the pelagiellids, but together with the pattern of ontogeny conforms to the enigmatic Palaeozoic hyoliths. They differ in having opercula closing the shell apertures and in lacking evidence of chaetae. The helens, paired apertural appendages of possible locomotory function occurring in apertures of some of them, do not reveal any similarity to chaetae in their development. We propose classifying the order Pelagiellida in the class Hyolitha rather than in the class Gastropoda, until its phylogenetic position is clarified. Such understood hyoliths may represent the earliest stage in evolution of molluscs, immediately following initial diversification of the spiralians (lophotrochozoans) into phyla.

Ontogenetic change and intra-specific variation of shell morphology in the Cretaceous nautiloid (Cephalopoda, Mollusca) Eutrephoceras clementinum (d'Orbigny, 1840) from the Ariyalur area, southern India

2009 ◽  
Vol 83 (3) ◽  
pp. 365-378 ◽  
Author(s):  
Ryoji Wani ◽  
Krishnan Ayyasami
Keyword(s):  
Shell Morphology ◽  
Southern India ◽  
Shell Shape ◽  
Morphometric Study ◽  
Central Position ◽  
Ontogenetic Change ◽  
Allometric Relationship ◽  
Shell Diameter ◽  
Mode Of Life ◽  
Specific Variation

Morphometric analyses of shell morphology in the Cretaceous nautiloid Eutrephoceras clementinum (d'Orbigny, 1840) (Cephalopoda, Mollusca) from the Ariyalur area, southern India, reveal ontogenetic change from hatching to maturity as well as intra-specific variation in shell morphology. the shell breadth has a negative allometric relationship with shell diameter and with whorl height, and the umbilicus diameter has a positive allometric relationship with shell diameter. This shows that shell shape became relatively thinner with less variation, and the umbilicus diameter became relatively broader with growth. the siphuncle position moves from a dorso-central to ventro-central position with growth. A constriction was recognized on the early whorl at 20 mm in shell diameter, and the interval angles of succeeding septa were changed at the 8th septum, indicating that they hatched at this stage. the bending of umbilical walls of apertures toward the center of coiling suggests that E. clementinum attained maturity at about 115 mm in shell diameter. the comparison of the shell morphology of E. clementinum with that of E. bouchardianum (d'Orbigny, 1840) reported in the literature clarifies their difference in whorl shape and umbilical size, especially in the adult stage. This kind of morphometric study of nautiloids is essential for elucidating their adaptive designs for environment and mode of life, functional shell morphology, taxonomy, phylogeny, and evolution.

scholarly journals Cambrian microfossils from the Tethyan Himalaya

2016 ◽  
Vol 90 (1) ◽  
pp. 10-30 ◽  
Author(s):  
Ian R. Gilbert ◽  
Nigel C. Hughes ◽  
Paul M. Myrow
Keyword(s):  
Indian Subcontinent ◽  
Age Determination ◽  
Acid Digestion ◽  
Middle Cambrian ◽  
Late Cambrian ◽  
Small Shelly Fossils ◽  
Stage 4 ◽  
Stratigraphic Ranges ◽  
A New Species ◽  
Tethyan Himalaya

AbstractCambrian biostratigraphy of the Indian subcontinent is best documented from the Parahio Formation of the Tethyan Himalaya. Recently established trilobite biostratigraphy shows that the formation encompasses the latest part of unnamed Stage 4 and much of unnamed Stage 5. A variety of small shelly fossils have been recovered via acid digestion of carbonate beds and include tetract and pentact hexactinellid sponge spicules, chancelloriid spicules belonging to Chancelloria sp. and a new species, Archiasterella dhiraji, shells of an helcionelloid comparable to Igorella maidipingensis, a meraspid ptychopariid trilobite, the tubular Cupitheca sp., a poorly preserved hyolith, and an assortment of spinose microfossils of uncertain affinity. These newly recovered microfossils are consistent with the trilobite-based lower and middle Cambrian age determination and do not support a late Cambrian age for the top of the Parahio Formation advocated in some recent literature. The microfossils reported herein significantly expand the known diversity of such fossils from Cambrian strata in the Himalayan region, and allow for comparison of this fauna with others from Gondwanaland and elsewhere. Integration with trilobite data indicate that the stratigraphic ranges of many small shelly fossils described in this study are greater than previously recognized.

The enigmatic bivalve genus Paramya (Myoidea: Myidae): symbiotic association of an East Asian species with spoon worms (Echiura) and its transfer to the family Basterotiidae (Galeommatoidea)

2016 ◽  
Vol 97 (7) ◽  
pp. 1447-1454 ◽  
Author(s):  
Ryutaro Goto ◽  
Hiroshi Ishikawa ◽  
Yoichi Hamamura
Keyword(s):  
Coastal Waters ◽  
East Asian ◽  
Shell Morphology ◽  
The Other ◽  
Phylogenetic Position ◽  
Symbiotic Association ◽  
Morphological Examination ◽  
The Family ◽  
The Seto Inland Sea ◽  
Molecular Phylogenetic

Paramya is an enigmatic genus of Myidae (Bivalvia: Heterodonta: Myoidea) that includes three uncommon species: Paramya subovata (Conrad, 1845), Paramya recluzi (A. Adams, 1864) and Paramya africana Cosel, 1995. Paramya subovata is known as a commensal living in the burrow of the spoon worm Thalassema hartmani Fisher, 1947 (Annelida: Echiura: Thalassematidae), in North American coastal waters. However, the biology of the other two species remains unknown. In this study, we found P. recluzi living in the burrows of the two thalassematid echiuran species, Ikedosoma gogoshimense (Ikeda, 1904) and Arhynchite hayaoi Tanaka & Nishikawa, 2013, in intertidal flats in the Seto Inland Sea, Japan. Paramya recluzi was embedded in the burrow wall with its short siphons protruding into the host burrow lumen for respiration and filter feeding. To determine the phylogenetic position of P. recluzi, we performed a molecular phylogenetic analysis using the 18S, 28S, COI and H3 genes. Molecular analysis showed that P. recluzi belongs not to the family Myidae, but to the genus Basterotia (Galeommatoidea: Basterotiidae). Morphological examination of P. recluzi revealed that this species has many similarities with Basterotia (e.g. a single cardinal tooth on each valve and short siphons surrounded by tentacles). Thus, we propose that this species should be transferred from the genus Paramya to Basterotia. In addition, we also suggest that the other two species of Paramya (P. subovata and P. africana) should be transferred to the family Basterotiidae based on their shell morphology, anatomy and ecological characteristics.

Opertochasma somaensis n. sp. (Bivalvia: Pholadidae) from the Upper Jurassic in Japan: a perspective on pholadoidean early evolution

2011 ◽  
Vol 85 (3) ◽  
pp. 478-488 ◽  
Author(s):  
Takuma Haga ◽  
Tomoki Kase
Keyword(s):  
New Species ◽  
Late Jurassic ◽  
Upper Jurassic ◽  
Shell Morphology ◽  
Middle Latitudes ◽  
Mode Of Life ◽  
Floral Diversification ◽  
History Of ◽  
Wood Borer

The evolutionary history of the major boring-bivalve superfamily Pholadoidea remains unclear. Opertochasma somaensis n. sp., preserved in situ in fossilized wood from upper Kimmeridgian to lower Tithonian strata within the Upper Jurassic shallow marine Nakanosawa Formation, northeast Japan, is described. This new species represents one of the oldest body fossils of pholadoidean boring-bivalves and the first fossil record from the Jurassic in the circum-Pacific regions. The authochthonous occurrence in fossilized wood, the presence of microscopic file-like sculpture on the anterior shell slope, the short clavate burrow, and other shell features demonstrate that O. somaensis n. sp. was a filter-feeding, obligate wood-borer with anterior-boring locomotion, and also that the complex shell morphology unique to Pholadoidea was established by the Late Jurassic. The documentation of the new species and taxonomic review on the Jurassic species previously described, show that the superfamily Pholadoidea was widely distributed along the Northern Hemisphere middle latitudes in the latest Jurassic. The Pholadoidea likely evolved by exploiting woody substrata which had become abundant during the Late Jurassic with floral diversification in the middle latitudes. It is notable that the xylophagous mode of life, referable to modern Teredinidae and Xylophagaidae, was most probably established in the Jurassic and provided an important background for the establishment of chemosynthesis-based, sunken wood-associated communities.

Morphology, morphoclines and a new classification of the Pteriomorphia (Mollusca: Bivalvia)

1978 ◽  
Vol 284 (1001) ◽  
pp. 345-365 ◽  
Keyword(s):  
Cladistic Analysis ◽  
Early Carboniferous ◽  
Published Data ◽  
Prismatic Structure ◽  
New Family ◽  
Mantle Edge ◽  
Mode Of Life ◽  
Homologous Structure ◽  
Early Palaeozoic

Two morphological paradigms have long been used in comparative anatomical studies of bivalves: (1) the primary ligament is three-layered, with the layers corresponding to three shell layers; and (2) the primary mantle edge is composed of three folds with clearly defined functions. The results of studies of larval development indicate, on the contrary, that the primary ligament is completely organic. Calcified, fibrous ligamental material develops from lamellar material near areas of contact between ligament and shell, and development of the fibrous portions then proceeds toward the midline, finally achieving in many lineages a continuous fibrous bridge between valves. Furthermore, these results suggest that the mantle edge in the Bivalvia is primarily twofold and that the only clearly homologous structure between major groups is the periostracal groove itself. These morphological concepts, with other new and previously published data on shell ultrastructure, ligaments, mantle edges, ctenidia, palps, lips, stomachs, muscles, and photoreceptors, lead to a new picture of the evolution of primitive and derived character states in groups previously included in a subclass Pteriomorphia. Furthermore, a cladistic analysis of these data allows predictions of the morphology of ancestors which can be tested by reference to the preserved morphology and sequence of fossils. A new phylogenetic classification separates these groups into three superorders within the subclass Autobranchia: Isofilibranchia (mytiloids), Prionodonta (arcoids), and Pteriomorphia. The most complex radiation has been in the Pteriomorphia. Three orders originated in the early Palaeozoic: Pterioida, Limoida, and Ostreoida. The Pterioida and Ostreoida developed monomyarian, pleurothetic states independently, and each order developed its own mode of shell secretion. Further differentiation in the order Ostreoida occurred in the mid-Palaeozoic, producing two suborders, the Ostreina and Pectinina, both of which had already developed foliated calcitic ultrastructure from simple prismatic structure. By the early Mesozoic, the Ostreina had given rise to three extant superfamilies - the Ostreacea (true oysters), Dimyacea, and Plicatulacea - through atrophy of the foot, the assumption of a pleurothetic state on either the left or right side, and early obligate cementation. The Pectinina, through retention of the foot and the assumption of a pleurothetic mode of life, had evolved before the late Palaeozoic to the Anomiacea and Pectinacea. Within the superfamily Pectinacea, four extant families have origins ranging from early Carboniferous to Cretaceous in age: Propeamussiidae, Pectinidae, Syncyclonemidae, and Spondylidae. The new family Syncyclonemidae, which contains a genus long assumed to have become extinct at the end of the Cretaceous, is here recognized in the Recent and late Pleistocene on opposite sides of the Earth. With regard to extinct groups, many genera previously assigned to the Pteriacean family Malleidae belong in the Ostreacea on the basis of shared derived character states. Incorporation of these taxa as well as the Dimyacea in the Ostreina suggests that oysters have a dimyarian, possibly non-pleurothetic, origin and cannot have evolved from forms like the Pseudomonotids, which retained their foot and became pleurothetic. The new name Buchiacea is introduced for a set of extinct taxa within the suborder Pectinina including the Buchiidae, Monotidae, Oxytomidae, and Pseudomonotidae of previous authors. Derivation of this group is from the common ancestry of the Anomiacea and Pectinacea. The extinct Palaeozoic Aviculopectinidae, Pterinopectinidae, Deltopectinidae, and Leiopectinidae are grouped in a superfamily Aviculopectinacea, which also appears to have branched from the early ancestry of the Pectinina.

Evolution of shell apertural barriers in viviparous land snails (Gastropoda: Pulmonata: Clausiliidae)

2014 ◽  
Vol 92 (3) ◽  
pp. 205-213 ◽  
Author(s):  
A. Sulikowska-Drozd ◽  
M. Walczak ◽  
M. Binkowski
Keyword(s):  
Reproductive Strategies ◽  
Three Dimensional ◽  
Land Snails ◽  
Shell Morphology ◽  
Shell Size ◽  
X Ray ◽  
Egg Retention ◽  
Embryonic Shell ◽  
Selective Forces ◽  
Size At Birth

Apertural barriers in the snail shell were frequently associated with adaptation against predators or with reducing water loss. Yet formation of teeth occluding the aperture is costly and potentially precludes life-bearing reproduction. In viviparous species, a trade-off between the shell aperture size and the embryo shell size at birth is expected. This hypothesis was tested in clausiliids, land snails with strong apertural barriers, that displayed a range of reproductive strategies (oviparity, egg retention, viviparity). We assessed their three-dimensional internal shell morphology by means of X-ray microcomputed tomography (XMT). The data were later analysed with a specially designed algorithm that mimics the movement of the spherical embryonic shell in the lumen of the parental shell. It appeared that viviparous reproduction required the widening of the passage through the ultimate whorl, but that did not necessarily lead to a reduction of apertural barriers. This provides an example of evolutionary compromise between enhanced fitness of the offspring owing to a long gestation period and survival of the parent. Clausiliids might be selected for viviparity only if other selective forces were released, e.g., in areas where desiccation was not a major threat. This hypothesis is in congruence with the distribution of viviparous clausiliids in Europe.

Burgess Shale-type preservation of both non-mineralizing and ‘shelly’ Cambrian organisms from the Mackenzie Mountains, northwestern Canada

1996 ◽  
Vol 70 (6) ◽  
pp. 893-899 ◽  
Author(s):  
N. J. Butterfield ◽  
C. J. Nicholas
Keyword(s):  
Granular Material ◽  
Surface Texture ◽  
Hydrofluoric Acid ◽  
Burgess Shale ◽  
Middle Cambrian ◽  
Small Shelly Fossils ◽  
Polygonal Surface ◽  
Acid Processing ◽  
Mackenzie Mountains ◽  
Type Preservation

Lower to Middle Cambrian shales of the Mount Cap Formation in the Mackenzie Mountains, northwestern Canada, host a variety of Burgess Shale-type macrofossils, including anomalocarid claws, several taxa of bivalved arthropod, articulated hyolithids, and articulated chancelloriids. Hydrofluoric acid processing has also yielded a broad range of organic-walled fossils, most of which are derived from forms more typically known as shelly fossils; e.g., trilobites, inarticulate brachiopods, small shelly fossils (SSF), hyolithids, and chancelloriids. Organic-walled hyolithids include conchs, opercula and helens; the proximal articulation of the helens is erosive, suggesting that they were formed “instantaneously” and periodically replaced. Organic-walled chancelloriid sclerites exhibit a polygonal surface texture and an inner “pith” of dark granular material with distally oriented conoidal divisions; such a pattern is similar to that seen in the fibers of some modern horny sponges and points to a poriferan relationship for the chancelloriids. The robust nature but minimal relief of most of these fossils suggests that primary biomineralization was minimal.

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