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Attachment Structure (attachment + structure)

Distribution by Scientific Domains
Earth and Environmental Science62%

Selected Abstracts

New type of egg attachment structure in Ephemeroptera and comparative analysis of chorion structure morphology in three species of Ephemerellidae

ACTA ZOOLOGICA, Issue 1 2009
N. Ubero-Pascal
Abstract Ephemeroptera eggs vary greatly in their morphology, a characteristic that has been used to solve systematic problems. The eggs of Ephemerellidae may be considered among the most studied in mayfly families, especially with regard to the number of species for which they have been described (approximately 32 species corresponding to 12 genera). However, this study provides new details of the egg morphology of three species of this family, Serratella ignita (Poda 1761), S. spinosa (Ikonomov 1961) and Torleya major (Klapalek 1905). The main finding was that the morphology and organization of the lateral attachment structures do not resemble the type normally associated with,knob terminated coiled thread' (KCT). The particular characteristics of this structure, never before described for Ephemeroptera, led us to propose a new type of attachment structure, the ,multithread-folded with terminal fibre cluster' (MFT). We also provide a detailed description of the chorion morphology of the eggs of the three species, identifying a tear-shaped variation in the oval sperm guide and confirming the type III polar caps in the two species of Serratella Walsh, 1862. [source]

The root of the problem: palaeoecology of distinctive crinoid attachment structures from the Silurian (Wenlock) of Gotland

LETHAIA, Issue 4 2007
STEPHEN K. DONOVAN
The holdfast (attachment structure) is the most understudied aspect of the palaeoecology of the endoskeleton of fossil crinoids. A new collection of well-preserved holdfasts from a recently reopened quarry at Hunninge, Gotland, in Homerian (upper Wenlock) strata includes several morphologies. The most common are terminal dendritic radicular holdfasts (TDRHs) that may be derived from the cladid Ennallocrinus d'Orbigny. These have a consistent morphology of five, equally spaced, long radices that spread across the sea floor. These crinoids were gregarious, and TDRHs in a group commonly show the same radice orientations. The radices have a large axial canal compared with those of modern crinoids; each included, at least, nervous tissues. Taken together, these features suggest that, apart from attachment, these distinctive TDRHs may have served a sensory function. Other holdfasts in this assemblage also show monospecific aggregations, perhaps suggesting biochemical attraction such as that shown by certain other sessile invertebrates such as barnacles. [source]

Shell structure, ontogeny and affinities of the Lower Cambrian bivalved problematic fossil Mickwitzia muralensis Walcott, 1913

LETHAIA, Issue 4 2004
UWE BALTHASAR
Exceptionally preserved carbonate- and shale-hosted Mickwitzia muralensis from the Lower Cambrian Mural Formation, southern Canadian Rocky Mountains, complement one another to yield an unusually complete account of its ontogeny, ecology and phylogenetic relationships. The shell of M. muralensis is composed of dense phosphatic layers interspersed with porous organic-rich layers. At the insertion of shell-penetrating tubes, shell layers deflect inwards to produce inwardly pointing cones. The tubes are interpreted as having hosted setae that were secreted by outer-epithelial follicles. Follicular setae also occurred at the mantle margin, where they were oriented within the plane of the shell as in modern brachiopods. During ontogeny, the initial setae oriented in the plane of the shell occurred before the first shell-penetrative setae. In the juvenile and early-mature stages of shell secretion, a posterior opening was present between both valves and was used for the protrusion of an attachment structure. In the late-mature shell, this opening became fixed in the ventral valve. Based on the posterior margin and the shell microstructure, a close relationship between Mickwitzia and the paterinids is proposed with differences interpreted as heterochronic. The shell-penetrative setal apparatus of M. muralensis is distinct from that previously described of Micrina, though both types are conceivably homologous to adult and juvenile setae of modern brachiopods. [source]

New type of egg attachment structure in Ephemeroptera and comparative analysis of chorion structure morphology in three species of Ephemerellidae

ACTA ZOOLOGICA, Issue 1 2009
N. Ubero-Pascal
Abstract Ephemeroptera eggs vary greatly in their morphology, a characteristic that has been used to solve systematic problems. The eggs of Ephemerellidae may be considered among the most studied in mayfly families, especially with regard to the number of species for which they have been described (approximately 32 species corresponding to 12 genera). However, this study provides new details of the egg morphology of three species of this family, Serratella ignita (Poda 1761), S. spinosa (Ikonomov 1961) and Torleya major (Klapalek 1905). The main finding was that the morphology and organization of the lateral attachment structures do not resemble the type normally associated with,knob terminated coiled thread' (KCT). The particular characteristics of this structure, never before described for Ephemeroptera, led us to propose a new type of attachment structure, the ,multithread-folded with terminal fibre cluster' (MFT). We also provide a detailed description of the chorion morphology of the eggs of the three species, identifying a tear-shaped variation in the oval sperm guide and confirming the type III polar caps in the two species of Serratella Walsh, 1862. [source]

The root of the problem: palaeoecology of distinctive crinoid attachment structures from the Silurian (Wenlock) of Gotland

LETHAIA, Issue 4 2007
STEPHEN K. DONOVAN
The holdfast (attachment structure) is the most understudied aspect of the palaeoecology of the endoskeleton of fossil crinoids. A new collection of well-preserved holdfasts from a recently reopened quarry at Hunninge, Gotland, in Homerian (upper Wenlock) strata includes several morphologies. The most common are terminal dendritic radicular holdfasts (TDRHs) that may be derived from the cladid Ennallocrinus d'Orbigny. These have a consistent morphology of five, equally spaced, long radices that spread across the sea floor. These crinoids were gregarious, and TDRHs in a group commonly show the same radice orientations. The radices have a large axial canal compared with those of modern crinoids; each included, at least, nervous tissues. Taken together, these features suggest that, apart from attachment, these distinctive TDRHs may have served a sensory function. Other holdfasts in this assemblage also show monospecific aggregations, perhaps suggesting biochemical attraction such as that shown by certain other sessile invertebrates such as barnacles. [source]

Survival of crinoid stems following decapitation: evidence from the Ordovician and palaeobiological implications

LETHAIA, Issue 4 2001
STEPHEN K. DONOVAN
It was recently discovered that the stems of extant crinoids may survive after detachment of the crown, presumably feeding by the absorption of nutrients through the ectoderm. Previously, only one analogous, albeit morphologically dissimilar, pattern of crownless survival has been recognized from the fossil record. Certain Upper Ordovician (Cincinnatian) crinoid pluricolumnals from Kentucky, Ohio and Indiana, derived from the disparids Cincinnaticrinus spp., have rounded terminations reminiscent of some modern bourgueticrinid overgrowths. Such specimens have hitherto been interpreted as distal terminations of mature individuals that have become detached from their attachment structures and taken to an eleutherozoic existence. However, it is considered more probable that they represent overgrowths of the column following predatory decapitation. If this new interpretation is correct, then post-decapitation survival of crinoid stems is now recognized for most of the history of the crinoids, ,lethal' predation on crinoid crowns occurred at least as early as the Late Ordovician and ancient crinoid populations can no longer be determined merely by counting crowns. [source]

SOME LESSER KNOWN FEATURES OF THE ANCIENT CEPHALOPOD ORDER ELLESMEROCERIDA (NAUTILOIDEA, CEPHALOPODA)

PALAEONTOLOGY, Issue 3 2007
BJÖRN KRÖGER
Abstract:, Three specimens of the small breviconic ellesmeroceratid Paradakeoceras minor Flower, 1964 from the Tremadocian of the New York area preserve the annular elevation and muscle scars in moulds of the body chamber. The annular elevation is positioned at the base of the body chamber and is wider on the convex side of the shell than on the concave side. Multiple paired muscle scars can be seen within this annular elevation. A well-preserved body chamber of the breviconic ellesmeroceratid Levisoceras cf. edwardsi Ulrich, Foerste and Miller is described. Its body chamber shows a strong anterior,posterior asymmetry, which is common within the Ellesmeroceratida. The shape of the body chamber and of the soft body attachment structures has led to a reconstruction of an ellesmeroceratid soft body that is organized like a primitive conchiferan mollusc. Based on this reconstruction, a tryblidian cephalopod ancestor is supported. An evolutionary scenario is reconstructed from an ancestral nautiloid that is stretched along the anterior,posterior axis, and has serially arranged shell muscles and a small mantle cavity, towards a modern cephalopod with a dorsal,ventral body orientation, reduced number of shell muscles and a large mantle cavity. [source]