Relatively recent evolution of an unusual pattern of early embryonic development (long germ band?) in a South African onychophoran,Opisthopatus cinctipes Purcell (Onychophora: Peripatopsidae)

During embryonic development the process of segment formation in both families of the Onychophora, the Peripatidae and the Peripatopsidae, follows an essentially similar pattern with the exception of the South African peripatopsid, Opisthopatus cinctipes Purcell. In all other species in which development has been described, paired lateral halves of the embryo, separated by extra-embryonic ectoderm, develop as thickened bands on the surface of the blastoderm coincident with the appearance of the mouth and anus. The bands quickly differentiate paired segmental swellings with intersegmental grooves. The body elongates by proliferation from a posterior growth zone. During this process, presumptive mesoderm, located posteriorly in the early embryo, proliferates and moves anteriorly to form two lateral bands of mesodermal cells which segment during their forward growth into an anterior-posterior sequence of paired somites. In O. cinctipes the embryo elongates without any visible external or internal segment boundaries. In the elongating embryo only ectoderm and endoderm layers are present. Only after elongation has occurred are mesodermal somites formed. Allozyme analysis indicates that O. cinctipes diverged from the other South African genus Peripatopsis Pocock, with in the last 30 Myr.     

Unmasking alpha diversity,cladogenesis and biogeographical patterning in an ancient panarthropod lineage (Onychophora: Peripatopsidae: Opisthopatus cinctipes) with the description of five novel species

Speciation and biogeographical patterning in the velvet worm Opisthopatus cinctipes was examined under a null hypothesis that numerous discrete lineages are nested within the species. A total of 184 O. cinctipes specimens, together with a single specimen of each of the two congeneric point endemic sister species (O. roseus and O. herbertorum), were collected throughout the forest archipelago in the Eastern Cape, KwaZulu‐Natal and Mpumalanga provinces of South Africa. All specimens were sequenced for two partial mitochondrial DNA loci (COI and 12S rRNA), while a single specimen from each locality was sequenced for the nuclear 18S rRNA locus. Evolutionary relationships were assessed using maximum‐likelihood and Bayesian inferences, while divergence time estimations were conducted using BEAST. A Bayesian species delimitation approach was undertaken to explore the number of possible novel lineages nested within Opisthopatus, while population genetic structure was examined for the COI locus using ARLEQUIN. Phylogenetic results revealed that O. cinctipes is a species complex comprising seven geographically discrete and statistically well‐supported clades. An independent statistical approach to species delimitations circumscribed ca. 67 species. Results from divergence time estimation and rate constancy tests revealed near constant net diversification occurring throughout the Eocene and Oligocene with subdivision of ranges during the Miocene. Gross morphological characters such as leg pair number within O. cinctipes were invariant, while dorsal and ventral integument colour was highly polymorphic. However, scanning electron microscopy revealed considerable differences both between and within clades. The caveats associated with both morphological and algorithmic delineation of species boundaries are discussed. The five novel Opisthopatus species are described.     

Ultrastructural Analysis of the Sensilla of Austroperipatus aequabilis Reid, 1996 (Onychophora,Peripatopsidae)

The head of Austroperipatus aequabilis bears five types of sensilla. which were examined by electron microscopy. They differ from each other in position, shape of outer sensory elements and cuticular socket structures. Thus, we distinguish sensilla with sensory hairs, sensilla with sensory bulbs, cone-shaped sensilla. sensilla with sensory bristles, and sensilla of the lips. They are composed of up to 15 cells, which can he separated into four cell types. The most frequent cell type is the bipolar receptor cell that occurs in all sensilla. The apical surface of this primary receptor cell is characterized by one or two partly branched cilia with a basal 9 × 2 + 0 pattern of microtubules. A modified bipolar receptor cell was found in all sensilla bearing a sensory peg except for the sensilla equipped with sensory bristles. The apical dendrite extends to a long pale process which exclusively contains mitochondria and single microtubules. In all sensilla examined in this study at least one supporting cell occurs which is characterized by parallel microvilli. An additional function of this cell type as a part of the stimulus-conducting system is possible. In the sensillum with a sensory bulb two kinds of supporting cells occur. A unique cell type with an upside down position has regularly been found in all sensilla bearing a sensory peg. Apart from the sensilla they also occur within the labial epidermis. Since most sensilla contain several different receptor cells, they can be considered as complex sense organs. © 1998 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd. All rights reserved     

Zur Entstehung der Vogelarten

Ohne Zusammenfassung     

The female genital system of Ooperipatellus decoratus (Onychophora, Peripatopsidae): an ultrastructural study

The female genital system of the oviparous peripatopsid Ooperipatellus decoratus consists of an ovary, oviducts equipped with receptacula seminis and additional pouches, uteri, and a vagina. It is examined using transmission and scanning electron microscopy. The ovary is made up of paired ovarian tubes united anteriorly and posteriorly and differentiated into a sterile dorsal part and a fertile ventral part with exogenous oocytes. Fertilization presumably occurs in the oviducts once the oocytes pass the receptaculum seminis. Although the receptacula seminis have been reported to occur in juvenile O. decoratus females only, the present study reveals that they are present in adult females as well. Their wall consists of a cuboidal epithelium covered with a thin collagen-muscle layer. The additional pouches are projections of the oviducts facing the receptacula seminis. They are distally closed to the haemocoel by a flattened epithelium and lack external muscle cells. A thin collagen layer is only found proximally. The uteri are characterized by a columnar epithelium with folded cell membranes allowing extension of the uteri, thus facilitating the passage of the large uterine eggs towards the vagina. Another dominating feature of the uteri is a distally increasing secretory production, which probably contributes to chorion development. Cilia occurring along the entire length of the uteri are considered to assist in the transport of eggs towards the vagina.     

Zur Entstehung der Mimikry der Kuckuckseier

Ohne Zusammenfassung     

Ultrastructure of the eggshell and its formation in Planipapillus mundus (Onychophora: Peripatopsidae)

Although the majority of onychophorans are viviparous or ovoviviparous, oviparity has been described in a number of species found exclusively in Australia and New Zealand. Light microscopy and scanning and transmission electron microscopy were used to examine developing eggs and the reproductive tract of the oviparous Planipapillus mundus. Deposited eggs and fully developed eggs dissected from the terminal end of the uteri have an outer thick, slightly opaque chorion, and an inner thin, transparent vitelline membrane. The chorion comprises an outermost extrachorion, sculptured with domes equally spaced over the surface; a middle exochorion, with pores occurring in a pattern of distribution equivalent to that of the domes of the extrachorion above; and an innermost, thick endochorion consisting of a spongelike reticulum of cavities comparable to the respiratory network found in insect eggs. The vitelline membrane lies beneath the chorion, from which it is separated by a fluid‐filled space. The vitelline membrane tightly invests the developing egg. Examination of oocytes in the ovary and developing eggs at various stages of passage through the uterus indicate that the majority of chorion deposition occurs in the midregion of the uterus, where vast networks of endoplasmic reticulum are present in the columnar epithelium. The vitelline membrane, however, is believed to begin its development as a primary egg membrane, surrounding the developing oocytes in the ovary. The vitelline membrane is transformed after fertilization, presumably by secretions from the anterior region of the uterus; hence, it should be more accurately referred to as a fertilization membrane. Aspects of the reproductive biology of P. mundus are also included. J. Morphol., 2008. © 2008 Wiley‐Liss, Inc.     

Morphological, cytogenetic and allozymic variation within Cephalofovea (Onychophora: Peripatopsidae) with descriptions of three new species

Variation within and between populations of Cephalofovea (Peripatopsidae) has been examined by allozyme, karyological and morphological analyses. Four groups are recognized on the basis of allozyme electrophoresis. One group includes specimens from the type locality of the only described species of the genus, C. tomahmontis. While karyotypic and morphological character states show considerable inter-group variation, the distributions of these states among groups are not concordant when different characters are compared. However, each group of populations is uniquely defined by the full suite of character states it possesses. The four groups are recognized here as distinct species with three species described as new.     

Zur Entstehung der Gemmulae bei Ephydatia fluviatilis L. (Porifera)

Zusammenfassung Gemmula-Anlagen des Süßwasserschwamms Ephydatia fluviatilis bestehen aus Archäocyten, Trophocyten und Spongioblasten. Beschalte Gemmulae enthalten ausschließlich mit Reservestoffen gefüllte Archäocyten, die vor Fertigstellung der Gemmula-Schale zweikernig werden.Die drei lichtmikroskopisch erkennbaren Schichten der Gemmula-Schale, nämlich die Innen-, die Vakuolen- und die Außenschicht, werden nach einem zur Schwammbasis hin gerichteten Gradienten von einem hochprismatischen Spongioblasten-Epithel sezerniert. Alle Anzeichen sprechen dafür, daß es sich bei diesen Spongioblasten um temporär modifizierte Exopinacocyten handelt.Zu Beginn der Schalenbildung übernimmt ein Verband von flachen Archäocyten an der Peripherie des inneren Zellenkomplexes die Funktion der Formgebung für die entstehende Schale. Diese Zellen sezernieren in Richtung des Spongioblasten-Epithels eine nur elektronenmikroskopisch erkennbare, innere Begrenzungsschicht der Gemmula-Schale.Die in der Gemmula-Schale enthaltenen Mirkroskleren (Amphidisken) werden jeweils in einem Amphidiskoblasten im Mesenchym fertiggestellt und, nachdem Begleitzellen Kontakt zu dem Amphidiskoblasten aufgenommen haben, in das Spongioblasten-Epithel einer Gemmula-Anlage transportiert. Dort wird die Nadel aus dem Zellenkomplex freigesetzt und in die Schale eingebaut.Die Verschlußmembran im Keimporus (Mikropyle) der Gemmula-Schale wird von einer Gruppe modifizierter Spongioblasten (Mikropylen-Spongioblasten) sezerniert. Sie besteht aus der regulären, nur elektronenmikroskopisch erkennbaren, inneren Begrenzungsschicht und zwei weiteren Schichten, die mit keiner Schicht der eigentlichen Gemmula-Schale identisch sind.Die Spongioblasten flachen sich gegen Ende der Schalenbildung zu einem dauerhaften Plattenepithel ab, das auf die Oberfläche der fertigen Gemmula eine dünne Sponginhülle sezerniert.

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Gemmule development in Ephydatia fluviatilis L. (Porifera)

Summary Primordial gemmules in the freshwater sponge Ephydatia fluviatilis consist of archaeocytes, trophocytes, and spongioblasts. Once the shell has been completed the gemmules contain only archaeocytes filled with food reserves; they become binucleate before completion of the shell.The three layers of the gemmule shell discernible in the light microscope — the inner, vacuolar, and outer layers — are secreted by a highly prismatic spongioblast epithelium along a gradient from the apex to the base of the sponge. All the evidence indicates that these spongioblasts are temporarily modified exopinacocytes.Shell formation is initiated when a group of flat archaeocytes at the periphery of the inner cell complex assumes the function of establishing the shape of the shell. That is, they secrete toward the spongioblast epithelium a boundary layer, detectable only electron microscopically, that marks the inner surface of the shell.Each of the microscleres (amphidisks) in the gemmule shell is formed within an amphidiskoblast in the mesenchyme; when auxiliary cells have contacted the amphidiskoblast, they move together to the spongioblast epithelium in a region of the shell. There the spicule is released from the cell complex and incorporated into the shell.The membrane that closes the pore (micropyle) of the gemmule shell is secreted by a group of modified spongioblasts (micropyle spongioblasts). It consists of a continuation of the inner boundary layer lining the shell itself, detectable only electron microscopically, plus two other layers not identical with any layer of the shell.Toward the end of shell formation the spongioblasts flatten, creating a permanent pavement epithelium that secretes a thin envelope of spongin over the surface of the completed gemmule.

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Abkürzungen AC Archäocyte - AD Amphidiske - ADB Amphidiskoblast - AF Achsenfaden - AS Außenschicht der Gemmulaschale - bSpP basale Sponginplatte - BZ Begleitzelle - D Dotterkorn - Di Diktyosom - EnPC Endopinacocyte - ExPC Exopinacocyte - fAC flache Archäocyte - hS homogene Schicht - IS Innenschicht der Gemmulaschale - K Zellkern - KF Kollagenfibrille - KGK Kragengeißelkammer - Kn Kanal - Mi Mitochondrium - MM Mikropylenmembran - MSpB Mikropylenspongioblast - N Nukleolus - Nd Nadel - oS osmiophile Schicht - PE Plattenepithel - rAF radiärer Achsenfaden - rER rauhes endoplasmatisches Reticulum - RVS Randzone der Vakuolenschicht - Sp Spongin - SpB Spongioblast - SpH Sponginhülle - TC Trophocyte - Ves Vesikel - VS Vakuolenschicht - VV Verdauungsvakuole Die Arbeit wurde durch Mittel der Deutschen Forschungsgemeinschaft gefördert. Herrn Professor Dr. N. Weissenfels danke ich für die freundliche Unterstützung und Förderung der Arbeit. Für technische Assistenz danke ich Frau M. Geis, Frau U. Müller, Frau I. Nüssle und Frau B. Zarbock     

An ultrastructural investigation of the hypocerebral organ of the adult Euperipatoides kanangrensis (Onychophora, Peripatopsidae)

The hypocerebral organs of Euperipatoides kanangrensis are a pair of spherical vesicles located ventral to the cerebral ganglia. They develop in the embryo from the most anterior pair of ventral organs, in the antennal segment. The wall of each hypocerebral organ is a dense epithelium of elongate cells with peripheral nuclei. The cytoplasm of the cells includes numerous mitochondria, Golgi bodies and microtubules. The small lumen, located eccentrically within the organ, contains concentrically layered electron-dense material resembling cuticle.Each hypocerebral organ is enclosed by a layer of extracellular matrix continuous with that surrounding the adjacent cerebral ganglion. There are no nerve connections between ganglion and organ, but cellular connections traverse the intervening matrix and could serve as a communication pathway. The ultrastructure of the hypocerebral organs indicates that they are glands.     

Zur Frage der Entstehung der bindegewebigen Strukturen

Ohne ZusammenfassungIm Bereiche des Bindegewebes werden die Zellen und die Zellverbände von den durch das intercelluläre Milieu vermittelten mechanischen Spannungswirkungen orientiert; die gerichteten Zellverbände bestimmen ihrerseits den Verlauf und die Architektonik des Fasergerüstes.     

A pheromonal function for the crural glands of the onychophoran Cephalofovea tomahmontis (Onychophora: Peripatopsidae)

A characteristic feature of onychophorans is the presence of crural glands in males. These exocrine glands open on the ventral surface at the base of the legs. Their restriction to males suggests a sexual function. Histochemical staining of the glands indicates that their secretion has both a lipid and a protein component. Behavioural bioassays show that the secretion acts as a pheromone attractive to conspecific females. The production of a sex pheromone in onychophorans is discussed in relation to their ecology and phylogeny.