Redescription of the Chengjiang arthropod Squamacula clypeata Hou and Bergström, from the Lower Cambrian, south-west China

The anatomy of the arthropod Squamacula clypeata Hou and Bergström, 1997 from the Lower Cambrian Chengjiang Lagersta¨tte is redescribed based on four newly excavated specimens. The new material was collected from localities recently discovered in the Kunming area, Yunnan Province, south-west China, and preserves remarkable details of the ventral morphology, revealed by preparation. Squamacula clypeata is dorsoventrally flattened and rounded in outline. The cephalon was covered by a wide, short shield, with a large doublure and a pair of uniramous antennae on the ventral side. The thorax consists of nine somites, each protected by a tergite and carrying at least one pair of biramous limbs. The pygidium is covered with a small rounded tergum. The endopod is segmented, equipped with short spines on the inner margin of the coxa and a claw-like structure distally, and the exopod flap-like, fringed with setae. The limbs in the pygidium are like those in the thorax in shape. Squamacula was most probably a nektobenthic predator. The spinose endopod could walk, grasp and grind. The large flap-like exopod was adapted for swimming and respiration. Its affinities lie with the Arachnomorpha, but the relationships with other known taxa remain ambiguous.     

Salivary glands and salivary pumps in adult Nymphalidae (Lepidoptera)

The salivary glands and salivary pumps were investigated by means of dissection and serial semithin sections in order to expose the anatomy and histology of Nymphalidae in relation to feeding ecology. The paired salivary glands are tubular, they begin in the head, and extend through the thorax into the abdomen. The epithelium is a unicellular layer consisting of a single cell type. Despite the uniform composition, each salivary gland can be divided into five anatomically and histologically distinct regions. The bulbous end region of the gland lies within the abdomen and is composed of highly prismatic glandular cells with large vacuoles in their cell bodies. The tubular secretion region extends into the thorax where it forms large loops running backward and forward. It is composed of glandular cells that lack large vacuoles. The salivary duct lies in the thorax and also shows a looped formation but is composed of flat epithelial cells. The salivary reservoir begins in the prothorax and reaches the head. Its cells are hemispherical and bulge out into the large lumen of the tube. In the head the outlet tube connects the left and right halves of the salivary gland, and its epithelial cells are flat. The salivary pump lies in the head ventral to the sucking pump and leads directly into the food canal of the proboscis. It is not part of the salivary gland but is derived from the salivarium. Both the thin cuticle of the roof of the salivary pump and the thick bottom are ventrally arched. Paired muscles extend from the hypopharyngeal ridges and obviously serve as dilators for the pump. A functional interpretation of the salivary pump suggests that when not in use, the dilators are not contracted and the pump is tightly closed due to its own elasticity. When the dilator muscles repeatedly contract, the saliva is forced forward into the food canal of the proboscis. The salivary gland anatomy was found to be similar to other Lepidoptera. Furthermore, the histology of the salivary glands is identical in all examined butterflies, even in the species which exhibit specialized pollen-feeding behavior.     

Morphology and function of the proboscis in Bombyliidae (Diptera, Brachycera) and implications for proboscis evolution in Brachycera

Based on serial semithin sections and SEM photographs of representatives of European Bombyliinae and Anthracinae, the mouthparts of Bombyliidae are studied and compared with the relevant data from literature on other families of Diptera Brachycera. The three moving units of the proboscis (clypeo-cibarial region, haustellum-maxillary base region, and labella) and their structures and muscles are described. Functions and possible movements are inferred from the structures observed. Articulations both between the parts of the organ and to the head capsule enable the fly to retract its proboscis into a resting position. Proboscis movement from a resting to a feeding position encompasses the following submovements: rotating of the basal clypeo-cibarial region (= fulcrum) against the head capsule, folding of the haustellum-maxillary base region against the fulcrum, evagination and invagination of the labial base, and the labella movements. This is a novelty as compared to the rigid proboscis of Tabanidae and agrees largely with the conditions in the Cyclorrhapha. The evolution of these novelties and their functional significance are discussed. The fulcrum, as well as the haustellum-maxillary base, as the new moving units are deduced from the plesiomorphic state as present in Tabanidae by fusions of sclerites, shifts of musculature and formation of new articulations. Accepted: 5 April 2000     

The functional anatomy and histology of the alimentary canal of the maldanid polychaetes Clymenella torquata and Euclymene oerstedi

The alimentary canal of the maldanid polychaetes Clymenella torquata (Leidy), and Euclymene oerstedi (Claparède (= Caesicirrus neglectus Arwidsson, 1911) resembles, in many ways, that of the arenicolids. It is divided into buccal mass, pharynx, oesophagus, stomach and intestine, the three latter regions showing further subdivision. The buccal mass and anterior pharynx together form an eversible proboscis. The pharynx, oesophagus, and greater part of the intestine are ciliated. Simple feeding experiments, and histochemical tests, suggest that the stomach is concerned with the digestion and absorption of proteins, fats and carbohydrates, that the anterior intestine is a digestive and major absorptive region, and that the posterior intestine is a storage region. Waste materials are stored mainly in the wall of the oesophagus. A certain amount of intracellular digestion is carried out in the intestine of Euclymene but not in Clymenella. The difference is attributed to the richer, diatomaceous diet of Clymenella. British individuals of this species, being apparently selective feeders, differ not only from Euclymene but also from American ones, both of which ingest the substratum non-selectively.
The pharynx, oesophagus and rectum are surrounded by plexuses of blood capillaries, while the remaining regions are associated with a blood sinus system which varies in position and form in the different regions, lying deepest in the absorptive intestine. The gut muscle seems to be more concerned with moving the blood forward through the sinus system and into the anterior plexus than with moving the food backward. One region of the stomach musculature is especially concerned with this circulation. Rectal respiration probably occurs.     

Morphogenesis during asexual reproduction in Pygospio elegans Claparede (Annelida, Polychaeta)

The spionid Pygospio elegans reproduces both asexually and sexually. Using scanning electron and bright field microscopy, we examined morphogenesis following asexual reproduction to determine how "lost" body regions were regenerated after a worm spontaneously divided. Asexual reproduction occurred through transverse fission and divided the parent worm into 2 to 6 fragments (architomy). All fragments retained their original anterior-posterior polarity. Regeneration in all fragments followed a specific series of events: wound healing (day 1); extension of the blastema to generate lost body regions-specifically, the head and thorax for posterior fragments and the tail and pygidium for anterior fragments (days 2-3); segmentation (days 3-6); and differentiation of segment- or region-specific structures (days 4-8). This pattern occurred regardless of where the original division took place. Subsequent growth occurred through addition of terminal setigers anterior to the pygidium followed by differentiation of tail setigers into abdominal setigers, leaving the tail region about 6 to 10 setigers in size. Division rates were compared in worms from three populations in Nova Scotia, Canada. Worms from two populations (Conrad's Beach, Starr's Point) divided more frequently (about 1.2 and 1.3 weeks between divisions, respectively) than worms from Bon Portage Island (3.5 weeks between divisions). Fragments containing the original head (original mouth intact, generally much larger fragment) had a higher survivorship than fragments containing the original tail.     

Morphology of the proboscis of Hubrechtella Juliae (nemertea,pilidiophora): Implications for pilidiophoran monophyly

The proboscis of Hubrechtella juliae was examined using transmission electron microscopy, scanning electron microscopy, and confocal laser scanning microscopy to reveal more features of basal pilidiophoran nemerteans for morphological and phylogenetic analysis. The proboscis glandular epithelium consists of sensory cells and four types of gland cells (granular, bacillary, mucoid, and pseudocnidae‐containing cells) that are not associated with any glandular systems; rod‐shaped pseudocnidae are 15–25 μm in length; the central cilium of the sensory cells is enclosed by two rings of microvilli. The nervous plexus lies in the basal part of glandular epithelium and includes 26–33 (11–12 in juvenile) irregularly anastomosing nerve trunks. The proboscis musculature includes four layers: endothelial circular, inner diagonal, longitudinal, and outer diagonal; inner and outer diagonal muscles consist of noncrossing fibers; in juvenile specimen, the proboscis longitudinal musculature is divided into 7–8 bands. The endothelium consists of apically situated support cells with rudimentary cilia and subapical myocytes. Unique features of Hubrechtella's proboscis include: acentric filaments of the pseudocnidae; absence of tonofilament‐containing support cells; two rings of microvilli around the central cilium of sensory cells; the occurrence of subendothelial diagonal muscles and the lack of an outer diagonal musculature (both states were known only in Baseodiscus species). The significance of these characters for nemertean taxonomy and phylogeny is discussed. The proboscis musculature in H. juliae and most heteronemerteans is bilaterally arranged, which can be considered a possible synapomorphy of Hubrechtellidae + Heteronemertea (= Pilidiophora). J. Morphol. 274:1397–1414, 2013. © 2013 Wiley Periodicals, Inc.     

Evolution of the suctorial proboscis in pollen wasps (Masarinae, Vespidae)

The morphology and functional anatomy of the mouthparts of pollen wasps (Masarinae, Hymenoptera) are examined by dissection, light microscopy and scanning electron microscopy, supplemented by field observations of flower visiting behavior. This paper focuses on the evolution of the long suctorial proboscis in pollen wasps, which is formed by the glossa, in context with nectar feeding from narrow and deep corolla of flowers. Morphological innovations are described for flower visiting insects, in particular for Masarinae, that are crucial for the production of a long proboscis such as the formation of a closed, air-tight food tube, specializations in the apical intake region, modification of the basal articulation of the glossa, and novel means of retraction, extension and storage of the elongated parts. A cladistic analysis provides a framework to reconstruct the general pathways of proboscis evolution in pollen wasps. The elongation of the proboscis in context with nectar and pollen feeding is discussed for aculeate Hymenoptera.     

Biostratinomy and functional morphology of enrollment in two Middle Devonian trilobites

Although it is common knowledge that many trilobites enrolled, behavioral and functional aspects of enrollment are not at all well understood. Taphonomic details portrayed by enrolled trilobites in the Middle Devonian Hamilton Group (New York State) indicate that enrollment was a complex and morphologically constrained behavior. The trilobites Phacops rana (Green) and Greenops boothi (Green) are frequently enrolled in Hamilton strata; biostratinomic data indicate two very different enrollment postures. Interlocking morphologies (coaptative devices) and apodeme structure and disposition indicate that these postures reflect specific behaviors which involved interaction between tergal structures, inferred musculature, and the substratum. Phacops enrolled by burrowing forward and down into the sediment; dorsal muscles, attached to prominent articulating half-rings, imbricated the thorax such that each lappet overlapped the next posterior segment and locked into a posterior pleural facet. The pygidium was brought into place as the posterior segments of the thorax were placed into vincular notches along the lateral margin of the ventral cephalon. The pygidium locked with the cephalic vincular furrow to complete ‘perfect sphaeroidal’ closure. Greenops enrolled with the cephalon in an upright position at the sediment surface; a submarginal furrow on the ventral surface of the pygidium received the anterior rim of the cephalon. Relatively narrow articulating half-rings limited pleural rotation. Segments were loosely locked into narrow facets at the anterior margin of the next posterior lappet. In spite of rudimentary lappet and half-ring structures, Greenops displays an elaborate system of thoracopygidial muscles which involved dorsoventral and longitudinal attachments along the thorax and into the pygidium. Phacops, in contrast, displays very poorly developed apodemes which occur in the thorax only. Longitudinal muscle strength was likely less important during Phacops enrollment than is evident for the Greenops enrollment procedure. Conversely, Phacops clearly relied to a great degree upon competent closure devices which are poorly developed in Greenops. Biostratinomic data reveal different enrollment behaviors which reflect the function of different enrollment-related morphologies present in each species.     

Groundplan Anatomy of the Proboscis of Butterflies (Papilionoidea, Lepidoptera)

The anatomy of the proboscis was studied in representatives of all major subfamilies of Papilionoidea and several outgroup taxa which included Hesperiidae, Hedylidae and Geometroidea. In all species the cross-sectional outline of the tapering proboscis continuously changes from proximal to the tip while the central food canal, formed by the concave medial galeal walls, retains its oval shape. Each galea contains three types of muscles, a branching trachea, nerves, sensilla, and at least one longitudinal septum. We focused on the varying arrangement and distribution of the intrinsic galeal muscles from the basal galeal joint to the tip region. The plesiomorphic condition of the galeal composition of Papilionoidea is regarded to include one basal intrinsic muscle in the basal joint region and two series of intrinsic muscles, i.e. the lateral intrinsic galeal muscles and the median intrinsic galeal muscles, both series extending from the proximal region to the tip region. The plesiomorphic arrangements of the intrinsic muscle series are found in all representatives of Papilionidae, in one species of Lycaenidae (sensu lato), in many Nymphalidae (sensu lato), and in all outgroup species. Three apomorphic character states are distinguished regarding the presence and extension of the median intrinsic galeal muscles. (1) Present up to 35% of the proboscis length and absent distally in Pieridae, Lycaeninae (Lycaenidae), Satyrinae (Nymphalidae), and Danainae (Nymphalidae). (2) Present in the proximal third of the proboscis and again near the tip between 80 and 90% of the proboscis length in the examined Heliconiinae (Nymphalidae). (3) Completely absent, as in one lycaenid species from the subfamily Riodininae.     

Morphological and molecular data argue for the labrum being non-apical, articulated, and the appendage of the intercalary segment in the locust

Our analysis of head segmentation in the locust embryo reveals that the labrum is not apical as often interpreted but constitutes the topologically fused appendicular pair of appendages of the third head metamere. Using molecular, immunocytochemical and retrograde axonal staining methods we show that this metamere, the intercalary segment, is innervated by the third brain neuromere-the tritocerebrum. Evidence for the appendicular nature of the labrum is firstly, the presence of an engrailed stripe within its posterior epithelium as is typical of all appendages in the early embryo. Secondly, the labrum is innervated by a segmental nerve originating from the third brain neuromere (the tritocerebrum). Immunocytochemical staining with Lazarillo and horseradish peroxidase antibodies reveal that sensory neurons on the labrum contribute to the segmental (tritocerebral) nerve via the labral nerve in the same way as for the appendages immediately anterior (antenna) and posterior (mandible) on the head. All but one of the adult and embryonic motoneurons innervating the muscles of the labrum have their cell bodies and dendrites located completely within the tritocerebral neuromere and putatively derive from engrailed expressing tritocerebral neuroblasts. Molecular evidence (repo) suggests the labrum is not only appendicular but also articulated, comprising two jointed elements homologous to the coxa and trochanter of the leg.     

The röle of the head coelom in proboscis eversion in Arenicola marina (I.)

The dependence of proboscis eversion on the behaviour of the trunk coelom and the effect of increasing the external resistance to eversion have been investigated in Arenicola marina (L.).Two types of proboscis eversion are distinguished; Type I, in which there is an increase of 50–100% in the volume of the head region and where the high pressures recorded in the trunk coelom are needed, it is suggested, to force fluid into the head coelom; Type II, in which the volume change in the head region is small and where simultaneous recordings of head and trunk coelomic pressures indicate that the head coelom can be isolated from the rest of the coelom.Pressures in the trunk are only related to the extent of proboscis eversion when there is a high external resistance to eversion.     

The functional morphology of feeding in three species of maldanid polychaetes

The functional morphology of deposit feeding relative to proboscideal morphology of the maldanid polychaetes Axiothella rubrocincta (Johnson, 1901), Clymenella californica Blake & Kudenov, 1974, and Praxillella affinis pacifica (Berkeley, 1929) from central California is presented. The proboscides of these species are externally and internally similar. They consist of a cuticulatized buccal mass, a bucco-pharyngeal junction and ciliated pharynx. A functional unit of the feeding process is the palpode because its secretions enable the proboscis to be effectively everted. These worms exploit die physical properties of the substratum by changing its dilatancy (and thixotropy) while feeding. The rapidly emerging buccal mass increases the dilatancy of the sediment and provides a penetration anchor. The buccal mass partially deflates and loosens the substratum just prior to the forceful extrusion of the bucco-pharyngeal junction. Sediment about the latter region becomes dilatant. The proboscis then shortens and widens, causing the substratum about the pharynx to become thixotropic while it becomes dilatant about the region of the proboscis proximal to the pharynx. The worms push their proboscides into the loosened sediment while pharyngeal ciliary currents and the undulating bucco-pharyngeal margin draw food into the pharynx. Pharyngeal cilia and the buccal mass function in particle selection.
The maldanids and arenicolids examined to date share similar and basic proboscideal morphologies and activities. It is suggested that the feeding mechanism described for the maldanids, A. rubrocincta, C. californica and P. affinis pacifica , will be found in some members of both families.     

Functional morphology of the feeding apparatus and evolution of proboscis length in metalmark butterflies (Lepidoptera: Riodinidae)

An assessment of the anatomical costs of extremely long proboscid mouthparts can contribute to the understanding of the evolution of form and function in the context of insect feeding behaviour. An integrative analysis of expenses relating to an exceptionally long proboscis in butterflies includes all organs involved in fluid feeding, such as the proboscis plus its musculature, sensilla, and food canal, as well as organs for proboscis movements and the suction pump for fluid uptake. In the present study, we report a morphometric comparison of derived long‐tongued (proboscis approximately twice as long as the body) and short‐tongued Riodinidae (proboscis half as long as the body), which reveals the non‐linear scaling relationships of an extremely long proboscis. We found no elongation of the tip region, low numbers of proboscis sensilla, short sensilla styloconica, and no increase of galeal musculature in relation to galeal volume, but a larger food canal, as well as larger head musculature in relation to the head capsule. The results indicate the relatively low extra expense on the proboscis musculature and sensilla equipment but significant anatomical costs, such as reinforced haemolymph and suction pump musculature, as well as thick cuticular proboscis walls, which are functionally related to feeding performance in species possessing an extremely long proboscis. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2013, 110 , 291–304.     

THE EXTRAORDINARY TRILOBITE FENESTRASPIS (DALMANITIDAE, SYNPHORIINAE) FROM THE LOWER DEVONIAN OF BOLIVIA

Abstract:  The hitherto poorly known, monotypic trilobite genus Fenestraspis from the Lower Devonian of Bolivia is revised and its original assignment to the Synphoriinae supported. The thoracic morphology of the genus remains very poorly known. Fenestraspis is morphologically unusual because of the development of extensive fenestrae in the pleural region of the pygidium and apparently of the thorax; the presence of upwardly directed spines on the cephalon, thorax and pygidium; and the exceptionally large and highly elevated eyes with the palpebral rim projecting outwards above the visual surface. The function of the fenestrae remains uncertain. If they formed openings in the body of the trilobite in life they may have allowed circulation of oxygenated water to the limb exites so that respiration could have been maintained while the trilobite was enrolled. If they were covered with a flexible membrane, they may have been secondary respiratory structures or had a sensory function. The Synphoriinae is regarded as a subfamily of the Dalmanitidae rather than as an independent family of the Dalmanitoidea as proposed by some authors. The type species of the poorly known monotypic genus Dalmanitoides from the Lower Devonian of Argentina is illustrated photographically for the first time and compared with Fenestraspis .     

Distribution of Ultrabithorax proteins in Drosophila

We have used a monoclonal antibody to examine the distribution of Ultrabithorax (Ubx) proteins in Drosophila embryos and imaginal discs by immunofluorescence. Ubx proteins are nuclear and show a spatially restricted distribution in the nervous system, epidermis and mesoderm. Labelling extends from the first thoracic segment (T1) to the eighth abdominal segment (A8) in the midline cells, from T2 to A8 in the ventral nervous system and epidermis and from A1 to A8 in the somatic mesoderm. In the nervous systems and epidermis the patterns of labelling exhibit a repeat unit, the Ubx metamere, that is out of phase with the segmental repeat unit. At least in the epidermis this repeat unit appears to extend between anterior-posterior compartment boundaries and consists of a posterior compartment together with the succeeding anterior compartment. The most prominently labelled metamere in the nervous system and epidermis is that comprising the posterior region of T3 and the anterior region of A1. Within each metamere the nuclei are heterogeneously labelled. Clear heterogeneity of labelling is also seen amongst the nuclei of the T3 imaginal discs.     

The metatrochophore of a deep-sea hydrothermal vent vestimentiferan (Polychaeta: Siboglinidae)

Vestimentiferans (Siboglinidae, Polychaeta) live as juveniles and adults in an obligate mutualistic association with thiotrophic bacteria. Since their development is aposymbiotic, metatrochophores of vestimentiferans from the East Pacific Rise colonizing deep-sea hydrothermal vents are infected with the specific symbiont, develop the trophosome, and reduce their digestive system. To gain insight into the anatomy and ultrastructure and to compare this stage with metatrochophores from other siboglinids, we serial sectioned and reconstructed three specimens using light and transmission electron microscopy. The metatrochophore was composed of a prostomium, a small peristomium, two chaetigers (or two chaetigers and one additional segment without chaetae), and a minute pygidium. A digestive system and an intraepidermal nervous system were developed. Larval organs such as the prototroch, the neurotroch, and an apical organ were present, along with juvenile/adult organs such as tentacles, uncini, pyriform glands, and the anlage of the nephridial organ. We propose that in vestimentiferans, the vestimentum is the head arising from the prostomium, peristomium, and the anterior part of the first chaetiger. In frenulates, in contrast, the head is composed on the one hand of the cephalic lobe arising from the prostomium and on the other of the forepart developing from the peristomium and the anterior part of the first chaetiger. In frenulates the muscular septum between the forepart and trunk develops later than the first two chaetigers. Since this septum has no counterpart in vestimentiferans, the forepart-trunk border of frenulates is not considered homologous with the vestimentum-trunk border in vestimentiferans. The obturacular region in vestimentiferans does not appear to be a body region but rather the head appendages arising from the first chaetiger. In contrast, the tentacles in frenulates are prostomial head appendages. In both taxa, the trunk is the posterior part of the first chaetiger, and the opisthosoma is the following chaetigers and the pygidium. Comparisons with other polychaetes suggest that two larval segments are autapomorphic for the monophyletic Siboglinidae.