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.     

Ultrastructural study of the proboscis endothelium of Riseriellus occultus (Nemertea, Heteronemertea)

We have examined with transmission electron microscopythe epithelial layer exposed to the rhynchocoel fluidof the proboscis in the heteronemertine Riseriellus occultus. This epithelium is organized asa monociliated, pseudostratified myoepitheliumconsisting of two cell types: apically situatedmonociliated supportive cells and subapical myocyteslacking cilia. The low supportive cells form acontinuous adluminal sheet and reach with numerouscytoplasmic processes into the extracellular matrix;these cells are characterized by numerous, irregularlyshaped, apical folds projecting into the rhynchocoelfluid, delimiting broad extracellular spaces. Theauthors suppose that both apical and basal folds couldaccommodate stretching of the endothelium when theproboscis is everted. The apical folds of thesupportive cells increase the interface of these withthe rhynchocoel fluid; this feature, together with thepresence of pinocytotic vesicles in such cells,suggest that they could be involved in the exchange ofsubstances between the rhynchocoel fluid and theproboscis. The myocytes are scattered singly withinthe monociliated pseudostratified myoepithelium. Theyare situated between the supportive cells and thesubjacent extracellular matrix. Basement membraneseparating both cells types is lacking. Myofibrillarparts protrude basally from the myocyte somata. Themyofibrillar parts lie in direct apposition to theextracellular matrix, and are oriented circular to thelongitudinal axis of the proboscis. We consider themyocytes to be intra-epithelial, myoepithelial cells.     

Proboscis musculature in the butterfly Vanessa cardui (Nymphalidae, Lepidoptera): settling the proboscis recoiling controversy

Krenn, H. W. 2000. Proboscis musculature in the butterfly Vanessa cardui (Nymphalidae, Lepidoptera): settling the proboscis recoiling controversy. —Acta Zoologica (Stockholm) 81 : 259–266 The proboscis of Vanessa cardui (Nymphalidae) contains two basal galeal muscles and two different series of numerous oblique muscles. Both muscle series extend from the proximal region up to the tip‐region; the individual muscles of each series run a constant course throughout the proboscis. In contrast to other butterflies, the knee bend region does not have additional types of muscles. The analysis of shock‐frozen proboscises reveals that the dorsal wall is arched outwardly in the uncoiled, feeding position whereas in the coiled, resting position the dorsal proboscis wall is flat or concave. This results in a significantly greater cross‐sectional area due to the significantly greater dorso‐ventral diameter in uncoiled proboscises. After freezing the proboscis in its distal region, it can still be uncoiled, however, it cannot be fully recoiled. These morphometric and experimental results indicate that the oblique proboscis muscles are responsible for recoiling the proboscis to the resting position.     

Anatomy and ultrastructure of the proboscis in Mesorhynchus terminostylis (Platyhelminthes,Rhabdocoela)

The ultrastructural organization of the proboscis in Mesorhynchus terminostylis is distinctly different from that in other members of the Polycystididae in which it is currently classified. The sheath epithelium is formed by three belts, all with intra-epithelial nuclei. The apical belt of the bipartite cone epithelium has a single intrabulbar nucleus, and the basal belt possesses five insunk nucleiferous cell parts behind the bulb. Six types of glands surface through the epithelia; the three types emerging through the cone epithelium can be homologized with those described for Polycistis naegelii. Only uniciliary receptors are found in the epithelium. The musculature in the bulb has a very loose appearance, and the bulbar septum appears to be a bipartite basement membrane. The septum can be considered the basement membrane of the cone epithelium as if the contractile portion of the inner longitudinal muscles have invaded the epithelium and come to lie between the epithelial cells and the basement membrane. Thus the inner musculature of the bulb is entirely intraepithelial as is the case for Psammorhynchus tubulipenis and Cytocystis clitellatus. The systematic position of M. terminostylisremains uncertain but seems to lie between Psammorhynchus and Cytocystis on one hand and Koinocystididae and Polycystididae on the other.     

Microscopic anatomy of the integument in the ribbon worm Micrura bella (Stimpson, 1857) (Pilidiophora,Nemertea)

The integument of ribbon worms in the order Heteronemertea is distinct from the integuments in the other taxa of nemerteans due to the presence of a special subepidermal glandular layer, the cutis. Among heteronemerteans, the ultrastructure of the cutis has been studied only in the Lineus ruber species complex. In the current study, ultrastructural (transmission electron microscopy) and histochemical studies of the epidermis and the cutis of Micrura bella from the basal Lineage A of the family Lineidae were performed. The epidermis consisted of ciliated and serous gland cells and is separated from the cutis by a layer of the subepidermal extracellular matrix; the basal lamina was not detected. The cutis comprised musculature, two types of mucous and four types of granular gland cells, and pigment cells with four types of granules. In the cutis of juvenile worms, type II granular gland cells and type II mucous cells were not observed. The integument of the caudal cirrus consisted of ciliated and serous gland cells and two intraepidermal lateral nerve cords; the cutis was absent. The compositions of the integument glands of M. bella and the L. ruber species complex are similar, except for the presence of type IV granular gland cells with narrow rod-shaped and lamellated granules exhibiting an alternating dark and light transverse layers and type II mucous cells found only in M. bella.     

Functional morphology and movements of the proboscis of Lepidoptera (Insecta)

Summary The mouthparts of Lepidoptera were investigated in a number of species by morphological and cinematographical methods. Both the galeae (which compose the proboscis) and the basal maxillary components (stipites) were studied in the resting position, in motion, and during feeding. In the resting position the proboscis is coiled so tightly that the surfaces of the consecutive coils are in close contact and the outermost coil touches the ventral side of the head. Cuticular processes of the galeal wall interlock between the coils in this position. In the investigated species they occur on the galeal wall and on the ventral side of the head in varying number and distribution. By the extension of the basal galeal joint, the coiled proboscis is released from its resting position and is elevated continuously. It uncoils in 3–5 steps which effect the entire length simultaneously. Each uncoiling step occurs synchronously with a compression of the stipital tubes on either side of the body. These compression movements pump hemolymph into the galeae. In all investigated Lepidoptera the uncoiled proboscis shows a distinct downward bend at a certain point which is also detectable in anaesthetized or freshly killed animals in some species. This feeding position and the movements of the uncoiled proboscis are similar in all species despite the intrinsic galeal muscles being variously arranged in the galeal lumen in different Lepidoptera. When comparing cross-sections through corresponding regions of coiled and uncoiled proboscises, the curvatures of the dorsal galeal walls remain unchanged. Coiling of the proboscis starts at the tip and progresses to the base. After coiling the proboscis tightly beneath the head, the diameter of the spiral widens due to its elastic properties until the proboscis props itself against the ventral side of the head. This elastic effect combined with the interlocking cuticular processes seems to be responsible for the resting position of the proboscis.Abbreviations an antenna - bre bend region - ca cardo - ci cibarium - cl clypeus - co complex eye - cp cuticular process - dre distal region - esm external tentoriostipital muscle - fc food canal - fst flat part of the stipes - ga galea - hs horizontal septum - igm intrinsic galeal muscles - ism internal tentoriostipital muscle - la labium - lap labial palpus - lr labrum - mxp maxillary palpus - ne nerve - pi pilifer - pom primary oblique galeal muscles - pr proboscis - pre proximal region - sa salivarium - se sensillum - som secondary oblique galeal muscles - st stipes - stl stipital lamella - te tentorium - tr trachea - tst tubular part of the stipes - vm ventral membrane - vs vertical septum     

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.     

Ultrastructure of the subepidermal musculature of Xenoturbella bocki, the adelphotaxon of the Bilateria

 Xenoturbella bocki is the only species of the high-ranked taxon Xenoturbellida. The species lives on marine mud bottoms at a depth of 20–120 m and moves extremely slowly by ciliary gliding. Nevertheless it possesses a well-developed body wall musculature with outer circular muscles, a prominent layer of inner longitudinal muscles and radial muscles that extend from the outer circular myocytes to the musculature surrounding the gastrodermis. The longitudinal myocytes are not compact cells, but form fascicles of fibrils running parallel to each other. Fine cytoplasmic cords connect the fibres of a cell to each other and with its nuclear region. The muscles are embedded within a sometimes expansive extracellular matrix (ECM) that lacks any fibrillar components. All muscle cells display conspicuous and numerous cytoplasmic extensions that are intermingled with each other. Tight coupling between adjacent cell membranes is not found, but zonula adhaerens-like junctions exist. Fibrils belonging to different myocytes, but also fibrils of the same cell, are coupled by such cytoplasmic extensions. Circular, radial and at least the peripheral longitudinal myocytes display cell-matrix connections with the internal lamina, a component of the subepidermal ECM. This internal lamina projects down into the centres of the fascicles with longitudinal muscle fibrils and forms extensive attachment zones with the muscle cells, reminiscent of focal contacts. For the ingestion of food, X. bocki opens the simple mouth pore and protrudes the aciliated gastrodermis. The body wall musculature is responsible for this protrusion and also for the withdrawal of the gastrodermis. In the past, possible phylogenetic kinships with the Acoelomorpha (Plathelminthes) or the Enteropneusta and Holothuroidea were discussed, but, on the basis of all information available, X. bocki is hypothesized to be the sister taxon of the Bilateria. Accepted: 2 April 1997     

Organisation of the praesoma in Acanthocephalus anguillae (Acanthocephala, Palaeacanthocephala) with special reference to the muscular system

The organisation of the praesoma in the parasite Acanthocephalus anguillae was studied on the light and electron microscopic level, with emphasis on the morphology of the musculature. The study was compiled to add new data to the ground pattern of the Acanthocephala for analysis of the phylogenetic relationships within the Gnathifera. In A. anguillae the praesomal epidermis and lemnisci form a coherent syncytium, separated from the epidermis of the trunk. Hooks are seen to be derivatives of the subepidermal basal lamina and are covered by the praesomal epidermis. The praesomal circular body wall musculature forms a network of anastomosing muscle fibres that lines the proboscis; a praesomal longitudinal body wall musculature does not exist. The truncal circular and longitudinal body wall musculature rise up to the praesomal proboscis. The unpaired proboscis retractor, consisting of longitudinal circomyar fibres, forms an outer and an inner concentric tube; the latter extends through the entire praesoma and penetrates the receptacle wall. The sack-like receptacle is surrounded by a receptacle constrictor. The nervous system of the praesoma consists of a prominent cerebral ganglion, three nerves which extend anteriorly, ramify and end within the praesomal musculature, and two strong lateral posterior nerves. A. anguillae lacks an apical organ, lateral organs and a support cell. Many of the features present in the praesoma of A. anguillae can be assumed as ground-pattern characteristics of the Acanthocephala. Accepted: 22 January 2001     

The Ultrastructure of the Proboscis in Psammorhynchus tubulipenis Karling, 1964 and Cytocystis clitellatus Karling, 1953 (Platyhelminthes,Rhabdocoela)

The ultrastructural organization of the proboscis in two species of free-living Platyhelminthes, Psammorhynchus tubulipenis and Cytocystis clitellatus is very alike but differs from previously described species. Both sheath and cone epithelium are composed of two circumferential belts. Only the basal cone epithelium is syncytial, while no nuclei were found in the distal belt of the sheath epithelium. The sheath epithelium is characterized by numerous infoldings of the basal plasma membrane. The nuclei present in the bulb belong to the proximal belt of the sheath epithelium and the apical cone epithelium. Nuclei of the basal cone epithelium are located insunk behind the proboscis bulb. The insunk cell parts pierce the septum of the bulb laterally near the proximal end. Different types of gland necks and sensory cells pierce the epithelia. Associated with the distal belt of the sheath epithelium, two sensory organs are found, containing multiciliary receptors with modified axonemata. Differences in organization of the proboscis musculature are described and compared with the organization in other species. The systematic position of both species is discussed in the light of the new findings.     

Ultrastructural Observations on the Dwarf Male of Bonellia viridis (Echiura)

The organization of the dwarf male of Bonellia viridis was studied by electron microscopy. The epidermis is formed by two types of epithelial cells: the majority are multiciliated cells; highly vacuolated, non-ciliated cells are less abundant. The body wall musculature consists of an outer circular, a diagonal, and a longitudinal layer. As a unique feature in coelomate spiralians it was found that the perikarya of all muscle cells are located internal to the entire contractile muscular layer. The muscles are solitary myocytes embedded in extracellular matrix. Masses of secretory and indifferent cells occur inside the muscles. Two types of secretory cells were distinguished. Both of them apparently undergo holocrine secretion. A complete lining of thin peritoneal cells delimits the body cavity. Also, the gut and sperm sac have a complete peritoneal lining. The coelomic lining of the gut is a single-layered myoepithelium, that of the sperm sac a pseudo-stratified myoepithelium. The vas deferens was seen to be ciliated. The entrance of the sperm sac is formed by a ciliated funnel that leads into the reservoir by means of a thin, ciliated canal. The existence of repeated transverse nerves and of four longitudinal nerve cords is described for the first time.     

Organization and differentiation of the body-wall musculature in Macrostomum (Turbellaria,Macrostomidae)

We studied the body-wall musculature, its ECM (extracellular matrix), and the junctional complexes between muscle cells and between muscle cells and ECM in Macrostomum hystricinum marinum Rieger, 1977, using Nomarski-contrast and electron microscopy. Differentiation of these body-wall components was followed by monitoring embryonic stages at 52%, 64%, and 82% of the time between egg-laying and hatching and with study of the hatchling and adult stages. For comparison, the body-wall musculature of other macrostomidans has been examined in conventional light-histological sections.Muscles form a grid of longitudinally, diagonally, and circularly oriented fibers beneath the epidermis in M. hystricinum marinum and this orientation of cells can be found already in embryos at 64% development. Younger embryos at 52% development show no muscle differentiation. The ECM forms a net-like arrangement that apparently envelops the individual muscle cells. Characteristic knob-like thickenings of the ECM occur at the base of the epidermis. Muscle cells attach to each other, to the epidermis, and to other cell types through hemidesmosome-like junctions at thickenings of the ECM in the adult and hatchling stages; no true desmosomes exist between muscle cells. Gap junctions occur commonly between longitudinal muscles of adult specimens and between perikarya of muscle cells in embryos at 64% and 82% development.More comparative studies are needed to determine the systematic value of presence or absence of the diagonal muscle fibers in the body wall of turbellarians.     

Functional morphology of musculature in the acoelomate worm, Convoluta pulchra (Plathelminthes)

Convoluta pulchra is a small worm living in the surface sediment of mud flats where it feeds on diatoms. It is roughly teardrop in shape with a ventral groove in which the mouth sits, and it can move in a variety of ways, readily distorting its body in bending, twisting, and turning motions. Fluorescently labeled probes for filamentous actin revealed the musculature in whole mounts of the worm. In the body wall, the musculature consisted of a grid of circular, longitudinal crossover (that is, with a longitudinal orientation in the anterior half of the body but arcing medially to cross over to the contralateral side of the body behind the level of the mouth), and a few diagonal fibers. Inside the body was a strong, irregular brush of muscles originating at the rostral tip of the body and anchoring laterally and posteriorly along the body wall, and strong dorsoventral muscles flanked the ventral groove. Two fans of muscles in the ventral and dorsal body wall reached posteriorly and laterally; that on the dorsal side originated at junctures of the dorsoventral muscles with the body wall and that on the ventral body wall originated from the mouth. By their positions, certain groups of muscles could be correlated with given movements: the crossover muscles with some turning motions and feeding, and the inner muscles with probing and retraction motions of the rostrum and with a tuck-and-turn motion the worm used to turn itself around. Electron microscopy showed numerous maculae adherentes junctions linking all muscle types and special junctions linking the musculature with the epidermis. The latter myoepidermal junctions were of dimensions larger than those of maculae adherentes and contained an interlaminar material which we believe represents islands of basal matrix comparable to basement membrane. Accepted: 12 July 1999     

An enigmatic heteronemertean from the Gulf of Mexico

Heteroenopleus enigmaticus gen. nov., sp. nov. isdescribed from the northwestern Gulf of Mexico. Itoccurs both in the nearshore Gulf and in high salinityestuarine areas. Body wall musculature conforms tothe general plan of heteronemerteans, i.e. outerlongitudinal, middle circular and inner longitudinalmuscle layers. The head bears a pair of horizontallateral slits, characteristic of the lineids. Theproboscis musculature is of the heteronemerteanpalaeotype with two muscle layers, outer circularand inner longitudinal. Other morphologicalcharacters agree with those of heteronemerteans withone major exception: the proboscis is armed with tworows of structures, herein named parastylets. Thisarmature has no morphological similarity to either themicrovillar proboscideal spines of heteronemerteans orto the stylets of mono- or polystiliferans. A newsubfamily Heteroenopleinae is erected to contain theapomorphic character of an armed proboscis.     

Neuromuscular control systems in the proboscis of Paranemertes peregrina

Neural systems underlying muscular control in the proboscis of Paranemertes peregrina were investigated through the effects of various neuropharmacological agents on electrical and contractile activity.

Peristalsis in the circular muscle was elicited by catecholaminergic drugs. Each wave was accompanied by a spindle‐shaped burst of electrical activity. The occurrence and rate of peristalsis could be manipulated separately, suggesting the presence of a polyneuronal pathway. Acetylcholine elicited contraction of the longitudinal musculature, with little or no obvious accompanying electrical activity. The circular and longitudinal control systems exhibited reciprocal inhibition, which appeared to occur prior to the postsynaptic neuromuscular junction. Additionally, both systems were excited by serotonin.

Histochemical localisations revealed cholinesterases in the longitudinal musculature. Norepinephrine in the proboscideal nerve cords and serotin in the proboscideal nerve cords and plexus were demonstrated through fluorescence spectrophotometry.     

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     

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.     

The ovipositor musculature of Bactrocera depressa Shiraki (Diptera, Tephritidae)

Structure of the ovipositor sclerites and musculature was studied in the tephritid fly Bactrocera depressa Shiraki, whose larvae develop in the fruits of Cucurbita moschata and other Cucurbitaceae. The functioning and adaptations of the ovipositor of this species to laying eggs into soft fruits are discussed with respect to their differences from the ovipositor characteristics in species with different host specializations, e.g., Ceratitis capitata (Wiedemann) (Hanna, 1938), Lenitovena trigona Matsumura (Ovtshinnikova, 2008), Urophora affinis Frauenfeld and U. quadrifasciata (Meigen) (Berube and Zacharuk, 1983) and Campiglossa plantaginis (Haliday, 1833) (Ovtshinnikova, 2010). The ovipositor musculature of Bactrocera depressa is very similar to that of Ceratitis capitata, a species which lays eggs in soft tissues of various fruits. The sclerites and musculature of the ovipositor, especially the basal part of syntergosternite VII, in the fruit infesting Bactrocera (also in Ceratitis) is intermediate between that in Lenitovena laying eggs in the (soft) decaying wood, and Urophora and Campiglossa that deposit eggs in the hard flowerheads of asteraceans. Species of the latter genera have still more complicated structure of the basal part of syntergosternite VII enabling a more intense protruding of the ovipositor and its more closely controlled operating during oviposition in the harder plant tissues. The discussed morpho-functional rearrangements proceed within species of a single lineage of the modern classification (Korneyev, 1999) from the basal Lenitovena to the terminal Urophora and Campiglossa, Bactrocera occupying an intermediate position in this row. In this way, the technology changes (from a muscul lever to a pump) resulting in an increase of the ovipositor mobility during piercing of the substrate.