The Stylet Apparatus of Monostiliferous Hoplonemerteans

This paper compares the ultrastructure, development, and functionalmorphology of the stylet apparatus in monostiliferous hoplonemerteans(Phylum Nemertea: Class Enopla). The apparatus occurs in themiddle region of the worm's eversible proboscis and consistsof two main components: 1) a central stylet that is attachedto an anchoring device called the basis; and 2) reserve styletsacs that contain nail-like reserve stylets. The knob-shapedproximal piece of the central stylet is embedded in the anteriorend of the basis, and the tapered shaft of the stylet is directedanteriorly. When the proboscis is fully everted, the centralstylet is used to stab such prey as polychaete worms and smallcrustaceans. Wounds inflicted by the stylet allow the introductionof paralytic neurotoxins that are produced by glandular cellsin the epithelial lining of the proboscis. Reservestylets formintracellularly within the reserve stylet sacs and serve toreplace the central stylet when it becomes lost or damaged.Fully developed stylets typically measure 50 to 250 µmin length and comprise an organic core surrounded by an inorganiccortex that contains calcium phosphate. In juvenile worms thatare four days to several weeks old, reserve stylets are assembledbefore other components of the stylet apparatus are fully differentiated.Subsequently, a reserve stylet is transferred to the centralregion of the proboscis and placed on the basis. Stages in theprocess of stylet attachment are described, and the probablesequence by which the stylet apparatus co-evolved with toxin-producingcells is discussed.     

The Morphology of Paranemertes sanjuanensis sp.n. (Nemertea, Monostilifera) from Washington, U.S.A.

The morphology of Paranemertes sanjuanensis sp.n., a new monostiliferous hoplonemertean from San Juan Island, Washington, is described. As in other members of the genus, P. sanjuanensis has numerous eyespots, a proboscis sheath that extends one-half to two-thirds the length of the body, well-developed cephalic and subepidermal glands, and two distinct layers of longitudinal muscles in the body wall of the cerebral region. A precerebral septum is absent, as only fibers from the inner longitudinal layer extend into the proboscis. The cerebral sense organs are well developed and lie just anterior to the brain. The esophagus opens into the rhynchodaeum and leads posteriad, into a highly folded stomach. The intestinal caecum is short and lacks anteriorly directed pouches. Gravid females have numerous ovaries in the posterior two-thirds of their bodies. The proboscis is relatively large and contains an average of 5 reserve stylet sacs, each of which contains 2 to 3 stylets. The stylets are stout and have prominent, helically-arranged grooves.     

Styletogenesis in nemertean worms: The ultrastructure of organelles involved in intracellular calcification

The ultrastructure of cellular organelles involved in stylet formation is examined in six species of nemertean worms by transmission electron microscopy (TEM). Stylets are nail-shaped structures containing calcium phosphate that are assembled intracellularly in large uninucleate cells, called styletocytes. Each stylet develops within a membrane-bound vacuole in the styletocyte cytoplasm. Well developed arrays of Golgi bodies are typically found in the vicinity of developing stylet vacuoles, and fully formed vacuoles are filled with PAS+ material that appears to be derived from the smooth endoplasmic reticulum. At the onset of styletogenesis, a conical sliver of organic material differentiates on the inner surface of the vacuolar membrane. This material displays a species-specific banding pattern in decalcified sections, and apparently acts as a template during calcification of the stylet shaft. After the organic core of the shaft is formed, mitochondria aggregate around the stylet vacuole and presumably help accumulate the calcium used in mineralization of the stylet. A knob-shaped proximal piece is subsequently assembled on the base of the shaft. The proximal piece contains a nonbanded matrix and has electron-dense material at its surface that may help in correctly orienting this region toward the basis during replacement of the central stylet.     

3种蛾类雄性内生殖系统形态学研究

为了探究蛾类昆虫新的有效分类特征,本研究对直脉青尺蛾Geometra valida、白雪灯蛾Chionarctia niveus和多斑豹蠹蛾Zeuzera multistrigata雄性内生殖系统进行了解剖观察和形态学比较。结果表明：3种蛾类雄性内生殖系统均由精巢、贮精囊（前贮精囊和后贮精囊）、输精管、复射精管、单射精管（单射精管原节和单射精管表皮节）和附腺组成;种间形态差异表现在贮精囊的形状及连接方式、复射精管的形状及长短、单射精管和附腺的长度等方面,这些鉴别特征可为蛾类分类及系统发育研究提供形态学借鉴。     

Zur Nahrungsaufnahme vonTetrastemma melanocephalum (Nemertini)

The proboscis of hoplonemerteans is armed with a stylet apparatus, which is used for capturing prey.Tetrastemma melanocephalum (Johnston) is a common hoplonemertean in the littoral of the Baltic Sea and the North Sea. It lives in the phytal and on sand- and mudflats and occurs in large numbers in theCorophium belts in the waddenseas.T. melanocephalum feeds on arthropods, mainly on copepods and amphipods. The prey is caught with the proboscis, penetrated by the stylet and grows weak (reduction of movements) within a few seconds; it is then sucked out. During the summer, a 15–35 mm long nemertean captures about 3 specimens ofCorophium volutator of 3.5–6 mm length per day. In theCorophium belt at Sahlenburg, German Bight, North Sea, 29 nemerteans/0.25m² were found; they feed mainly onC. volutator, so that on average more than 10 000 specimens ofC. volutator/m²/month are sucked out by these nemerteans. Hence,T. melanocephalum is an important consumer ofCorophium.     

An investigation of preferential feeding habit in fourAsclepiadaceae by the Aphid,Aphis nerii B. de F.

Summary Penetration of the stems ofAraujia sericofera, Asclepias curassavica, Cynanchum ellipticum andSarcostemma viminale by stylets of the aphidAphis nerii was studied with light and differential interference contrast microscopes. Of a total of 118 stylets and 446 stylet tracks observed in cross-sections of stems of the fourAsclepiadaceae, 97 stylets and 372 stylet tracks terminated within the internal primary phloem. Of the remainder, 15 stylets and 74 tracks terminated within the external primary phloem. 22 stylets and 179 of the stylet tracks penetrated the external phloem on the way to the internal phloem. Of these, only four stylets and 32 of the stylet tracks showed signs of attempted probes of the external phloem. It is suggested thatAphis nerii may obtain not only its essential food requirements but also cardiac glycosides as a basis for chemical aposematism.     

Asian citrus psyllid stylet morphology and applicability to the model for inter-instar stylet replacement in the potato psyllid

In Hemiptera, presumptive stylets for each consecutive postembryonic instar are manufactured prior to ecdysis to replace the ecdysial stylets discarded with the exuviae. With the discovery that the bacterium “Candidatus” Liberibacter solanacearum accesses the tissues involved in the stylet replacement process of the potato psyllid, a hypothesis was formed that the bacterium could adhere to the stylets of freshly emerged instars and hence gain access to the host plant when feeding is resumed. Although unproven, it was imperative that a model for stylet replacement be built. Stylet morphology and the stylet replacement process of the Asian citrus psyllid (ACP), vector of “C.” L. asiaticus, causal pathogen of citrus greening disease, are comparable to the potato psyllid model system. Morphology consists of a basal terminus with its tab-shaped auricle, a base, shaft, and an apical terminus. Each of the four auricles act as a platform for the replacement apparatus, which is compacted into a tight aggregate of cells, the ‘end-cap’. As modeled, on apolysis of larval instar hypodermis, the aggregate ‘deconstructs’ and expands into a snail shell-shaped tube, the ‘atrium’, that houses the presumptive stylet as it is synthesized. Completed stylets then despool from the atrium and are fitted into their functional positions as the next instar emerges from its exuviae.     

Fine structure of the genital system in the bee parasite,Varroa jacobsoni (Gamasida: Dermanyssina) with remarks on spermiogenesis,spermatozoa and capacitation

The female genital tract ofVarroa jacobsoni is composed of a sperm-access system comprising paired solenostomes located between coxa III and IV, paired tubules, paired rami, an unpaired sperm duct, and an unpaired spermatheca. Another part of the female genital system is confined to egg development and oviposition. It is composed of an ovary (s.str.), in which oocytes mature, and a lyrate organ functioning as a nutrimentary structure. Both compartments, regarded as parts of the gonad, are connected by a region named the camera spermatis. This part is also in continuity with the oviduct I, which is provided with a muscular layer and numerous nerve endings. The following cuticle-lined oviduct II leads to the genital orifice through which the eggs are deposited. The fine structure of all these parts is described. Attention is drawn especially to the peculiar spermatheca which contains the inner cells which are thought to connect by way of free cells with a specialized region of the camera spermatis, thus establishing a cellular bridge through which penetration of capacitated spermatozoa into the ovary s.str. may occur. Lyrate organ and oocytes are connected via intercellular bridges/nutritive cords and are thus comparable to the telotrophic ovarioles of certain insects.The male genital system, composed of unpaired testis, paired vasa deferentia, unpaired accessory gland and ductus ejaculatorius, is described ultrastructurally. Spermiogenesis occurs in cysts and spermatozoa belong to the ribbon type. The vasa deferentia are provided with a muscular layer. For the first time receptors are detected in the proximal part or the ductus ejaculatorius. The accessory gland produces a proteinaceous secretion.Spermatozoa were observed in the female rami and spermatheca. Only in the latter were elongated, capacitated spermatozoa seen.     

Specific criteria in Grania (Oligochaeta,Enchytraeidae)

The structure of the penial bulb and male efferent duct system of Grania species may be used in addition to setal pattern and spermathecal shape to distinguish species. Six penial bulb types are distinguished: (1) a simple, small, glandular bulb surrounding the male pore; (2) a small, glandular bulb, with a large, associated, dorso-medial gland mass; (3) a small glandular bulb, medial to the male pore, with an elongate male bursa (the aglandular sac), the vas deferens exitting directly into the invaginated male pore; (4) a glandular bulb with an aglandular sac and a small, cuticular stylet embedded in the bulb, extending from the ectal end of the vas deferens; (5) a glandular bulb and an aglandular sac with a long stylet extending from the vas deferens, through the bulb into the sac; and (6) glandular bulb reduced or absent, with or without an aglandular sac; with a long stylet and other prominent modifications, usually muscular, of the vas deferens. The details of the male duct structure were consistent within specimens grouped on the basis of setal distribution and shape and detailed spermathecal structure. Diverse male duct patterns are found within the polytypic species G. macrochaeta and G. postclitellochaeta. The positions of the spermathecal and male pores in their respective segments are distinctive for some species.     

Sensory receptors associated with the stylets and cibarium of the rice brown planthopper,Nilapavarta lugens

Summary The stylets of Nilapavarta lugens consist of two maxillae that interlock to form separate food and salivary ducts partially surrounded by two mandibles. The ultrastructure of the sensory innervation of the stylets is described. Each maxilla possesses five neurones which extend to the tip of the stylet. The mandibles also contain five neurones, four of which are paired. The paired neurones comprise a shorter dendrite extending part of the way along the stylet and a longer one extending to the tip. The possible functions of these neurones are discussed. Gustatory receptors are located in the small passageway leading from the food duct to the cibarium. The receptors are in two distinct groups on the epipharyngeal side and one group on the hypopharyngeal side of the food canal. Two to five neurones innervate each receptor which connects to the food canal via a small pore.     

New Dalyelliidae (Platyhelminthes, Rhabditophora) from Buenos Aires Province, Argentina, and their stylet ultrastructure

Two new species of Dalyellidae, Dalyellia callvucurai n. sp. and Gieysztoria namuncurai n. sp., are described from temporary freshwater environments in central Buenos Aires Province, Argentina. The ultrastructure of the stylets of both species is also described. The new species of the genus Dalyellia is the second species of the genus found in the neotropics and the first whose stylet has been studied with scanning electron microscopy. Gieysztoria namuncurai n. sp. joins the seven species of the genus known in Argentina. The ultrastructural characteristics of the stylet place it in the Inaequales group, with complex stylets.     

Anterior alimentary canal of the pear Psylla,Psylla pyricola foerster (Homoptera,Psyllidae)

Scanning and light microscopy investigations of the anterior alimentary canal of the pear psylla, Psylla pyricola Foerster (Homoptera: Psyllidae), revealed the morphology of the labium and stylets, as well as the presence of sensory structures and a valve in the precibarium. The labium consists of three telescoping segments with an internal labial groove, which surrounds and supports the stylet bundle. Also a part of the labial groove is the internal labial clamp. The stylet bundle is comprised of paired styliform mandibles and maxillae, which interlock to form the food and salivary canals. The stylet bundle proximal to the labium forms a large loop within a membranous crumena. When fully retracted the coiled stylets are under tension. Stylet extension generates increasing tension so that when retracted the stylets readily recoil within the crumena. Penetration of leaf tissues by the stylet bundle is dependent on the interaction between stylet muscles, opening and closing of the labial clamp, the barbed stylet tips, and the ventral position of the labium. Proximal to the crumena the paired stylets separate and diverge at the entrance of the precibarium, which is formed by the interlocking of the epi-and hypopharynges. There are 18 sensory structures in the precibarium, as well as a precibarial valve. These structures appear to be homologous to similar structures observed previously in aphids and leafhoppers. The morphology and the location of the precibarial sensilla suggest that, like the precibarial sensory organs of aphids and leafhoppers, they are gustatory and probably mediate acceptance or rejection of plant fluids, thus playing a major role in locating tissues for feeding.     

Ultrastructure of the male reproductive system and spermatophore formation in Labidocera aestiva (Crust.: Copepoda)

Summary The male reproductive system of Labidocera aestiva produces a flask-shaped spermatophore connected to a chitin-like coupling apparatus. As immature spermatozoa leave the anterior region of the testis, they pass through the lumen of a long, sinuous duct composed of a ductus deferens and seminal vesicle. Ultrastructural examination of the ductus deferens reveals a highly glandular, columnar epithelium. The cells contain arrays of rough endoplasmic reticulum and abundant, well-developed Golgi complexes. This region produces and releases into the lumen, a flocculent substance and two granular secretions that constitute the seminal fluid. In its terminal part, the ductus deferens synthesizes another secretion that forms the spermatophore wall enclosing the spermatozoa and seminal fluid. Final synthesis of the spermatophore wall occurs within the thin-walled seminal vesicle, although this region functions primarily as a storage organ. Contiguous to the seminal vesicle is an elongate, highly glandular spermatophore sac. The chitin-like coupling apparatus, which functions to attach the spermatophore to the female, is formed in the anterior region of the sac by secretions from eight cell types. The posterior region of the sac stores the flask-shaped spermatophore and produces secretions that aid ejaculation of the entire spermatophore complex.Contribution No. 236, Harbor Branch Foundation, Inc.     

Sand dwelling Turbellaria from the Netherlands Delta area

Sand dwelling Turbellaria from the Delta of the Rivers Rhine, Meuse and Scheldt have been investigated. Thirty-eight samples taken from littoral and sublittoral stations in the Grevelingen, Eastern and Western Scheldt have been analysed.Thirty-three species were recorded (Acoela were not considered); twenty-four of them are new for the area and seven new species are described.Density and diversity of Turbellaria were higher in the Eastern Scheldt than in the Western Scheldt or in the Lake Grevelingen. A maximum density of 82 ind./100 cm³ was noted. A tentative calculation on relative abundance of the representatives of the different Turbellaria orders is established. Proseriata seem to be dominant in the localities studied.Abbreviations acg : accessory glands - aco : accessory organ - ad : atrial diverticle - b : bursa - br : brain - cil : cilia - cm : circular muscle - cn : cnidosac - co : copulatory organ - cs : cuticular spines - css : cuticular stylet sheat - de : ejaculatory duct - di : ductus intervesicularis - ds : seminal duct - dsp : spermatic duct - en : enteron - fd : female duct - fp : femal pore - ga : genital atrium - gf : glands in female duct - gg : glands - gp : genital pore - hp : adhesive papillae - ivs : intra capsular seminal vesicle - lm : longitudinal muscle - m : mouth - mp : male pore - ov : ovary - p : proboscis - pg : proboscisglands - ph : pharynx - phg : pharyngial glands - r : retractor muscle - rh : rhabdites - rhg : rhabdite glands - rs : seminal receptacle - s : stylet - sta : statocyst - ut : uterus - t : testis - v : vagina - vg : prostate vesicle - vi : vitellary - vs : seminal vesicle     

S.E.M. and polarization microscopy of nemertean stylets

The ultrastructure of the stylets produced by nine species of nemerteans has been examined by scanning electron microscopy (S.E.M.) and polarized light microscopy. Stylets are solid, nail-shaped structures that typically reach lengths of 50–200 μm. Each stylet is composed of a centrally located organic matrix surrounded by an inorganic cortex that contains calcium and phosphorus. When viewed at high magnifications, fine granules can be seen throughout the organic matrix, and the cortex appears to be composed of densely packed homo-geneous material. Fractured specimens and whole matrices isolated from decalcified stylets reveal a close correspondence between the shape of the organic matrix and that of the surrounding cortex. This similarity in morphology suggests that the organic matrix serves as a template during calcification of the stylet. The fact that abundant material can be seen in the core of incinerated stylets, and in the central region of stylets that had been soaked for several hours in sodium hypochlorite, supports the hypothesis that the organic matrix is also highly calcified. Polarization microscopy of nemertean stylets indicates that they are composed of a crystalline, rather than amorphous, form of calcium phosphate. The probable organization of the calcium phosphate crystals is discussed.     

Anatomical correlates of venom production in Conus californicus

Like all members of the genus, Conus californicus has a specialized venom apparatus, including a modified radular tooth, with which it injects paralyzing venom into its prey. In this paper the venom duct and its connection to the pharynx, along with the radular sac and teeth, were examined using light and transmission electron microscopy. The general anatomy of the venom apparatus resembles that in other members of the genus, but several features are described that have not been previously reported for other species. The proximal (posterior) quarter of the venom duct is composed of a complex epithelium that may be specialized for active transport rather than secretion. The distal portion of the duct is composed of a different type of epithelium, suggestive of holocrine secretion, and the cells display prominent intracellular granules of at least two types. Similar granules fill the lumen of the duct. The passageway between the lumen of the venom duct and pharynx is a flattened branching channel that narrows to a width of 10 micro m and is lined by a unique cell type of unknown function. Granular material similar to that in the venom duct was also found in the lumen of individual teeth within the radular sac. Mass spectrometry (MALDI-TOF) demonstrated the presence of putative peptides in material derived from the tooth lumen, and all of the more prominent species were also evident in the anterior venom duct. Radular teeth thus appear to be loaded with peptide toxins while they are still in the radular sac.     

Functional Mouthparts in the Dog Fur Mite Cheyletiella yasguri Smiley, 1965 (Acari,Prostigmata)

The stylet-like chelicerae in C. yasguri are modified claws as they articulate due to muscles in the terminal segment (tarsus) of the modified legs forming the biting apparatus. The united anterior parts of the stylets form a hollow needle through which saliva can be injected 10–20 μm into the skin. When stylets and the salivary duct are retracted they open for ingestion of the dissolved tissue. Thus C. yasguri has external digestion and may leave deposits of saliva in the skin surface of the host. Such deposits probably call for a host reaction—the skin symptoms called cheyletiellosis. Attention is drawn to the striking correspondence between the mouthparts of C. yasguri and those of Tardigrada. They are in principle composed by the same functional elements.     

Ultrastructure of the mouthparts of adult sweetpotato whitefly,Bemisia tabaci Gennadius (Homoptera: Aleyrodidae)

The fine structure of the mouthparts of the whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae), was examined by scanning and transmission electron microscopy. Adult whitefly mouthparts are similar to those of other homopterans, especially aphids, being composed of the labrum, the labium, and the stylets. The stylet bundle is the feeding organ of the whitefly and is composed of 2 mandibular stylets and 2 maxillary stylets. Mandibular stylets, which are located on the outer aspect of the stylet bundle, each contain 2 dendrites. The tips of the mandibular stylets are curved inward, and there are barb-like ridges on the lateral aspects, which probably function in piercing and cutting plant tissues and in anchoring the stylets in the tissues. The maxillary stylets are not innervated and are interlocked to form 2 separate compartments, the food canal and salivary canal. At the distal end of the interlocked maxillary stylets, there is a small depression, which may allow for mixing of the salivary canal and food canal components. Movement of the B. tabaci stylets during feeding is discussed in comparison with other homopterans.     

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.