Redescription of Ektaphelenchoides compsi Baujard, 1984 (Tylenchina: Aphelenchoididae) isolated from Pinus massoniana in Fujian Province, China

Summary Ektaphelenchoides compsi is redescribed morphologically with new molecular characterisation. It was isolated from a dead Pinus massoniana tree in Ningde City, Fujian Province, China. Detailed morphology of the spicule, female gonad, hemizonid position, arrangement of male caudal papillae and female tail terminus shape are documented. It is characterised by a lateral field with three lines (forming two bands), tripartite stylet 17.8 (17.0-19.4) μm long without basal thickenings, metacorpus rectangular with anterior 40% granular and posterior part weakly muscular, metacorpal valve slightly posterior to middle of metacorpus, excretory pore at level of nerve ring, vagina with thickened walls and strongly developed muscular bundles, vulval lips slightly protuberant, vulval flap absent, distal region of post-vulval uterine sac appearing as a weakly developed oogonia, anus and rectum indistinct, female posterior part (‘tail’) dorsally convex, conical, terminal region contracted into a bluntly pointed tip. The spicules are arcuate, 15.6 (14.3-16.3) μm along the chord, lamina smoothly curved to distal end, capitulum slightly concave, condylus well-developed with broadly rounded tip and slightly depressed at dorsal end, rostrum triangular with finely rounded tip, cucullus absent, and with seven caudal papillae present. The near full length 18S and 28S D2-D3 regions of rRNA genes sequences were characterised. The phylogenetic analyses revealed that the Fujian population of E. compsi grouped with the Zhejiang population of E. compsi, both being morphologically identical.

Detailed morphology of tentacular apparatus and central nervous system in Owenia borealis (Annelida, Oweniidae)

The Oweniidae are marine annelids with many unusual features of organ system, development, morphology, and ultrastructure. Together with magelonids, oweniids have been placed within the Palaeoannelida, a sister group to all remaining annelids. The study of this group may increase our understanding of the early evolution of annelids (including their radiation and diversification). In the current research, the morphology and ulta-anatomy of the head region of Owenia borealis is studied by scanning electron microscopy (SEM), 3D reconstructions, transmission electron microscopy (TEM), and whole-mount immunostaining with confocal laser scanning microscopy. According to SEM, the tentacle apparatus consists of 8–14 branched arms, which are covered by monociliary cells that form a ciliary groove extending along the oral side of the arm base. Each tentacle contains a coelomic cavity with a network of blood capillaries. Monociliary myoepithelial cells of the tentacle coelomic cavity form both the longitudinal and the transverse muscles. The structure of this myoepithelium is intermediate between a simple and pseudo-stratified myoepithelium. Overall, tentacles lack prominent zonality, i.e., co-localization of ciliary zones, neurite bundles, and muscles. This organization, which indicates a non-specialized tentacle crown in O. borealis and other oweniids with tentacles, may be ancestral for annelids. TEM, light, and confocal laser scanning microscopy revealed that the head region contains the anterior nerve center comprising of outer and inner (=circumoral) nerve rings. Both nerve rings are organized as concentrated nerve plexus, which contains perikarya and neurites extending between basal projections of epithelial cells (radial glia). The outer nerve ring gives rise to several thick neurite bundles, which branch and extend along aboral side of each tentacle. Accordingly to their immunoreactivity, both rings of the anterior nerve center could be homologized with the dorsal roots of circumesophageal connectives of the typical annelids. Accordingly to its ultrastructure, the outer nerve ring of O. borealis and so-called brain of other oweniids can not be regarded as a typical brain, i.e. the most anterior ganglion, because it lacks ganglionic structure.

Differential diagnosis of Dirofilaria immitis nematodes (Nematoda, Onchocercidae)

Heartworm disease is a widespread anthropozoonotic disease of carnivorous animals, as well as humans. It is caused by nematodes belonging to the suborder Filariata, family Onchocercidae, genus Dirofilaria. There are about 26 species of heartworms in nature, the most common and pathogenic species in dogs and cats in most countries is Dirofilaria immitis Leidy, 1856. Mature helminths parasitize in the right ventricle and pulmonary arteries, large veins of animals and cause heart and vascular disorders, and death. Therefore, the aim of the study was to investigate the features of morphological and metric structure of adult nematodes of D. immitis isolated from the heart of dogs. Morphological studies have shown that in males the most characteristic differential features are the presence of two unequal spicules, specifically positioned relative to each other, as well as well-defined preanal and less pronounced adanal and postanal papillae. In female heartworms, the characteristic morphological features are the shape and location of the vulva. There is a difference in the structure of the esophagus in males and females. In females, the anterior and posterior parts of the esophagus are well expressed, with enlargements, in males these divisions are not pronounced. To increase the efficiency of species identification of D. immitis nematodes, it is proposed to use metric parameters that characterize the overall body size, body and width of esophagus in different areas, length of esophagus, and the location of the nerve ring. In males, 11 indicators are also suggested that characterize the size of the spicules and the location of the cloaca. In females, seven additional parameters are pointed out that characterize the location of the vulva, anus and body width in these areas. The obtained data expand the already existing data on the peculiarities of the morphological structure of parasitic nematodes of the species D. immitis and their identification.

First Record of Dichelyne (Cucullanellus) tripapillatus (Nematoda: Cucullanidae) Parasitic in King Soldier Bream Argyrops spinifer (Pisces: Sparidae) in Arabian Gulf, off Iraq

A total of 42 specimens of Argyrops spinifer were caught from Iraqi territorial waters during the period from October 2019 till September 2020. The adult nematodes were isolated from the infected fishes. Morphological features of both males and females of nematodes matched with that of Dichelyne (Cucullanellus) tripapillatus (Gendre, 1927). This nematode is distinguished by the location of nerve ring in relation to the length of oesophagus, as well as the distribution of the ten caudal papillae of males. The record of this species and its subgenus represent its first one in the Arabian Gulf and Iraq.

A comparative analysis of the nervous system of cheilostome bryozoans

Background Bryozoans are sessile aquatic suspension feeders in mainly marine, but also freshwater habitats. Most species belong to the marine and calcified Cheilostomata. Since this taxon remains mostly unstudied regarding its neuroanatomy, the focus of this study is on the characterization and ground pattern reconstruction of the autozooidal nervous system based on six representatives. Results A common neuronal innervation pattern is present in the investigated species: a cerebral ganglion is located at the base of the lophophore, from where neurite bundles embrace the mouth opening to form a circumoral nerve ring. Four neurite bundles project from the cerebral ganglion to innervate peripheral areas, such as the body wall and parietal muscles via the tentacle sheath. Five neurite bundles comprise the main innervation of the visceral tract. Four neurite bundles innervate each tentacle via the circumoral nerve ring. Mediofrontal tentacle neurite bundles emerge directly from the nerve ring. Two laterofrontal- and one abfrontal tentacle neurite bundles emanate from radial neurite bundles, which originate from the cerebral ganglion and circumoral nerve ring in between two adjacent tentacles. The radial neurite bundles terminate in intertentacular pits and give rise to one abfrontal neurite bundle at the oral side and two abfrontal neurite bundles at the anal side. Similar patterns are described in ctenostome bryozoans. Conclusions The present results thus represent the gymnolaemate situation. Innervation of the tentacle sheath and visceral tract by fewer neurite bundles and tentacular innervation by four to six tentacle neurite bundles support cyclostomes as sister taxon to gymnolaemates. Phylactolaemates feature fewer distinct neurite bundles in visceral- and tentacle sheath innervation, which always split in nervous plexus, and their tentacles have six neurite bundles. Thus, this study supports phylactolaemates as sistergroup to myolaemates.

Molecular characterization of free-living nematodes from Kermadec Trench (Nematoda: Aegialoalaimidae, Xyalidae) with description of Aegialoalaimus tereticauda n. sp.

The Kermadec Trench is the world’s fifth deepest trench and extends from approximately 26 to 36°S near the northeastern tip of New Zealand’s North Island. Here, we describe a new species of Aegialoalaimus, a nematode genus with unusual buccal cavity and pharynx morphology, from a site at 9540 metres water depth in Kermadec Trench, and provide the first SSU and D2–D3 of LSU sequences for Aegialoalaimus, Manganonema, Metasphaerolaimus constrictus and Daptonema amphorum. Aegialoalaimus tereticauda n. sp. is characterised by body length 755–864 µm, cephalic sensilla papilliform (< 1 µm long), excretory pore located slightly anterior to posterior bulb in males and slightly anterior to nerve ring in females, arcuate spicules 18–22 µm long, gubernaculum present, precloacal supplements absent, and cylindrical tail 58–64 µm long with rounded tip. Relationships between Aegialoalaimus and Chromadorean orders could not be elucidated based on our SSU analysis; no link could be found with the Plectida, where the Aegialoalaimidae is currently placed, or with the Isolamiida or Cylindrolaimus (Areaolaimida), which share a similar and unusual buccal and pharynx morphology. Our SSU phylogenetic analysis confirms the placement of Manganonema within the Xyalidae, although relationships with other xyalid genera remain unclear. The Sphaerolaimidae formed a clade together with the Monhysteridae, which contradicts the current classification where the Sphaerolaimidae and Xyalidae are classified together into the superfamily Sphaerolaimoidea and the Monhysteridae into the Monhysteroidea. Although limited research has been conducted on the nematode diversity in Kermadec Trench to date, the available data show that half of all invertebrate species known from the trench are nematodes, which highlights the importance of conducting further taxonomic research on this group in hadal environments.

Supplementary characterisation of Bursaphelenchus leoni Baujard, 1980 (Tylenchina: Aphelenchoididae) found in Pinus massoniana from Zhejiang Province, China, with proposal of B. borealis Korentchenko, 1980 as a junior synonym

Summary Bursaphelenchus leoni is redescribed, using morphology, morphometrics and molecular data, based on a population isolated from dead Pinus massoniana in Zhejiang Province, China. It is characterised by a lateral field with three lines, a 12-15 μm long stylet with small basal swellings, excretory pore located one body diam. posterior to nerve ring, spicules mitten-shaped, dorsally and ventrally arcuate, with lamina smoothly tapering towards broadly rounded distal tip without hook-like process in the Chinese population, condylus broadly rounded with a small dorsally bent hook, rostrum triangle or conical with finely rounded tip. The bursal flap is long, spade-like with posterior margin truncate or irregular. A 2-3 μm long vulval flap is present. The female tail is long and conical (c′ = 5.3-6.9), with the terminus finely rounded, or occasionally pointed. The Zhejiang population of B. leoni is close to B. eidmanni and B. silvestris, which all belong to the leoni-group sensu Braasch et al. (2009). Comparison with the description of B. borealis led to the conclusion that B. leoni and B. borealis are conspecific, the latter being regarded as a junior synonym of the former.

A neurite-zippering mechanism, mediated by layer-specific expression of IgCAMs, regulates synaptic laminar specificity in the C. elegans nerve ring neuropil

A fundamental design principle of nervous systems is the grouping of neuronal contacts into layers within nerve bundles. The layered arrangement of neurites requires nanoscale precision in their placement within bundles, and this precision, which can not be exclusively explained by simple tip-directed outgrowth dynamics, underpins synaptic specificity and circuit architecture. Here we implement novel imaging methods and deep learning approaches to document the specific placement of single neurites during the assembly of the C. elegans nerve ring. We uncover a zippering mechanism that controls precise placement of neurites onto specific layer subdomains. Nanoscale precision in neurite placement is orchestrated via temporally-regulated expression of specific Ig adhesion molecules, such as SYG-1. Ig adhesion molecules act as instructive signals, defining sublaminar regions and guiding neurite zippering onto target neurons. Our study reveals novel developmental mechanisms that coordinate neurite placement and synaptic specificity within layered brain structures.

Aphelenchoides smolae n. sp. (Tylenchina: Aphelenchoididae) found in Lilium orientalis imported into China from The Netherlands

Summary Aphelenchoides smolae n. sp. isolated in Ningbo Port, China, from medium soil and tissues of Lilium orientalis bulbs imported from The Netherlands, is described. It is characterised by the female body length of 826 (672-1002) μm and male body length of 785 (683-844) μm, lateral field with four lines (three bands), stylet 13.0-14.9 μm long with small basal swellings, excretory pore situated slightly posterior to nerve ring, vulval flap absent, post-vulval uterine sac well developed and extending for ca 35.7-62.4% of vulva to anus distance, conical tail with terminus bearing a single mucron with many tiny nodular protuberances under SEM, males common, with spicules 25.7-29.8 μm long (median curved line), the condylus and rostrum rounded, well developed, the dorsal limb with a hook-like tip, and tail bearing three pairs (2 + 2 + 2) of caudal papillae and a sharply pointed mucron. The new species belongs to the Group 2 category of Aphelenchoides species sensu Shahina. Phylogenetic analysis based on 18S, 28S D2-D3 of rDNA and COI mtDNA further characterised the new species.

Structure and function of the nervous system in nectophores of the siphonophore Nanomia bijuga

SummaryAlthough Nanomia nectophores are specialized for locomotion, their cellular elements and complex nerve structures suggest they have multiple subsidiary functions.The main nerve complex is a nerve ring, an adjacent columnar-shaped matrix plus two associated nerve projections. An upper nerve tract appears to provide a sensory input while a lower nerve tract connects with the rest of the colony.The nerve cell cluster that gives rise to the lower nerve tract may relay information from the colony stem.The structure of the extensively innervated “flask cells” located around the bell margin suggests a secretory function. They are ideally placed to release chemical messengers or toxins into the jet of water that leaves the nectophore during each swim.The numerous nematocytes present on exposed nectophore ridges appear to have an entangling rather than a penetrating role.Movements of the velum, produced by contraction of the Claus’ muscle system during backwards swimming, can be elicited by electrical stimulation of the surface epithelium even when the major nerve tracts serving the nerve ring have been destroyed (confirming Mackie, 1964).Epithelial impulses generated by electrical stimulation elicit synaptic potentials in Claus’ muscle fibres. Their amplitude suggests a neural input in the vicinity of the Claus’ muscle system. The synaptic delay is <1.3 ms (Temperature 11.5 to 15° C).During backward swimming radial muscle fibres in the endoderm contract isometrically providing the Claus’ fibres with a firm foundation.Summary StatementNanomia colonies have specialized swimming bells capable of backwards swimming; thrust is redirected by an epithelial signal that leads to muscle contraction via a synaptic rather than an electrotonic event.