Antisera to the sequence Arg-Phe-amide visualize neuronal centralization in hydroid polyps

Summary Antisera to the sequence Arg-Phe-amide (RF-amide) have a high affinity to the nervous system of fixed hydroid polyps. Whole-mount incubations of several Hydra species with RFamide antisera visualize the three-dimensional structure of an ectodermal nervous system in the hypostome, tentacles, gastric region and peduncle. In the hypostome of Hydra attenuata a ganglion-like structure occurs, consisting of numerous sensory cells located in a region around the mouth opening and a dense plexus of processes which project mostly radially towards the bases of the tentacles. In Hydra oligactis an ectodermal nerve ring was observed lying at the border of hypostome and tentacle bases. This nerve ring consists of a few large ganglion cells with thick processes forming a circle around the hypostome. This is the first direct demonstration of a nerve ring in a hydroid polyp.Incubation of Hydractinia echinata gastrozooids with RFamide antisera visualizes an extremly dense plexus of neuronal processes in body and head regions. A ring of sensory cells around the mouth opening is the first group of neurons to show RFamide immunoreactivity during the development of a primary polyp. In gonozooids the oocytes and spermatophores are covered with strongly immunoreactive neurons.All examples of whole-mount incubations with RF-amide antisera clearly show that hydroid polyps have by no means a diffuse nerve net, as is often believed, and that neuronal centralization and plexus formation are common in these animals. The examples also show that treatment of intact fixed animals with RFamide antisera is a useful technique to study the anatomy or development of a principal portion of the hydroid nervous system.     

Early embryonic development of the head region of Gryllus assimilis Fabricius, 1775 (Orthoptera,Insecta)

We report our investigations on the embryonic development of Gryllus assimilis, with particular attention to the head. Significant findings revealed with scanning electron microscopy (SEM) images include: (1) the pre-antennal lobes represent the anterior-most segment that does not bear any appendages; (2) each of the lobes consists of central and marginal regions; (3) the central region thereof develops into the protocerebrum and the optic lobes, whereas the marginal region thereof becomes the anterior portion of the head capsule; (4) the initial position of the antennal segment is posterior to the mouth region; (5) appendage anlagen are transitorily present in the intercalary segment, and they later vanish together with the segment itself; (6) a bulged sternum appears to develop from the ventral surface of the mandibular, maxillary and labial segments. Embryonic features are then compared across the Insecta and further extended to the embryos of a spider (Araneae, Chelicerata). Striking similarities shared by the anterior-most region of the insect and spider embryos lead the authors to conclude that such comparison should be further undertaken to cover the entire Euarthropoda. This will help us to understand the embryology and evolution of the arthropod head.     

Histology of the neurosecretory system and neurohaemal organs of the spider, Argiope aurantia (Lucas)

The oval olfactory rosette of the carp Labeo rohita belongs to Burne's ('09) rosette column one or to Bateson's (1889) rosette type three. The total olfactory area of the fish is greater than its total retinal area; however, it has been classified with Teichmann's ('54) group of eye-nose fishes. Each olfactory chamber communicates with an anterior, ventral accessory sac; in spite of Burne's ('09) observation that accessory sacs are absent in carps. Movements of the jaw bones dilate and compress the accessory sac. Water is drawn in through the posterior opening (and not through the anterior as suggested by Liermann, '33, and Johnson and Brown, '62) and also expelled through it when the mouth opens and closes for normal respiratory function. Hence, the accessory sac does not draw water across the olfactory rosette through the anterior opening. At intervals, the fish opens its mouth full and wide and draws water into the chamber through the anterior opening as well.     

Scanning electron microscopy of Drosophila melanogaster embryogenesis: III. Formation of the head and caudal segments

The formation of both the anterior most and posterior most segments in higher dipteran embryos involves complex movements of primordia which can be best visualized with the scanning electron microscope. During head formation, the gnathocephalic segments partially involute through the stomodeum. The labial segment forms the floor of the mouth, and the fused maxillary and mandibular segments form the lateral sides of the mouth. The involuted clypeolabrum forms the roof of the mouth. Invaginations of cells for segmentally derived sense organs can be found prior to involution on all the gnathocephalic and thoracic segments as well as on the labrum. The antennal sense organ derives from the lateral surface of the procephalic lobe. Following involution of the mouth parts, the dorsal ridge, which arises just anterior to the first thoracic segment, is drawn over the dorsal procephalic lobe producing the deep dorsal sac. The optic lobes of the brain invaginate anterior to the dorsal ridge just prior to the covering over of the head. The formation of the anal segment is similarly complex. Two rudimentary segments are found posterior to the eighth abdominal segment. During shortening of the germ band, the posterior most segment is drawn around the posterior tip of the embryo to lie ventrally. Two large anal pads form lateral to the anus from this segment. The next segment, following dorsal closure, produces a pair of anal sense organs and a central tuft of setae. Finally, the eighth abdominal segment gives rise to the posterior spiracles. Following dorsal closure these three segments fuse to produce the terminal (anal) segment of the larva.     

Pentastomid Nymph From the Brain of a Squirrel Monkey (Saimiri sciureus). I. Morphology of the Nymph

A Pentastomid nymph of the genus Porocephalus was identified following its removal from the brain–meningeal interface of a squirrel monkey, Saimiri sciureus. It was characterized by two inner and two outer hooks adjacent to the mouth opening, the presence of accessory lobes (or spines) on the outer hooks, a vertical slit-like mouth opening surrounded by a U-shaped conformation of integument, and annulation of the body surface. Stigmata, representing the openings of integumental chloride cells, were present on the dorsum of the head and tail, on anterior aspects of annulae on the body, and on anterior and posterior edges of annulae located on the ventral surface of the tail. These openings were not present on integumental folds at the bases of the inner and outer hooks, on the dorsal aspect of the tail flap, or in the deep grooves separating annulae. Although it was not possible to determine the species, based on the number of annulae this specimen may represent P. stilesi.     

Microtopography of Nippostrongylus brasiliensis (Nematoda: Heligmosomatidae): Free-living larval stages

Microtopographic features of the various growth stages of the three free-living larval stages of the rat hookworm Nippostrongylus brasiliensis (Nematoda) were surveyed by scanning electron microscopy. These worms have a rounded anterior end and an elongated tail. Cuticular annulations were observed along the body, which also bore two ribbon-like lateral alae. Two rings of six lip-like lappets were observed around the triradiate oral opening in all larval stages. The cephalic space contained two lateral amphidial pits. The excretory pore in the third anterior part was observed in a ventral view of the larvae. No deirids were observed. The anus with a crescent-shape opening was located posteriorly. Phasmidial apertures, only observed in the third-stage larvae, opened on the lateral alae in the tail region. © 1993 Wiley-Liss, Inc.     

Molecular studies of hemichordate development: a key to understanding the evolution of bilateral animals and chordates

SUMMARY Using the Hawaiian acorn worm, Ptychodera flava, we began molecular studies on the development of hemichordates, a phylum previously unstudied at this level. Here we review results garnered from the examination of a few specific genes selected to help understand the evolution of vertebrate structures. These studies suggest new ideas about the evolution of developmental mechanisms in the deuterostomes. In a seminal observation, we noted an unexpected zone of expression of the Brachyury gene in the early anterior embryonic ectoderm where the mouth will form. Typically, the Brachyury gene is closely linked to development of the notochord and is expressed around the blastopore and in the posterior mesoderm in most animals. This first expression of Brachyury at the blastopore may represent a regulatory program associated with organizing the original animal head and gut opening, as suggested by the expression of Brachyury during hypostome formation in hydra. We believe that the anterior expression of Brachyury in deuterostomes represents the cooption of the program for organizing the original animal gut opening to form the deuterostome mouth. Recent data from the trochophore larva of a polychaete show that an anterior zone of expression of Brachyury is produced in this protostome by splitting of the Brachyury field during the formation of a gut with a mouth and anus by the lateral fusion of the sides of the blastopore. The ability to initiate independently a secondary regulatory program to organize the new mouth leading to an anterior field of Brachyury expression may be a signal event in the evolution of the deuterostomes. We also noted that the P. flava homolog of T‐brain/Eomes, a gene closely related by sequence and expression around the blastopore to Brachyury and associated with development of the vertebrate brain, also exhibits early posterior expression around the blastopore and a field of de novo anterior ectoderm expression during later embryogenesis. The tissue in the zone of de novo anterior ectoderm expression of Pf‐Tbrain produces the apical organ, a larval neural structure that has been touted as an evolutionary precursor of the chordate dorsal brain. The gene regulatory mechanisms responsible for initiating the anterior zone of de novo expression of T‐brain may represent a cooption to specify early neuroectoderm of the regulatory program evolved first to drive anterior Brachyury expression for deuterostome mouth formation. It will be interesting to examine the possibilities that an ability to initiate the de novo anterior expression of the program that includes T‐brain may be a key event in the evolution of the developmental mechanisms leading to the chordate dorsal nervous system.     

The mechanism of frill erection in the bearded dragon Amphibolurus barbatus with comments on the jacky lizard A. muricatus (Agamidae)

Amphibolurus barbatus has a threat display which includes the erection of the gular regions as a frill and may also include wide opening of the mouth to display a yellow mouth lining. Frill erection involves protraction, depression, and lateral expansion of the hyoid apparatus. Electrical stimulation of the hyoid muscles and dissection of the hyoid apparatus were used to examine specializations for producing frill erection. Specializations of the hyoid skeleton include the absence of a ceratobranchial II, presence of a synovial joint between the ceratohyal and body of the hyoid, and combined shortening of the entoglossal process and lengthening of the posterior arches. The only apparent specialization of the hyoid musculature is the anterior displacement of the origin of m. hyomandibularis. All of the hyoid muscles are involved in some way in frill erection and the actions of each muscle is described. The characteristic frill erection in the threat display of Amphibolurus barbatus is possible because of the 1:2 ratio of the anterior and posterior parts of the apparatus and the absence of the ceratobrnchial II.     

Visual fields of orb web and single line web spiders of the family Uloboridae (Arachnida,Araneida)

Summary In the family Uloboridae, web reduction is associated with changes in web monitoring posture and prosomal features. A spider must extend its first pair of legs directly forward to monitor the signal line of a reduced web. This posture is facilitated by shifts in prosomal musculature that cause reduced web uloborids to have a narrower anterior prosoma, a reduced or absent anterior eye row, and prominent posterior lateral eye tubercles. The eye tubercles and larger posterior eyes of these uloborids suggest that web reduction may also be accompanied by ocular changes that compensate for reduction of the anterior eyes by expanding the visual fields of the posterior eyes. A comparison of the visual fields of the eight-eyed, orb web species Octonoba octonaria and a four-eyed, reduced web Miagrammopes species was made to determine if this is true. Physical and optical measurements determined the visual angles of each species' eyes and the pattern of each species' visual surveillance. Despite loss of the anterior four eyes, the Miagrammopes species has a visual coverage similar to that of O. octonaria. This is due to (1) an increase in the visual field of each of the four remaining Miagrammopes eyes, accruing from an extension of the retina and an increase in the lens' rear radius of curvature, and (2) a ventral shift of each visual axis, associated with the development of an eye tubercle and an asymmetrical expansion of the retina. Miagrammopes monitor their simple webs from twigs or moss where they are vulnerable to predation. Therefore, maintenance of visual cover may enable them to detect predators in time to assume or maintain their characteristic, cryptic posture. It may also allow them to observe approaching prey and permit them to adjust web tension or prepare to jerk their webs when prey strikes.     

Gross morphology,histology, and ultrastructure of the alimentary system of Ricinulei (Arachnida) with emphasis on functional and phylogenetic implications

Ricinuleid functional mouthparts are the cucullus, the chelicerae, the pedipalps, and the labrum. These structures are movably jointed to the rest of the prosoma, most likely protruded upon hydrostatic hemolymph pressure and retracted by prosomal muscles. Seta‐like protrusions from the labrum and the pedipalpal coxae form a sieve‐like filter inside the preoral cavity and the mouth. Although the tip of the labrum can be elevated upon muscle constriction, ingestion of large, solid food particles is unlikely. The mouth has a crescent‐shaped cross section. The cuticle‐lined, also crescent‐shaped pharynx is equipped with a large dilator muscle but lacks antagonistic constrictor muscles. It represents a precerebral sucking pump. The triangular to Y‐shaped, cuticle‐lined esophagus is equipped with constrictor and dilator muscles. Its posterior part represents a postcerebral sucking pump. Four blind ending diverticula ramify from the anterior prosomal part of the entodermal midgut tube. Two of these diverticula remain inside the prosoma and form few short branches. The other two extend through the pedicel into the opisthosoma and ramify and coil there. A stercoral pocket protrudes ventrally out of the midgut tube. The most distal part of the midgut tube is modified into a contractile rectal gland. Its secretions may have defensive or physiological functions. A short anal atrium is formed by the cuticle‐lined ectodermal hindgut which opens at the end of the three‐segmented metasoma. The telescoping segments of the metasoma are protruded by hemolymph pressure and retracted by muscles. J. Morphol., 2011. © 2010 Wiley‐Liss, Inc.     

Variability of Acartia clausi in the Black Sea

There are two morphotypes of A. clausi in the Black Sea. The diversity in the spine ornamentation of the last prosomal and urosomal segments generally has been decreasing in both morphotypes during the period of this study (1976–1990). Seasonal data showed increased variability in April.     

Morphological and Molecular Characterization of Gracilacus wuae n. sp. (Nematoda: Criconematoidea) Associated with Cow Parsnip (Heracleum maximum) in Ontario,Canada

Gracilacus wuae n. sp. from soil associated with cow parsnip in Ontario, Canada is described and illustrated. Morphologically, females have a long stylet ranging from 80 to 93 µm long, the lip region not offset from the body contour, without lateral lips but with large and flat submedian lobes, the mouth opening slit-like elongated laterally and surrounded by lateral flaps, the excretory pore is anterior to the knobs of the stylet; males without stylet and the pharynx degenerated. The fourth-stage juveniles lack a stylet, the pharynx degenerated, and can be differentiated into preadult females and males based on the position of the genital primordia. The third-stage juveniles are similar to females but smaller. Phylogenetic studies using the rDNA small subunit 18S, large subunit 28S D2/D3, and internal transcribed spacer (ITS) sequences collectively provide evidence of a grouping with other Gracilacus and some species of Paratylenchus with stylet length of females longer than 41 µm deposited in GenBank.     

Segmental organisation of the head in the embryo of Drosophila melanogaster

Summary Embryos of Drosophila melanogaster were irradiated in the presumptive head region with a UV-laser microbeam of 20 m diameter at two developmental stages, the cellular blastoderm and the extended germ band. The ensuing defects were scored in the cuticle pattern of the head of the first-instar larva, which is described in detail in this paper. The defects caused by irradiating germ band embryos when morphologically recognisable lobes appear in the head region were used to establish the segmental origin of various head structures. This information enabled us to translate the spatial distribution of blastoderm defects into a fate map of segment anlagen. The gnathal segments derive from a region of the blastoderm between 60% and 70% egg length (EL) dorsally and 60% and 80% ventrally. The area anterior to the mandibular anlage and posterior to the stomodaeum is occupied by the small anlagen of the intercalary and antennal segments ventrally and dorsally, respectively. The labrum, which originates from a paired anlage dorsally at 90% EL, is separated from the remaining head segments by an area for which we did not observe cuticle defects following blastoderm irradiation, presumably because those cells give rise to the brain. The dorsal and lateral parts of the cephalo-pharyngeal skeleton appear to be the only cuticle derivatives of the non-segmental acron. These structures derive from a dorso-lateral area just behind the putative brain anlage and may overlap the latter. In addition to the segment anlagen, the regions of the presumptive dorsal pouch, anterior lobe and post-oral epithelium, whose morphogenetic movements during head involution result in the characteristic acephalic appearance of the larva, have been projected onto the blastoderm fate map. The results suggest that initially the head of the Drosophila embryo does not differ substantially from the generalised insect head as judged by comparison of fate map and segmental organisation.     

Morphological reinvestigation and phylogenetic relationship of Acanthobdella peledina (Annelida,Clitellata)

Summary In recently collected specimens of Acanthobdella peledina the nervous system, the genital organs and the coelomic organisation were reinvestigated after complete serial sections. These anatomical results are schematically represented. In addition, the integument, the chaetae and the peripheral muscle layer were investigated by electron microscopy. In general, the results confirm Livanow's classic monograph (1906), with the exception of a few details. The body apparently possesses neither a prostomium nor an achaetous buccal region (peristomium). The number of 29 true segments is concluded from the number of segmental ganglia. The five anteriormost segments, each with four pairs of hookshaped chaetae arranged around the mouth opening, are considered to be functionally equivalent to an anterior sucker. The ultrastructure of the integument and the chaetae generally conforms to the typical annelidan pattern. The muscle cells are of the typical hirudinean type. The outer male genital pore is positioned in segment 10; the female organs open in segment 11 directly behind the septum between segments 10 and 11. The main emphasis is laid on the evaluation of the position of the taxon within the Clitellata, including a discussion of the Branchiobdellida, and the cladograms presented show the Acanthobdellida to be the sister group of the Euhirudinea. Characters shared by the Branchiobdellida and Hirudinea (including A. peledina) are considered to be convergently evolved.     

The fowl tick, <Emphasis Type="Italic">Argas (Persicargas) persicus</Emphasis> (Ixodoidea: Argasidae): Description of the egg and redescription of the larva by Scanning Electron Microscopy

This scanning electron microscopy study revealed that the egg of Argas persicus was covered with chorion which appeared as a wrinkled layer containing regions of three textures. The first had elevated parts of slightly rough surface. The second had irregular smooth elevations; each carried numerous parallel horizontal foldings with vertical ridges. The last region had rough surface with irregularly shaped projections. Following the removal of the chorion, shell was observed to have one polar micropyle and numerous slit like openings. Length (L), width (W) and L/W ratio of the egg were measured. Investigation of larvae revealed extensively folded integument of idiosoma and spherical or elongated tubercles on dorsal plate. Mouth enclosed between ventral hypostome and two dorsal chelicerae. Hypostome carried four longitudinal rows of conical denticles. Each chelicera was made up of two segments; the basal one appeared as a pocket for the distal one. Haller’s organ consisted of an anterior pit containing seven sensilla and a posterior capsule with four apertures. Distribution of chemo- and mechano-sensilla on the body was examined. Measurements of whole body, idiosoma, dorsal plate, capitulum, hypostome, palp and different types of sensilla both on the body and Haller’s organ are also presented.     

Fine structure and function of the prosomal glands of the two-spotted spider mite,Tetranychus urticae (Acari,Tetranychidae)

Summary The prosomal glands of Tetranychus urticae (Acari, Tetranychidae) were examined light and electron microscopically. Five paired and one unpaired gland are found both in females and males. The silk spinning apparatus consists of paired silk glands which extend laterally on both sides of the esophagus into the pedipalps. There, they enter the terminal silk gland bag which opens into a silk bristle at the apex of the pedipalps. The salivary secretions are formed in three paired glands which have an interconnecting duct, the podocephalic canal. The dorsal podocephalic glands may produce a serous secretion, the anterior podocephalic glands a mucous secretion, and the coxal organ may add a liquid, ion-rich secretion. These secretions pass the podocephalic canal and reach the mouth at the apex of the gnathosome. The function of the paired tracheal organs and the unpaired tracheal gland is still unclear. The tracheal gland may produce a secretion which facilitates the movement of the fused chelicerae and the stylets.This study was financed by a grant from the Deutsche Forschungsgemeinschaft (DFG Se 162/12)     

Prey capture behavior and kinematics of the Atlantic cownose ray, Rhinoptera bonasus

The structurally reinforced jaws of the cownose ray, Rhinoptera bonasus testify to this species' durophagous diet of mollusks, but seem ill-suited to the behaviors necessary for excavating such prey. This study explores this discordance by investigating the prey excavation and capture kinematics of R. bonasus. Based on the basal suction feeding mechanism in this group of fishes, we hypothesized a hydraulic method of excavation. As expected, prey capture kinematics of R. bonasus show marked differences relative to other elasmobranchs, relating to prey excavation and use of the cephalic lobes (modified anterior pectoral fin extensions unique to derived myliobatiform rays). Prey are excavated by repeated opening and closing of the jaws to fluidize surrounding sand. The food item is then enclosed laterally by the depressed cephalic lobes, which transport it toward the mouth for ingestion by inertial suction. Unlike in most sharks, upper jaw protrusion and mandibular depression are simultaneous. During food capture, the ray's spiracle, mouth, and gill slit movements are timed such that water enters only the mouth (e.g., the spiracle closes prior to prey capture and reopens immediately following). Indigestible parts are then hydraulically winnowed from edible prey portions, by mouth movements similar to those used in excavation, and ejected through the mouth. The unique sensory/manipulatory capabilities of the cephalic lobes, as well as the cownose ray's hydraulic excavation/winnowing behaviors and suction feeding, make this species an effective benthic predator, despite its epibenthic lifestyle.     

The morphology of the upper lip of Cypridoidea ostracods: taxonomic and phylogenetic significance

This paper represents the first study of the morphology of the upper lip (labrum) and hypostome of ostracods using scanning electron microscopy (S.E.M.). There is considerable variation in the upper lip morphology of the 23 species of Cypridoidea (Podocopina) ostracods used in this study. The detail of the upper lip morphology of each species is very distinctive, so that species determination can be made on this feature alone, but it is not useful in diagnosing genera or subfamilies. The hypostome is not readily studied due to the large amounts of dense pseudochaetae (small, setae-like projections) protruding from it and hence is considered not to be a useful taxonomic feature. Several features of the upper lip and mouth region are documented for the first time. Comparisons of the general morphology of the upper lips of Recent ostracods with the upper lip of the fossil ostracod Pattersoncypris micropapillosa Bate, 1972, indicate that there has been very conservative evolution in these features since the Cretaceous.     

A Larval Sea Spider (Arthropoda: Pycnogonida) from the Upper Cambrian 'orsten' of Sweden, and the Phylogenetic Position of Pycnogonids

Among a set of small, secondarily phosphatised larval arthropods from the Upper Cambrian 'Orsten' of Sweden, described by Müller and Walossek in 1986, one form bears a remarkable resemblance to the hatching protonymph larva of extant Pantopoda. This 'larva D' shares with protonymphs their gross body form, the anteroventral mouth on a slightly off-set forehead region, the cheliceral morphology, two homeomorphic pairs of post-cheliceral limbs, and further detailed similarities. It is described herein as Cambropycnogon klausmuelleri gen. et sp. nov. and is proposed as the oldest unequivocal record of both Pycnogonida and Chelicerata. Plesiomorphic features such as a pair of rudimentary pre-cheliceral limbs and the gnathobasic basipods of the two post-cheliceral limbs distinguish it from all known larvae of extant Pantopoda and lead us to propose a phylogeny of the Pycnogonida of the form ( Cambropycnogon klausmuelleri + ( Palaeoisopus + ( Palaeopantopus + Pantopoda))). The fossil may help to resolve the long debate about the relationships of Pycnogonida to other Arthropoda and supports a (Pycnogonida + Euchelicerata) relationship within the Chelicerata. The pre-cheliceral limbs in this fossil support traditional morphological studies in which the chelicera represent the second (a2) head appendage, corresponding to the crustacean 'second antennae', and contradict recent data based on homeobox genes implying that the chelicerae are the first (a1) head appendages homologous with crustacean first antennae.